Cytochromes p450

A novel step towards the heterologous biosynthesis of paclitaxel: Characterization of T1βOH taxane hydroxylase

In the quest for innovative cancer therapeutics, paclitaxel remains a cornerstone in clinical oncology. However, its complex biosynthetic pathway, particularly the intricate oxygenation steps, has remained a puzzle in the decades following the characterization of the last taxane hydroxylase. The high divergence and promiscuity of enzymes involved have posed significant challenges. In this study, we adopted an innovative approach, combining in silico methods and functional gene analysis, to shed light on this elusive pathway. Our molecular docking investigations using a library of potential ligands uncovered TB574 as a potential missing enzyme in the paclitaxel biosynthetic pathway, demonstrating auspicious interactions. Complementary in vivo assays utilizing engineered S. cerevisiae strains as novel microbial cell factory consortia not only validated TB574's critical role in forging the elusive paclitaxel intermediate, T5αAc-1β,10β-diol, but also achieved the biosynthesis of paclitaxel precursors at an unprecedented yield including T5αAc-1β,10β-diol with approximately 40 mg/L. This achievement is highly promising, offering a new direction for further exploration of a novel metabolic engineering approaches using microbial consortia. In conclusion, our study not only furthers study the roles of previously uncharacterized enzymes in paclitaxel biosynthesis but also forges a path for pioneering advancements in the complete understanding of paclitaxel biosynthesis and its heterologous production. The characterization of T1βOH underscores a significant leap forward for future advancements in paclitaxel production using heterologous systems to improve cancer treatment and pharmaceutical production, thereby holding immense promise for enhancing the efficacy of cancer therapies and the efficiency of pharmaceutical manufacturing.

Genetic control of abiotic stress-related specialized metabolites in sunflower

BACKGROUND

Abiotic stresses in plants include all the environmental conditions that significantly reduce yields, like drought and heat. One of the most significant effects they exert at the cellular level is the accumulation of reactive oxygen species, which cause extensive damage. Plants possess two mechanisms to counter these molecules, i.e. detoxifying enzymes and non-enzymatic antioxidants, which include many classes of specialized metabolites. Sunflower, the fourth global oilseed, is considered moderately drought resistant. Abiotic stress tolerance in this crop has been studied using many approaches, but the control of specialized metabolites in this context remains poorly understood. Here, we performed the first genome-wide association study using abiotic stress-related specialized metabolites as molecular phenotypes in sunflower. After analyzing leaf specialized metabolites of 450 hybrids using liquid chromatography-mass spectrometry, we selected a subset of these compounds based on their association with previously known abiotic stress-related quantitative trait loci. Eventually, we characterized these molecules and their associated genes.

RESULTS

We putatively annotated 30 compounds which co-localized with abiotic stress-related quantitative trait loci and which were associated to seven most likely candidate genes. A large proportion of these compounds were potential antioxidants, which was in agreement with the role of specialized metabolites in abiotic stresses. The seven associated most likely candidate genes, instead, mainly belonged to cytochromes P450 and glycosyltransferases, two large superfamilies which catalyze greatly diverse reactions and create a wide variety of chemical modifications. This was consistent with the high plasticity of specialized metabolism in plants.

CONCLUSIONS

This is the first characterization of the genetic control of abiotic stress-related specialized metabolites in sunflower. By providing hints concerning the importance of antioxidant molecules in this biological context, and by highlighting some of the potential molecular mechanisms underlying their biosynthesis, it could pave the way for novel applications in breeding. Although further analyses will be required to better understand this topic, studying how antioxidants contribute to the tolerance to abiotic stresses in sunflower appears as a promising area of research.

Genome-wide identification and expression analyses of CYP450 genes in sweet potato (Ipomoea batatas L.)

BACKGROUND

Cytochrome P450 monooxygenases (CYP450s) play a crucial role in various biochemical reactions involved in the synthesis of antioxidants, pigments, structural polymers, and defense-related compounds in plants. As sweet potato (Ipomoea batatas L.) holds significant economic importance, a comprehensive analysis of CYP450 genes in this plant species can offer valuable insights into the evolutionary relationships and functional characteristics of these genes.

RESULTS

In this study, we successfully identified and categorized 95 CYP450 genes from the sweet potato genome into 5 families and 31 subfamilies. The predicted subcellular localization results indicate that CYP450s are distributed in the cell membrane system. The promoter region of the IbCYP450 genes contains various cis-acting elements related to plant hormones and stress responses. In addition, ten conserved motifs (Motif1-Motif10) have been identified in the IbCYP450 family proteins, with 5 genes lacking introns and only one exon. We observed extensive duplication events within the CYP450 gene family, which may account for its expansion. The gene duplication analysis results showed the presence of 15 pairs of genes with tandem repeats. Interaction network analysis reveals that IbCYP450 families can interact with multiple target genes and there are protein-protein interactions within the family. Transcription factor interaction analysis suggests that IbCYP450 families interact with multiple transcription factors. Furthermore, gene expression analysis revealed tissue-specific expression patterns of CYP450 genes in sweet potatoes, as well as their response to abiotic stress and plant hormones. Notably, quantitative real-time polymerase chain reaction (qRT‒PCR) analysis indicated the involvement of CYP450 genes in the defense response against nonbiological stresses in sweet potatoes.

CONCLUSIONS

These findings provide a foundation for further investigations aiming to elucidate the biological functions of CYP450 genes in sweet potatoes.

Antioxidants of Non-Enzymatic Nature: Their Function in Higher Plant Cells and the Ways of Boosting Their Biosynthesis

Plants are exposed to a variety of abiotic and biotic stresses leading to increased formation of reactive oxygen species (ROS) in plant cells. ROS are capable of oxidizing proteins, pigments, lipids, nucleic acids, and other cell molecules, disrupting their functional activity. During the process of evolution, numerous antioxidant systems were formed in plants, including antioxidant enzymes and low molecular weight non-enzymatic antioxidants. Antioxidant systems perform neutralization of ROS and therefore prevent oxidative damage of cell components. In the present review, we focus on the biosynthesis of non-enzymatic antioxidants in higher plants cells such as ascorbic acid (vitamin C), glutathione, flavonoids, isoprenoids, carotenoids, tocopherol (vitamin E), ubiquinone, and plastoquinone. Their functioning and their reactivity with respect to individual ROS will be described. This review is also devoted to the modern genetic engineering methods, which are widely used to change the quantitative and qualitative content of the non-enzymatic antioxidants in cultivated plants. These methods allow various plant lines with given properties to be obtained in a rather short time. The most successful approaches for plant transgenesis and plant genome editing for the enhancement of biosynthesis and the content of these antioxidants are discussed.

Large haploblocks underlie rapid adaptation in the invasive weed Ambrosia artemisiifolia

Adaptation is the central feature and leading explanation for the evolutionary diversification of life. Adaptation is also notoriously difficult to study in nature, owing to its complexity and logistically prohibitive timescale. Here, we leverage extensive contemporary and historical collections of Ambrosia artemisiifolia-an aggressively invasive weed and primary cause of pollen-induced hayfever-to track the phenotypic and genetic causes of recent local adaptation across its native and invasive ranges in North America and Europe, respectively. Large haploblocks-indicative of chromosomal inversions-contain a disproportionate share (26%) of genomic regions conferring parallel adaptation to local climates between ranges, are associated with rapidly adapting traits, and exhibit dramatic frequency shifts over space and time. These results highlight the importance of large-effect standing variants in rapid adaptation, which have been critical to A. artemisiifolia's global spread across vast climatic gradients.

Illuminating the biosynthesis pathway genes involved in bioactive specific monoterpene glycosides in Paeonia veitchii Lynch by a combination of sequencing platforms

BACKGROUND

Paeonia veitchii Lynch, a well-known herb from the Qinghai-Tibet Plateau south of the Himalayas, can synthesize specific monoterpene glycosides (PMGs) with multiple pharmacological activities, and its rhizome has become an indispensable ingredient in many clinical drugs. However, little is known about the molecular background of P. veitchii, especially the genes involved in the biosynthetic pathway of PMGs.

RESULTS

A corrective full-length transcriptome with 30,827 unigenes was generated by combining next-generation sequencing (NGS) and single-molecule real-time sequencing (SMRT) of six tissues (leaf, stem, petal, ovary, phloem and xylem). The enzymes terpene synthase (TPS), cytochrome P450 (CYP), UDP-glycosyltransferase (UGT), and BAHD acyltransferase, which participate in the biosynthesis of PMGs, were systematically characterized, and their functions related to PMG biosynthesis were analysed. With further insight into TPSs, CYPs, UGTs and BAHDs involved in PMG biosynthesis, the weighted gene coexpression network analysis (WGCNA) method was used to identify the relationships between these genes and PMGs. Finally, 8 TPSs, 22 CYPs, 7 UGTs, and 2 BAHD genes were obtained, and these putative genes were very likely to be involved in the biosynthesis of PMGs. In addition, the expression patterns of the putative genes and the accumulation of PMGs in tissues suggested that all tissues are capable of biosynthesizing PMGs and that aerial plant parts could also be used to extract PMGs.

CONCLUSION

We generated a large-scale transcriptome database across the major tissues in P. veitchii, providing valuable support for further research investigating P. veitchii and understanding the genetic information of plants from the Qinghai-Tibet Plateau. TPSs, CYPs, UGTs and BAHDs further contribute to a better understanding of the biology and complexity of PMGs in P. veitchii. Our study will help reveal the mechanisms underlying the biosynthesis pathway of these specific monoterpene glycosides and aid in the comprehensive utilization of this multifunctional plant.

Metabolome and transcriptome associated analysis of sesquiterpenoid metabolism in Nardostachys jatamansi

BACKGROUND

Nardostachys jatamansi, an extremely endangered valuable plant of the alpine Himalayas, can synthesize specific sesquiterpenoids with multiple effective therapies and is widely exploited for the preparation of drugs, cosmetics and even religious functions (e.g., well-known spikenard). However, how accumulation trend of the sesquiterpenoids in tissues and the molecular mechanisms underlying the production of the active ingredients are not well understood.

METHODS

The single-molecule real-time (SMRT) and RNA-seq transcriptome sequencing were combined to analyse the roots, rhizomes, leaves, flowers and anthocaulus of N. jatamansi. The phytochemical analysis was performed by gas chromatography‒mass spectrometry (GC‒MS) and ultrahigh-performance liquid chromatography (UPLC).

RESULTS

A high-quality full-length reference transcriptome with 26,503 unigenes was generated for the first time. For volatile components, a total of sixty-five compounds were successfully identified, including fifty sesquiterpenoids. Their accumulation levels in five tissues were significantly varied, and most of the sesquiterpenoids were mainly enriched in roots and rhizomes. In addition, five aromatic compounds were only detected in flowers, which may help the plant attract insects for pollination. For nonvolatile ingredients, nardosinone-type sesquiterpenoids (nardosinone, kanshone C, and isonardosinone) were detected almost exclusively in roots and rhizomes. The candidate genes associated with sesquiterpenoid biosynthesis were identified by transcriptome analysis. Consistently, it was found that most biosynthesis genes were abundantly expressed in the roots and rhizomes according to the functional enrichment and expression patterns results. There was a positive correlation between the expression profile of genes related to the biosynthesis and the accumulation level of sesquiterpenoids in tissues. Gene family function analysis identified 28 NjTPSs and 43 NjCYPs that may be involved in the biosynthesis of the corresponding sesquiterpenoids. Furthermore, gene family functional analysis and gene coexpression network analysis revealed 28 NjTPSs and 43 NjCYPs associated with nardosinone-type sesquiterpenoid biosynthesis.

CONCLUSION

Our research results reveal the framework of sesquiterpenoids accumulation and biosynthesis in plant tissues and provide valuable support for further studies to elucidate the molecular mechanisms of sesquiterpenoid regulation and accumulation in N. jatamansi and will also contribute to the comprehensive utilization of this alpine plant.

First purified recombinant CYP75B including transmembrane helix with unexpected high substrate specificity to (2R)-naringenin

Anthochlor pigments (chalcones and aurones) play an important role in yellow flower colourization, the formation of UV-honey guides and show numerous health benefits. The B-ring hydroxylation of chalcones is performed by membrane bound cytochrome P450 enzymes. It was assumed that usual flavonoid 3′-hydroxlases (F3′Hs) are responsible for the 3,4- dihydroxy pattern of chalcones, however, we previously showed that a specialized F3′H, namely chalcone 3-hydroxylase (CH3H), is necessary for the hydroxylation of chalcones. In this study, a sequence encoding membrane bound CH3H from Dahlia variabilis was recombinantly expressed in yeast and a purification procedure was developed. The optimized purification procedure led to an overall recovery of 30% recombinant DvCH3H with a purity of more than 84%. The enzyme was biochemically characterized with regard to its kinetic parameters on various substrates, including racemic naringenin, as well as its enantiomers (2S)-, and (2R)-naringenin, apigenin and kaempferol. We report for the first time the characterization of a purified Cytochrome P450 enzyme from the flavonoid biosynthesis pathway, including the transmembrane helix. Further, we show for the first time that recombinant DvCH3H displays a higher affinity for (2R)-naringenin than for (2S)-naringenin, although (2R)-flavanones are not naturally formed by chalcone isomerase.

Fine mapping of a novel QTL CsFSG1 for fruit skin gloss in cucumber (Cucumis sativus L.)

Cucumber (Cucumis sativus L.) is an important vegetable crop that is popular with many people. Peel gloss is a highly valued external quality trait that affects the market value of cucumbers, and it directly influences the purchasing psychology of consumers. Nonetheless, the candidate genes and underlying genetic mechanism for this important cucumber trait are not well understood. In this study, we successfully mapped a fruit skin gloss QTL interval to chromosome 3 (26.04-26.14 Mb) using BSA and GWAS methods. Among the eleven candidate genes in the interval, the cytochrome P450 family gene CsCYP86B1 was identified as the candidate for control of fruit skin gloss in cucumber. The expression of CsCYP86B1 in 0-day fruit skin was significantly lower in the low-gloss isogenic line NIL-1334 than in the high-gloss isogenic line NIL-1325. Our findings provide new insights for improving fruit skin gloss in cucumber breeding.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-022-01291-y.

Molecular characterization of three CYP450 genes reveals their role in withanolides formation and defense in Withania somnifera, the Indian Ginseng

The medicinal properties of Ashwagandha (Withania somnifera) are attributed to triterpenoid steroidal lactones, withanolides, which are proposed to be derived from phytosterol pathway, through the action of cytochrome P450 (CYP450) enzymes. Here, we report the characterization of three transcriptome-mined CYP450 genes (WsCYP749B1, WsCYP76 and WsCYP71B10), which exhibited induced expression in response to methyl jasmonate treatment indicating their role in secondary metabolism. All three WsCYP450s had the highest expression in leaf compared to other tissues. In planta characterization of WsCYP450s through virus induced gene silencing (VIGS) and transient overexpression approaches and subsequent metabolite analysis indicated differential modulation in the accumulation of certain withanolides in W. somnifera leaves. While WsCYP749B1-vigs significantly enhanced withaferin A (~ 450%) and reduced withanolide A (~ 50%), its overexpression drastically led to enhanced withanolide A (> 250%) and withanolide B (> 200%) levels and reduced 12-deoxywithastramonolide (~ 60%). Whereas WsCYP76-vigs led to reduced withanolide A (~ 60%) and its overexpression increased withanolide A (~ 150%) and reduced 12-deoxywithastramonolide (~ 60%). Silencing and overexpression of WsCYP71B10 resulted in significant reduction of withanolide B (~ 50%) and withanolide A (~ 60%), respectively. Further, while VIGS of WsCYP450s negatively affected the expression of pathogenesis-related (PR) genes and compromised tolerance to bacteria P. syringae DC3000, their overexpression in W. somnifera and transgenic tobacco led to improved tolerance to the bacteria. Overall, these results showed that the identified WsCYP450s have a role in one or several steps of withanolides biosynthetic pathway and are involved in conferring tolerance to biotic stress.

Overexpression of the Panax ginseng CYP703 Alters Cutin Composition of Reproductive Tissues in Arabidopsis

Cytochrome P450 (CYP) catalyzes a wide variety of monooxygenation reactions in plant primary and secondary metabolisms. Land plants contain CYP703, belonging to the CYP71 clan, which catalyzes the biochemical pathway of fatty acid hydroxylation, especially in male reproductive tissues. Korean/Asian ginseng (Panax ginseng Meyer) has been regarded as one of important medicinal plant for a long time, however the molecular mechanism is less known on its development. In this study, we identified and characterized a CYP703A gene in P. ginseng (PgCYP703A4), regarding reproductive development. PgCYP703A4 shared a high-sequence identity (81–83%) with predicted amino acid as CYP703 in Dancus carota, Pistacia vera, and Camellia sinensis as well as 76% of amino acid sequence identity with reported CYP703 in Arabidopsis thaliana and 75% with Oryza sativa. Amino acid alignment and phylogenetic comparison of P. ginseng with higher plants and known A. thaliana members clearly distinguish the CYP703 members, each containing the AATDTS oxygen binding motif and PERH as a clade signature. The expression of PgCYP704B1 was only detected in P. ginseng flower buds, particularly in meiotic cells and the tapetum layer of developing anther, indicating the conserved role on male reproduction with At- and Os- CYP703. To acquire the clue of function, we transformed the PgCYP703A4 in A. thaliana. Independent overexpressing lines (PgCYP703A4ox) increased silique size and seed number, and altered the contents of fatty acids composition of cutin monomer in the siliques. Our results indicate that PgCYP703A4 is involved in fatty acid hydroxylation which affects cutin production and fruit size.

Comparative Transcriptomics of Non-Embryogenic and Embryogenic Callus in Semi-Recalcitrant and Non-Recalcitrant Upland Cotton Lines

Somatic embryogenesis-mediated plant regeneration is essential for the genetic manipulation of agronomically important traits in upland cotton. Genotype specific recalcitrance to regeneration is a primary challenge in deploying genome editing and incorporating useful transgenes into elite cotton germplasm. In this study, transcriptomes of a semi-recalcitrant cotton (Gossypium hirsutum L.) genotype ‘Coker312’ were analyzed at two critical stages of somatic embryogenesis that include non-embryogenic callus (NEC) and embryogenic callus (EC) cells, and the results were compared to a non-recalcitrant genotype ‘Jin668’. We discovered 305 differentially expressed genes in Coker312, whereas, in Jin668, about 6-fold more genes (2155) were differentially expressed. A total of 154 differentially expressed genes were common between the two genotypes. Gene enrichment analysis of the upregulated genes identified functional categories, such as lipid transport, embryo development, regulation of transcription, sugar transport, and vitamin biosynthesis, among others. In Coker312 EC cells, five major transcription factors were highly upregulated: LEAFY COTYLEDON 1 (LEC1), WUS-related homeobox 5 (WOX5), ABSCISIC ACID INSENSITIVE3 (ABI3), FUSCA3 (FUS3), and WRKY2. In Jin668, LEC1, BABY BOOM (BBM), FUS3, and AGAMOUS-LIKE15 (AGL15) were highly expressed in EC cells. We also found that gene expression of these embryogenesis genes was typically higher in Jin668 when compared to Coker312. We conclude that significant differences in the expression of the above genes between Coker312 and Jin668 may be a critical factor affecting the regenerative ability of these genotypes.

The cytochrome P450 (CYP) superfamily in cnidarians

The cytochrome P450 (CYP) superfamily is a diverse and important enzyme family, playing a central role in chemical defense and in synthesis and metabolism of major biological signaling molecules. The CYPomes of four cnidarian genomes (Hydra vulgaris, Acropora digitifera, Aurelia aurita, Nematostella vectensis) were annotated; phylogenetic analyses determined the evolutionary relationships amongst the sequences and with existing metazoan CYPs. 155 functional CYPs were identified and 90 fragments. Genes were from 24 new CYP families and several new subfamilies; genes were in 9 of the 12 established metazoan CYP clans. All species had large expansions of clan 2 diversity, with H. vulgaris having reduced diversity for both clan 3 and mitochondrial clan. We identified potential candidates for xenobiotic metabolism and steroidogenesis. That each genome contained multiple, novel CYP families may reflect the large evolutionary distance within the cnidarians, unique physiology in the cnidarian classes, and/or different ecology of the individual species.

Diversity and evolution of cytochrome P450s of Jacobaea vulgaris and Jacobaea aquatica

BACKGROUND

Collectively, plants produce a huge variety of secondary metabolites (SMs) which are involved in the adaptation of plants to biotic and abiotic stresses. The most characteristic feature of SMs is their striking inter- and intraspecific chemical diversity. Cytochrome P450 monooxygenases (CYPs) often play an important role in the biosynthesis of SMs and thus in the evolution of chemical diversity. Here we studied the diversity and evolution of CYPs of two Jacobaea species which contain a characteristic group of SMs namely the pyrrolizidine alkaloids (PAs).

RESULTS

We retrieved CYPs from RNA-seq data of J. vulgaris and J. aquatica, resulting in 221 and 157 full-length CYP genes, respectively. The analyses of conserved motifs confirmed that Jacobaea CYP proteins share conserved motifs including the heme-binding signature, the PERF motif, the K-helix and the I-helix. KEGG annotation revealed that the CYPs assigned as being SM metabolic pathway genes were all from the CYP71 clan but no CYPs were assigned as being involved in alkaloid pathways. Phylogenetic analyses of full-length CYPs were conducted for the six largest CYP families of Jacobaea (CYP71, CYP76, CYP706, CYP82, CYP93 and CYP72) and were compared with CYPs of two other members of the Asteraceae, Helianthus annuus and Lactuca sativa, and with Arabidopsis thaliana. The phylogenetic trees showed strong lineage specific diversification of CYPs, implying that the evolution of CYPs has been very fast even within the Asteraceae family. Only in the closely related species J. vulgaris and J. aquatica, CYPs were found often in pairs, confirming a close relationship in the evolutionary history.

CONCLUSIONS

This study discovered 378 full-length CYPs in Jacobaea species, which can be used for future exploration of their functions, including possible involvement in PA biosynthesis and PA diversity.

Overexpression of a novel cytochrome P450 monooxygenase gene, CYP704B1, from Panax ginseng increase biomass of reproductive tissues in transgenic Arabidopsis

Cytochrome P450 monooxygenase 704B (CYP704B), a member of the CYP86 clan, was found to be needed in Arabidopsis and rice to biosynthesize precursors of sporopollenin through oxidizing fatty acids. In the present study, we cloned and characterized a CYP704B gene in Panax ginseng, named PgCYP704B1. It shared high sequence identity (98-99%) with CYP704 of Arabidopsis, Theobroma cacao, and Morus notabilis. The phylogenetic comparison of ginseng and higher plants between the members of CYP86 clan revealed that ginseng CYP704 was categorized as a group of CYP704B with dicot plants. The expression of PgCYP704B1 is low in the stem, leaf, and fruit, and high in flower buds, particularly detected in the young gametic cell and tapetum layer of the developing anther. Arabidopsis plants overexpressing PgCYP704B1 improved plant biomass such as plant height, siliques and seed number and size. A cytological observation by transverse and longitudinal semi-thin sections of the siliques cuticles revealed that the cell length increased. Furthermore a chemical analysis showed that PgCYP704B1ox lines increased their cutin monomers contents in the siliques. Our results suggest that PgCYP704B1 has a conserved role during male reproduction for fatty acid biosynthesis and its overexpression increases cutin monomers in siliques that eventually could be used for seed production.

A Novel Hydroxylation Step in the Taxane Biosynthetic Pathway: A New Approach to Paclitaxel Production by Synthetic Biology

Engineered plant cell lines have the potential to achieve enhanced metabolite production rates, providing a high-yielding source of compounds of interest. Improving the production of taxanes, pharmacologically valuable secondary metabolites of Taxus spp., is hindered by an incomplete knowledge of the taxane biosynthetic pathway. Of the five unknown steps, three are thought to involve cytochrome P450-like hydroxylases. In the current work, after an in-depth in silico characterization of four candidate enzymes proposed in a previous cDNA-AFLP assay, TB506 was selected as a candidate for the hydroxylation of the taxane side chain. A docking assay indicated TB506 is active after the attachment of the side chain based on its affinity to the ligand 3'N-dehydroxydebenzoyltaxol. Finally, the involvement of TB506 in the last hydroxylation step of the paclitaxel biosynthetic pathway was confirmed by functional assays. The identification of this hydroxylase will contribute to the development of alternative sustainable paclitaxel production systems using synthetic biology techniques.

Functional expression and characterization of cinnamic acid 4-hydroxylase from the hornwort Anthoceros agrestis in Physcomitrella patens

Cinnamic acid 4-hydroxylase from the hornwort Anthoceros agrestis (AaC4H) was functionally expressed in the moss Physcomitrella patens and characterized at biochemical and molecular levels. Cinnamic acid 4-hydroxylase (C4H), a cytochrome P450-dependent hydroxylase, catalyzes the formation of 4-coumaric acid (=4-hydroxycinnamic acid) from trans-cinnamic acid. In the hornwort Anthoceros agrestis (Aa), this enzyme is supposed to be involved in the biosynthesis of rosmarinic acid (a caffeic acid ester of 3-(3,4-dihydroxyphenyl)lactic acid) and other related compounds. The coding sequence of AaC4H (CYP73A260) was expressed in the moss Physcomitrella patens (Pp_AaC4H). Protein extracts from the transformed moss showed considerably increased C4H activity driven by NADPH:cytochrome P450 reductase of the moss. Since Physcomitrella has own putative cinnamic acid 4-hydroxylases, enzyme characterization was carried out in parallel with the untransformed Physcomitrella wild type (Pp_WT). Apparent K_m-values for cinnamic acid and NADPH were determined to be at 17.3 µM and 88.0 µM for Pp_AaC4H and 25.1 µM and 92.3 µM for Pp_WT, respectively. Expression levels of AaC4H as well as two Physcomitrella patens C4H isoforms were analyzed by quantitative real-time PCR. While PpC4H_1 displayed constantly low levels of expression during the whole 21-day culture period, AaC4H and PpC4H_2 increased their expression during the first 6-8 days of the culture period and then decreased again. This work describes the biochemical in vitro characterization of a cytochrome P450-dependent enzyme, namely C4H, heterologously expressed in the haploid model plant Physcomitrella patens.

Functional expression and characterization of cinnamic acid 4-hydroxylase from the hornwort Anthoceros agrestis in Physcomitrella patens

Cinnamic acid 4-hydroxylase from the hornwort Anthoceros agrestis (AaC4H) was functionally expressed in the moss Physcomitrella patens and characterized at biochemical and molecular levels. Cinnamic acid 4-hydroxylase (C4H), a cytochrome P450-dependent hydroxylase, catalyzes the formation of 4-coumaric acid (=4-hydroxycinnamic acid) from trans-cinnamic acid. In the hornwort Anthoceros agrestis (Aa), this enzyme is supposed to be involved in the biosynthesis of rosmarinic acid (a caffeic acid ester of 3-(3,4-dihydroxyphenyl)lactic acid) and other related compounds. The coding sequence of AaC4H (CYP73A260) was expressed in the moss Physcomitrella patens (Pp_AaC4H). Protein extracts from the transformed moss showed considerably increased C4H activity driven by NADPH:cytochrome P450 reductase of the moss. Since Physcomitrella has own putative cinnamic acid 4-hydroxylases, enzyme characterization was carried out in parallel with the untransformed Physcomitrella wild type (Pp_WT). Apparent K_m-values for cinnamic acid and NADPH were determined to be at 17.3 µM and 88.0 µM for Pp_AaC4H and 25.1 µM and 92.3 µM for Pp_WT, respectively. Expression levels of AaC4H as well as two Physcomitrella patens C4H isoforms were analyzed by quantitative real-time PCR. While PpC4H_1 displayed constantly low levels of expression during the whole 21-day culture period, AaC4H and PpC4H_2 increased their expression during the first 6-8 days of the culture period and then decreased again. This work describes the biochemical in vitro characterization of a cytochrome P450-dependent enzyme, namely C4H, heterologously expressed in the haploid model plant Physcomitrella patens.

The Major Factors Causing the Microspore Abortion of Genic Male Sterile Mutant NWMS1 in Wheat (Triticum aestivum L.)

Male sterility is a valuable trait for genetic research and production application of wheat (Triticum aestivum L.). NWMS1, a novel typical genic male sterility mutant, was obtained from Shengnong 1, mutagenized with ethyl methane sulfonate (EMS). Microstructure and ultrastructure observations of the anthers and microspores indicated that the pollen abortion of NWMS1 started at the early uninucleate microspore stage. Pollen grain collapse, plasmolysis, and absent starch grains were the three typical characteristics of the abnormal microspores. The anther transcriptomes of NWMS1 and its wild type Shengnong 1 were compared at the early anther development stage, pollen mother cell meiotic stage, and binucleate microspore stage. Several biological pathways clearly involved in abnormal anther development were identified, including protein processing in endoplasmic reticulum, starch and sucrose metabolism, lipid metabolism, and plant hormone signal transduction. There were 20 key genes involved in the abnormal anther development, screened out by weighted gene co-expression network analysis (WGCNA), including SKP1B, BIP5, KCS11, ADH3, BGLU6, and TIFY10B. The results indicated that the defect in starch and sucrose metabolism was the most important factor causing male sterility in NWMS1. Based on the experimental data, a primary molecular regulation model of abnormal anther and pollen developments in mutant NWMS1 was established. These results laid a solid foundation for further research on the molecular mechanism of wheat male sterility.

Transcriptomic analysis reveals potential genes involved in tanshinone biosynthesis in Salvia miltiorrhiza

Tanshinones are important bioactive components in Salvia miltiorrhiza and mainly accumulate in the periderms of mature roots. Tanshinone biosynthesis is a complicated process, and little is known about the third stage of the pathway. To investigate potential genes that are responsible for tanshinone biosynthesis, we conducted transcriptome profiling analysis of two S. miltiorrhiza cultivars. Differential expression analysis provided 2,149 differentially expressed genes (DEGs) for further analysis. GO and KEGG analysis showed that the DEGs were mainly associated with the biosynthesis of secondary metabolites. Weighted gene coexpression network analysis (WGCNA) was further performed to identify a “cyan” module associated with tanshinone biosynthesis. In this module, 25 cytochromes P450 (CYPs), three 2-oxoglutarate-dependent dioxygenases (2OGDs), one short-chain alcohol dehydrogenases (SDRs) and eight transcription factors were found to be likely involved in tanshinone biosynthesis. Among these CYPs, 14 CYPs have been reported previously, and 11 CYPs were identified in this study. Expression analysis showed that four newly identified CYPs were upregulated upon application of MeJA, suggesting their possible roles in tanshinone biosynthesis. Overall, this study not only identified candidate genes involved in tanshinone biosynthesis but also provided a basis for characterization of genes involved in important active ingredients of other traditional Chinese medicinal plants.

Deep expression analysis reveals distinct cold-response strategies in rubber tree (Hevea brasiliensis)

Background

Natural rubber, an indispensable commodity used in approximately 40,000 products, is fundamental to the tire industry. The rubber tree species Hevea brasiliensis (Willd. ex Adr. de Juss.) Muell-Arg., which is native the Amazon rainforest, is the major producer of latex worldwide. Rubber tree breeding is time consuming, expensive and requires large field areas. Thus, genetic studies could optimize field evaluations, thereby reducing the time and area required for these experiments. In this work, transcriptome sequencing was used to identify a full set of transcripts and to evaluate the gene expression involved in the different cold-response strategies of the RRIM600 (cold-resistant) and GT1 (cold-tolerant) genotypes.

Results

We built a comprehensive transcriptome using multiple database sources, which resulted in 104,738 transcripts clustered in 49,304 genes. The RNA-seq data from the leaf tissues sampled at four different times for each genotype were used to perform a gene-level expression analysis. Differentially expressed genes (DEGs) were identified through pairwise comparisons between the two genotypes for each time series of cold treatments.

DEG annotation revealed that RRIM600 and GT1 exhibit different chilling tolerance strategies. To cope with cold stress, the RRIM600 clone upregulates genes promoting stomata closure, photosynthesis inhibition and a more efficient reactive oxygen species (ROS) scavenging system. The transcriptome was also searched for putative molecular markers (single nucleotide polymorphisms (SNPs) and microsatellites) in each genotype. and a total of 27,111 microsatellites and 202,949 (GT1) and 156,395 (RRIM600) SNPs were identified in GT1 and RRIM600. Furthermore, a search for alternative splicing (AS) events identified a total of 20,279 events.

Conclusions

The elucidation of genes involved in different chilling tolerance strategies associated with molecular markers and information regarding AS events provides a powerful tool for further genetic and genomic analyses of rubber tree breeding.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5852-5) contains supplementary material, which is available to authorized users.

Identification of genes associated with stress tolerance in moth bean [Vigna aconitifolia (Jacq.) Marechal], a stress hardy crop

Moth bean is the most drought and heat tolerant cultigens among Asian Vigna. We performed comparative transcriptome analysis of moth bean cultivar "Marumoth" under control and stress condition. De novo transcriptome assembly was carried out by using Velvet followed by Oases softwares. Differential expression analyses, SSR identification and validation and mapping of pathways and transcription factors were conducted. A total of 179,979 and 201,888 reads were generated on Roche 454 platform and 48,617,205 and 45,449,053 reads were generated on ABI Solid platform for the control and stressed samples. Combined assembly from Roche and ABI Solid platforms generated 16,090 and 15,096 transcripts for control and stressed samples. We found 1287 SSRs and 5606 transcripts involved in 179 pathways. The 55 transcription factor families represented 19.42% of total mothbean transcripts. In expression profiling, ten transcripts were found to be up-regulated and 41 down-regulated while 490 showed no major change under moisture stress condition. Stress inducible genes like Catalase, Cyt P450 monooxygenase, heat shock proteins (HSP 90 and HSP 70), oxidoreductase, protein kinases, dehydration responsive protein (DRP), universal stress protein and ferridoxin NADH oxidoreductase genes were up-regulated in stressed sample. Genes which might be involved in moisture stress tolerance in moth bean were identified and these might be useful for stress tolerance breeding in moth bean and other related crops.

Molecular elucidation of a new allelic variation at the Sg-5 gene associated with the absence of group A saponins in wild soybean

In soybean, triterpenoid saponin is one of the major secondary metabolites and is further classified into group A and DDMP saponins. Although they have known health benefits for humans and animals, acetylation of group A saponins causes bitterness and gives an astringent taste to soy products. Therefore, several studies are being conducted to eliminate acetylated group A saponins. Previous studies have isolated and characterized the Sg-5 (Glyma.15g243300) gene, which encodes the cytochrome P450 72A69 enzyme and is responsible for soyasapogenol A biosynthesis. In this study, we elucidated the molecular identity of a novel mutant of Glycine soja, 'CWS5095'. Phenotypic analysis using TLC and LC-PDA/MS/MS showed that the mutant 'CWS5095' did not produce any group A saponins. Segregation analysis showed that the absence of group A saponins is controlled by a single recessive allele. The locus was mapped on chromosome 15 (4.3 Mb) between Affx-89193969 and Affx-89134397 where the previously identified Glyma.15g243300 gene is positioned. Sequence analysis of the coding region for the Glyma.15g243300 gene revealed the presence of four SNPs in 'CWS5095' compared to the control lines. One of these four SNPs (G1127A) leads to the amino acid change Arg376Lys in the EXXR motif, which is invariably conserved among the CYP450 superfamily proteins. Co-segregation analysis showed that the missense mutation (Arg376Lys) was tightly linked with the absence of group A saponins in 'CWS5095'. Even though Arg and Lys have similar chemical features, the 3D modelled protein structure indicates that the replacement of Arg with Lys may cause a loss-of-function of the Sg-5 protein by inhibiting the stable binding of a heme cofactor to the CYP72A69 apoenzyme.

Quantitative Trait Locus Mapping and Candidate Gene Analysis for Verticillium Wilt Resistance Using Gossypium barbadense Chromosomal Segment Introgressed Line

Verticillium wilt (VW) is a soil-borne fungal disease that is caused by Verticillium dahliae Kleb and seriously damages cotton production annually in China. To date, many efforts have been made to improve the resistance of upland cotton against VW, but little progress has been achieved because of a lack of resistant upland cotton to VW. G. barbadense is known to carry high resistance to VW; however, it is difficult to transfer the resistance trait from G. barbadense to upland cotton because of linkage drag and distortion in the interspecific hybrid. In this study, a chromosomal segment introgression line (CSIL), SuVR043, containing a single and homozygous chromosome segment of G. barbadense cv. H7124 D04 (Chr 22), was created and used to construct an F₂ population for mapping of VW resistance quantitative trait loci (QTLs) in the greenhouse. Two major resistance QTLs against nondefoliating V. dahliae isolate Bp2, called qVW-Bp2-1 and qVW-Bp2-2, which were flanked by the markers cgr6409-ZHX37 and ZHX57-ZHX70 and explained an average of 16.38 and 22.36% of the observed phenotypic variation, respectively, were detected in three independent replicate experiments. The genetic distances from cgr6409 to ZHX37 and from ZHX57 to ZHX70 were 2.4 and 0.8 cM, respectively. By analyzing the genome sequence of the qVW-Bp2-1 and qVW-Bp2-2 regions, we determined that the accurate physical distances from cgr6409 to ZHX37 and from ZHX57 to ZHX70 in the G. barbadense genome are 254 and 140 kb, and that those spans 36 and 20 putative genes, respectively. The results of the expression analysis showed significant differences in the expression profiles of GbCYP450, GbTMEM214, and GbRLK among G. barbadense cv. H7124, CSIL SuVR043 and G. hirsutum acc. Sumian 8 at different times after inoculation with V. dahliae isolate Bp2. Virus-induced gene silencing (VIGS) analysis showed that silencing of GbCYP450 and GbTMEM214 decreased H7124 and CSIL SuVR043 resistance to VW. These results form a solid foundation for fine mapping and cloning of resistance genes in the substituted segment and will provide valuable assistance in future efforts to breed for VW resistance.

Advanced Proteomic Approaches to Elucidate Somatic Embryogenesis

Somatic embryogenesis (SE) is a cell differentiation process by which a somatic cell changes its genetic program and develops into an embryonic cell. Investigating this process with various explant sources in vitro has allowed us to trace somatic embryo development from germination to plantlets and has led to the generation of new technologies, including genetic transformation, endangered species conservation, and synthetic seed production. A transcriptome data comparison from different stages of the developing somatic embryo has revealed a complex network controlling the somatic cell's fate, suggesting that an interconnected network acts at the protein level. Here, we discuss the current progress on SE using proteomic-based data, focusing on changing patterns of proteins during the establishment of the somatic embryo. Despite the advanced proteomic approaches available so far, deciphering how the somatic embryo is induced is still in its infancy. The new proteomics techniques that lead to the quantification of proteins with different abundances during the induction of SE are opening this area of study for the first time. These quantitative differences can elucidate the different pathways involved in SE induction. We envisage that the application of these proteomic technologies can be pivotal to identifying proteins critical to the process of SE, demonstrating the cellular localization, posttranslational modifications, and turnover protein events required to switch from a somatic cell to a somatic embryo cell and providing new insights into the molecular mechanisms underlying SE. This work will help to develop biotechnological strategies for mass production of quality crop material.

ABNORMAL POLLEN VACUOLATION1 (APV1) is required for male fertility by contributing to anther cuticle and pollen exine formation in maize

Anther cuticle and pollen exine are the major protective barriers against various stresses. The proper functioning of genes expressed in the tapetum is vital for the development of pollen exine and anther cuticle. In this study, we report a tapetum-specific gene, Abnormal Pollen Vacuolation1 (APV1), in maize that affects anther cuticle and pollen exine formation. The apv1 mutant was completely male sterile. Its microspores were swollen, less vacuolated, with a flat and empty anther locule. In the mutant, the anther epidermal surface was smooth, shiny, and plate-shaped compared with the three-dimensional crowded ridges and randomly formed wax crystals on the epidermal surface of the wild-type. The wild-type mature pollen had elaborate exine patterning, whereas the apv1 pollen surface was smooth. Only a few unevenly distributed Ubisch bodies were formed on the apv1 mutant, leading to a more apparent inner surface. A significant reduction in the cutin monomers was observed in the mutant. APV1 encodes a member of the P450 subfamily, CYP703A2-Zm, which contains 530 amino acids. APV1 appeared to be widely expressed in the tapetum at the vacuolation stage, and its protein signal co-localized with the endoplasmic reticulum (ER) signal. RNA-Seq data revealed that most of the genes in the fatty acid metabolism pathway were differentially expressed in the apv1 mutant. Altogether, we suggest that APV1 functions in the fatty acid hydroxylation pathway which is involved in forming sporopollenin precursors and cutin monomers that are essential for the development of pollen exine and anther cuticle in maize.

De novo transcriptome assembly analysis of weed Apera spica-venti from seven tissues and growth stages

BACKGROUND

Loose silky bentgrass (Apera spica-venti) is an important weed in Europe with a recent increase in herbicide resistance cases. The lack of genetic information about this noxious weed limits its biological understanding such as growth, reproduction, genetic variation, molecular ecology and metabolic herbicide resistance. This study produced a reference transcriptome for A. spica-venti from different tissues (leaf, root, stem) and various growth stages (seed at phenological stages 05, 07, 08, 09). The de novo assembly was performed on individual and combined dataset followed by functional annotations. Individual transcripts and gene families involved in metabolic based herbicide resistance were identified.

RESULTS

Eight separate transcriptome assemblies were performed and compared. The combined transcriptome assembly consists of 83,349 contigs with an N50 and average contig length of 762 and 658 bp, respectively. This dataset contains 74,724 transcripts consisting of total 54,846,111 bp. Among them 94% had a homologue to UniProtKB, 73% retrieved a GO mapping, and 50% were functionally annotated. Compared with other grass species, A. spica-venti has 26% proteins in common to Brachypodium distachyon, and 41% to Lolium spp. Glycosyltransferases had the highest number of transcripts in each tissue followed by the cytochrome P450s. The GSTF1 and CYP89A2 transcripts were recovered from the majority of tissues and aligned at a maximum of 66 and 30% to proven herbicide resistant allele from Alopecurus myosuroides and Lolium rigidum, respectively.

CONCLUSIONS

De novo transcriptome assembly enabled the generation of the first reference transcriptome of A. spica-venti. This can serve as stepping stone for understanding the metabolic herbicide resistance as well as the general biology of this problematic weed. Furthermore, this large-scale sequence data is a valuable scientific resource for comparative transcriptome analysis for Poaceae grasses.

Integrated RNA-seq and sRNA-seq analysis reveals miRNA effects on secondary metabolism in Solanum tuberosum L

Light is a major environmental factor that affects metabolic pathways and stimulates the production of secondary metabolites in potato. However, adaptive changes in potato metabolic pathways and physiological functions triggered by light are partly explained by gene expression changes. Regulation of secondary metabolic pathways in potato has been extensively studied at transcriptional level, but little is known about the mechanisms of post-transcriptional regulation by miRNAs. To identify light-responsive miRNAs/mRNAs and construct putative metabolism pathways regulated by the miRNA-mRNA pairs, an integrated omics (sRNAome and transcriptome) analysis was performed to potato under light stimulus. A total of 31 and 48 miRNAs were identified to be differentially expressed in the leaves and tubers, respectively. Among the DEGs, 1353 genes in the leaves and 1841 genes in the tubers were upregulated, while 1595 genes in the leaves and 897 genes in the tubers were downregulated by light. Mapman enrichment analyses showed that genes related to MVA pathway, alkaloids-like, phenylpropanoids, flavonoids, and carotenoids metabolism were significantly upregulated, while genes associated with major CHO metabolism were repressed in the leaves and tubers. Integrated miRNA and mRNA profiles revealed that light-responsive miRNAs are important regulators in alkaloids metabolism, UMP salvage, lipid biosynthesis, and cellulose catabolism. Moreover, several miRNAs may participate in glycoalkaloids metabolism via JA signaling pathway, UDP-glucose biosynthesis and hydroxylation reaction. This study provides a global view of miRNA and mRNA expression profiles in potato response to light, our results suggest that miRNAs might play important roles in secondary metabolic pathways, especially in glycoalkaloid biosynthesis. The findings will enlighten us on the genetic regulation of secondary metabolite pathways and pave the way for future application of genetically engineered potato.

Diversification of fruit shape in the Brassicaceae family

Diversity in fruit shape. Angiosperms (flowering plants) evolved during the Cretaceous Period more than 100 million years ago and quickly colonized all terrestrial habitats on the planet. A major reason for their success was the formation of fruits that would protect and nurture the developing seeds. Moreover, a massive range of diversity in fruit shape occurred during a relatively short time, which allowed for the development of ingenious ways of fertilization as well as strategies for efficient seed dispersal. The Brassicaceae family more than any exemplifies the diversity in fruit morphologies, thus providing an ideal group of plants to study how specific shapes are established. Although many genes controlling fruit patterning in the model plant Arabidopsis thaliana have been identified, the processes of carpel and fruit morphogenesis are still poorly understood. Moreover, Arabidopsis fruits are relatively simple in their structure and are therefore not ideally suited for analyzing processes of morphology determination without comparison to species with differently shaped fruits. Here, we review the diversity of fruit shape within the Brassicaceae family. As an example we describe the close relative of Arabidopsis, Capsella rubella that develops flat, heart-shaped fruits showing and highlighting its potential as a model system for research into organ shape. Recent progress in genomics including fast and cheap genome sequencing and annotation as well as development of mutant populations has opened entirely new and exciting possibilities of studying the mechanisms and processes underlying fruit formation in angiosperms.

Genome-Wide Association Study for Traits Related to Plant and Grain Morphology, and Root Architecture in Temperate Rice Accessions

BACKGROUND

In this study we carried out a genome-wide association analysis for plant and grain morphology and root architecture in a unique panel of temperate rice accessions adapted to European pedo-climatic conditions. This is the first study to assess the association of selected phenotypic traits to specific genomic regions in the narrow genetic pool of temperate japonica. A set of 391 rice accessions were GBS-genotyped yielding-after data editing-57000 polymorphic and informative SNPS, among which 54% were in genic regions.

RESULTS

In total, 42 significant genotype-phenotype associations were detected: 21 for plant morphology traits, 11 for grain quality traits, 10 for root architecture traits. The FDR of detected associations ranged from 3 · 10-7 to 0.92 (median: 0.25). In most cases, the significant detected associations co-localised with QTLs and candidate genes controlling the phenotypic variation of single or multiple traits. The most significant associations were those for flag leaf width on chromosome 4 (FDR = 3 · 10-7) and for plant height on chromosome 6 (FDR = 0.011).

CONCLUSIONS

We demonstrate the effectiveness and resolution of the developed platform for high-throughput phenotyping, genotyping and GWAS in detecting major QTLs for relevant traits in rice. We identified strong associations that may be used for selection in temperate irrigated rice breeding: e.g. associations for flag leaf width, plant height, root volume and length, grain length, grain width and their ratio. Our findings pave the way to successfully exploit the narrow genetic pool of European temperate rice and to pinpoint the most relevant genetic components contributing to the adaptability and high yield of this germplasm. The generated data could be of direct use in genomic-assisted breeding strategies.

Functional expression of a putative geraniol 8-hydroxylase by reconstitution of bacterially expressed plant CYP76F45 and NADPH-cytochrome P450 reductase CPR I from Croton stellatopilosus Ohba

While attempting to isolate the enzyme geranylgeraniol 18-hydroxylase, which is involved in plaunotol biosynthesis in Croton stellatopilosus (Cs), the cDNAs for a cytochrome P450 monooxygenase(designated as CYP76F45) and an NADPH-cytochrome P450 reductase (designated as CPR I based on its classification) were isolated from the leaf. The CYP76F45 and CsCPR I genes have open reading frames (ORFs) encoding 507- and 711-amino acid proteins with predicted relative molecular weights of 56.7 and 79.0 kDa,respectively. Amino acid sequence comparison showed that both CYP76F45 (63–73%) and CsCPR I (79–83%) share relatively high sequence identities with homologous proteins in other plant species.Phylogenetic tree analysis confirmed that CYP76F45 belongs to the CYP76 family and that CsCPR I belongs to Class I of dicotyledonous CPRs, with both being closely related to Ricinus communis genes. Functional characterization of both enzymes, each expressed separately in Escherichia coli as recombinant proteins,showed that only simultaneous incubation of the membrane bound proteins with the substrate geraniol (GOH) and the coenzyme NADPH could form 8-hydroxygeraniol. The enzyme mixture could also utilize acyclic sesquiterpene farnesol (FOH) with a comparable substrate preference ratio (GOH:FOH) of 54:46. The levelsof the CYP76F45 and CsCPR I transcripts in the shoots, leaves and twigs of C. stellatopilosus were correlated with the levels of a major monoterpenoid indole alkaloid, identified tentatively as 19-Evallesamine,that accumulated in these plant parts. These results suggested that CYP76F45 and CPR I function as the enzyme geraniol-8-hydroxylase (G8H), which is likely to be involved in the biosynthesis of the indole alkaloid in C. stellatopilosus [corrected].

A cytochrome P450, OsDSS1, is involved in growth and drought stress responses in rice (Oryza sativa L.)

Cytochrome P450s are among the largest protein coding gene families in plant genomes. However, majority of the genes remain uncharacterized. Here, we report the characterization of dss1, a rice mutant showing dwarfism and reduced grain size. The dss1 phenotype is caused by a non-synonymous point mutation we identified in DSS1, which is member of a P450 gene cluster located on rice chromosome 3 and corresponds to the previously reported CYP96B4/SD37 gene. Phenotypes of several dwarf mutants characterized in rice are associated with defects in the biosynthesis or perception of the phytohormones gibberellins (GAs) and brassinosteroids (BRs). However, both GA and BR failed to rescue the dss1 phenotype. Hormone profiling revealed the accumulation of abscisic acid (ABA) and ABA metabolites, as well as significant reductions in GA19 and GA53 levels, precursors of the bioactive GA1, in the mutant. The dss1 contents of cytokinin and auxins were not significantly different from wild-type plants. Consistent with the accumulation of ABA and metabolites, germination and early growth was delayed in dss1, which also exhibited an enhanced tolerance to drought. Additionally, expressions of members of the DSS1/CYP96B gene cluster were regulated by drought stress and exogenous ABA. RNA-seq-based transcriptome profiling revealed, among others, that cell wall-related genes and genes involved in lipid metabolism were up- and down-regulated in dss1, respectively. Taken together, these findings suggest that DSS1 mediates growth and stress responses in rice by fine-tuning GA-to-ABA balance, and might as well play a role in lipid metabolism.

Involvement of Iron-Containing Proteins in Genome Integrity in Arabidopsis Thaliana

The Arabidopsis genome encodes numerous iron-containing proteins such as iron-sulfur (Fe-S) cluster proteins and hemoproteins. These proteins generally utilize iron as a cofactor, and they perform critical roles in photosynthesis, genome stability, electron transfer, and oxidation-reduction reactions. Plants have evolved sophisticated mechanisms to maintain iron homeostasis for the assembly of functional iron-containing proteins, thereby ensuring genome stability, cell development, and plant growth. Over the past few years, our understanding of iron-containing proteins and their functions involved in genome stability has expanded enormously. In this review, I provide the current perspectives on iron homeostasis in Arabidopsis, followed by a summary of iron-containing protein functions involved in genome stability maintenance and a discussion of their possible molecular mechanisms.

Abiotic stress and genome dynamics: specific genes and transposable elements response to iron excess in rice

BACKGROUND

Iron toxicity is a root related abiotic stress, occurring frequently in flooded soils. It can affect the yield of rice in lowland production systems. This toxicity is associated with high concentrations of reduced iron (Fe(2+)) in the soil solution. Although the first interface of the element is in the roots, the consequences of an excessive uptake can be observed in several rice tissues. In an original attempt to find both genes and transposable elements involved in the response to an iron toxicity stress, we used a microarray approach to study the transcriptional responses of rice leaves of cv. Nipponbare (Oryza sativa L. ssp. japonica) to iron excess in nutrient solution.

RESULTS

A large number of genes were significantly up- or down-regulated in leaves under the treatment. We analyzed the gene ontology and metabolic pathways of genes involved in the response to this stress and the cis-regulatory elements (CREs) present in the promoter region of up-regulated genes. The majority of genes act in the pathways of lipid metabolic process, carbohydrate metabolism, biosynthesis of secondary metabolites and plant hormones. We also found genes involved in iron acquisition and mobilization, transport of cations and regulatory mechanisms for iron responses, and in oxidative stress and reactive oxygen species detoxification. Promoter regions of 27% of genes up-regulated present at least one significant occurrence of an ABA-responsive CRE. Furthermore, and for the first time, we were able to show that iron stress triggers the up-regulation of many LTR-retrotransposons. We have established a complete inventory of transposable elements transcriptionally activated under iron excess and the CREs which are present in their LTRs.

CONCLUSION

The short-term response of Nipponbare seedlings to iron excess, includes activation of genes involved in iron homeostasis, in particular transporters, transcription factors and ROS detoxification in the leaves, but also many transposable elements. Our data led to the identification of CREs which are associated with both genes and LTR-retrotransposons up-regulated under iron excess. Our results strengthen the idea that LTR-retrotransposons participate in the transcriptional response to stress and could thus confer an adaptive advantage for the plant.

Molecular cloning, bacterial expression and functional characterisation of cytochrome P450 monooxygenase, CYP97C27, and NADPH-cytochrome P450 reductase, CPR I, from Croton stellatopilosus Ohba

The cDNAs for cytochrome P450 monooxygenase (designated as CYP97C27 by D. Nelson's group) and NADPH-cytochrome P450 reductase (designated as CPR I based on its classification) were isolated from Croton stellatopilosus leaves, which actively biosynthesise plaunotol (18-OH geranylgeraniol). CYP97C27 and CPR I contain open reading frames encoding proteins of 471 and 711 amino acids with predicted molecular masses of 53 and 79kDa, respectively. By aligning the deduced sequences of CYP97C27 and CPR I with other plant species, all functional domains of CYP97C27 (heme and oxygen binding) and CPR I (CYP- and FMN, FAD, and NADPH cofactor binding) were identified. Amino acid sequence comparison indicated that both CYP97C27 (85-93%) and CPR I (79-83%) share high sequence identities with homologous proteins in other plant species, suggesting that CYP97C27 belongs to the CYP97C subfamily and that CPR I belongs to class I of the dicotyledonous CPR. Functional characterisation of both enzymes, produced in Escherichia coli (pET32a/BL21(DE3)) as recombinant proteins, showed that simultaneous incubation of CYP97C27 and CPR I with the substrate geranylgeraniol (GGOH) and coenzyme NADPH led to formation of the product plaunotol. In C. stellatopilosus, the levels of the CYP97C27 and CPR I transcripts were highly correlated with those of several mRNAs involved in the plaunotol biosynthetic pathway, suggesting that CYP97C27 and CPR I are the enzymes that catalyse the last hydroxylation step of the pathway.

Transcriptome sequencing of transgenic poplar (Populus × euramericana 'Guariento') expressing multiple resistance genes

Background

Transgenic poplar (Populus × euramericana 'Guariento') plants harboring five exogenous, stress-related genes exhibit increased tolerance to multiple stresses including drought, salt, waterlogging, and insect feeding, but the complex mechanisms underlying stress tolerance in these plants have not been elucidated. Here, we analyzed the differences in the transcriptomes of the transgenic poplar line D5-20 and the non-transgenic line D5-0 using high-throughput transcriptome sequencing techniques and elucidated the functions of the differentially expressed genes using various functional annotation methods.

Results

We generated 11.80 Gb of sequencing data containing 63, 430, 901 sequences, with an average length of 200 bp. The processed sequences were mapped to reference genome sequences of Populus trichocarpa. An average of 62.30% and 61.48% sequences could be aligned with the reference genomes for D5-20 and D5-0, respectively. We detected 11,352 (D5-20) and 11,372 expressed genes (D5-0), 7,624 (56.61%; D5-20) and 7,453 (65.54%; D5-0) of which could be functionally annotated. A total of 782 differentially expressed genes in D5-20 were identified compared with D5-0, including 628 up-regulated and 154 down-regulated genes. In addition, 196 genes with putative functions related to stress responses were also annotated. Gene Ontology (GO) analysis revealed that 346 differentially expressed genes are mainly involved in 67 biological functions, such as DNA binding and nucleus. KEGG annotation revealed that 36 genes (21 up-regulated and 15 down-regulated) were enriched in 51 biological pathways, 9 of which are linked to glucose metabolism. KOG functional classification revealed that 475 genes were enriched in 23 types of KOG functions.

Conclusion

These results suggest that the transferred exogenous genes altered the expression of stress (biotic and abiotic) response genes, which were distributed in different metabolic pathways and were linked to some extent. Our results provide a theoretic basis for investigating the functional mechanisms of exogenous genes in transgenic plants.

Research progress relating to the role of cytochrome P450 in the biosynthesis of terpenoids in medicinal plants

Terpenoids are an extensive and diverse group of plant secondary metabolites. To date, they have been applied in many fields including industry, medicine and health. The wide variety of terpenoid compounds cannot arise solely from simple cyclisations of a precursor molecule or from a single-step reaction; their structural diversity depends on the modification of many specific chemical groups, rearrangements of their skeletal structures and on the post-modification reactions. Most of the post-modification enzymes that catalyse these reactions are cytochrome P450 monooxygenases. Therefore, the discovery and identification of plant P450 genes plays a vital role in the exploration of terpenoid biosynthesis pathways. This review summarises recent research progress relating to the function of plant cytochrome P450 enzymes, describes P450 genes that have been cloned from full-length cDNA and identifies the function of P450 enzymes in the terpenoid biosynthesis pathways of several medicinal plants.

CYP709B3, a cytochrome P450 monooxygenase gene involved in salt tolerance in Arabidopsis thaliana

BACKGROUND

Within the Arabidopsis genome, there are 272 cytochrome P450 monooxygenase (P450) genes. However, the biological functions of the majority of these P450s remain unknown. The CYP709B family of P450s includes three gene members, CYP709B1, CYP709B2 and CYP709B3, which have high amino acid sequence similarity and lack reports elucidating biological functions.

RESULTS

We identified T-DNA insertion-based null mutants of the CYP709B subfamily of genes. No obvious morphological phenotypes were exhibited under normal growth conditions. When the responses to ABA and salt stress were studied in these mutants, only the cyp709b3 mutant showed sensitivity to ABA and salt during germination. Under moderate salt treatment (150 mM NaCl), cyp709b3 showed a higher percentage of damaged seedlings, indicating a lower tolerance to salt stress. CYP709B3 was highly expressed in all analyzed tissues and especially high in seedlings and leaves. In contrast, CYP709B1 and CYP709B2 were highly expressed in siliques, but were at very low levels in other tissues. Under salt stress condition, CYP709B3 gene expression was induced after 24 hr and remained at high expression level. Expression of the wild type CYP709B3 gene in the cyp709b3 mutant fully complemented the salt intolerant phenotype. Furthermore, metabolite profiling analysis revealed some differences between wild type and cyp709b3 mutant plants, supporting the salt intolerance phenotype of the cyp709b3 mutant.

CONCLUSIONS

These results suggest that CYP709B3 plays a role in ABA and salt stress response and provides evidence to support the functions of cytochrome P450 enzymes in plant stress response.

Molecular cloning and characterization of a cytochrome P450 in sanguinarine biosynthesis from Eschscholzia californica cells

Benzophenanthridine alkaloids, such as sanguinarine, are produced from reticuline, a common intermediate in benzylisoquinoline alkaloid biosynthesis, via protopine. Four cytochrome P450s are involved in the biosynthesis of sanguinarine from reticuline; i.e. cheilanthifoline synthase (CYP719A5; EC 1.14.21.2.), stylopine synthase (CYP719A2/A3; EC 1.14.21.1.), N-methylstylopine hydroxylase (MSH) and protopine 6-hydroxylase (P6H; EC 1.14.13.55.). In this study, a cDNA of P6H was isolated from cultured Eschscholzia californica cells, based on an integrated analysis of metabolites and transcript expression profiles of transgenic cells with Coptis japonica scoulerine-9-O-methyltransferase. Using the full-length candidate cDNA for P6H (CYP82N2v2), recombinant protein was produced in Saccharomyces cerevisiae for characterization. The microsomal fraction containing recombinant CYP82N2v2 showed typical reduced CO-difference spectra of P450, and production of dihydrosanguinarine and dihydrochelerythrine from protopine and allocryptopine, respectively. Further characterization of the substrate-specificity of CYP82N2v2 indicated that 6-hydroxylation played a role in the reaction.

Cytochrome P450 CYP78A9 is involved in Arabidopsis reproductive development

Synchronized communication between gametophytic and sporophytic tissue is crucial for successful reproduction, and hormones seem to have a prominent role in it. Here, we studied the role of the Arabidopsis (Arabidopsis thaliana) cytochrome P450 CYP78A9 enzyme during reproductive development. First, controlled pollination experiments indicate that CYP78A9 responds to fertilization. Second, while CYP78A9 overexpression can uncouple fruit development from fertilization, the cyp78a8 cyp78a9 loss-of-function mutant has reduced seed set due to outer ovule integument development arrest, leading to female sterility. Moreover, CYP78A9 has a specific expression pattern in inner integuments in early steps of ovule development as well as in the funiculus, embryo, and integuments of developing seeds. CYP78A9 overexpression did not change the response to the known hormones involved in flower development and fruit set, and it did not seem to have much effect on the major known hormonal pathways. Furthermore, according to previous predictions, perturbations in the flavonol biosynthesis pathway were detected in cyp78a9, cyp78a8 cyp78a9, and empty siliques (es1-D) mutants. However, it appeared that they do not cause the observed phenotypes. In summary, these results add new insights into the role of CYP78A9 in plant reproduction and present, to our knowledge, the first characterization of metabolite differences between mutants in this gene family.

Comparative RNA-seq analysis of early-infected peach leaves by the invasive phytopathogen Xanthomonas arboricola pv. pruni

Xanthomonas arboricola pv. pruni is a quarantine bacterial pathogen that threatens peach production by causing necrotic spots on leaves and fruits, thus with the potential of severely reducing yields. The current understanding of the host plant defense responses to the pathogen is very limited. Using whole transcriptome sequencing, differential gene expression was analyzed at two time points, 2 h and 12 h post inoculation (hpi), by comparing the inoculated samples to their respective controls. On the total of 19,781 known peach genes that were expressed in all time points and conditions, 34 and 263 were differentially expressed at 2 and 12 hpi, respectively. Of those, 82% and 40% were up-regulated, respectively; and 18% and 60% were down-regulated, respectively. The functional annotation based on gene ontology (GO) analysis highlighted that genes involved in metabolic process and response to stress were particularly represented at 2 hpi whereas at 12 hpi cellular and metabolic processes were the categories with the highest number of genes differentially expressed. Of particular interest among the differentially expressed genes identified were several pathogen-associated molecular pattern (PAMP) receptors, disease resistance genes including several RPM1-like and pathogenesis related thaumatin encoding genes. Other genes involved in photosynthesis, in cell wall reorganization, in hormone signaling pathways or encoding cytochrome were also differentially expressed. In addition, novel transcripts were identified, providing another basis for further characterization of plant defense-related genes. Overall, this study gives a first insight of the peach defense mechanisms during the very early stages of infection with a bacterial disease in the case of a compatible interaction.

Phylogenomics of the benzoxazinoid biosynthetic pathway of Poaceae: gene duplications and origin of the Bx cluster

Background

The benzoxazinoids 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA) and 2,4-dihydroxy-7- methoxy-1,4-benzoxazin-3-one (DIMBOA), are key defense compounds present in major agricultural crops such as maize and wheat. Their biosynthesis involves nine enzymes thought to form a linear pathway leading to the storage of DI(M)BOA as glucoside conjugates. Seven of the genes (Bx1-Bx6 and Bx8) form a cluster at the tip of the short arm of maize chromosome 4 that includes four P450 genes (Bx2-5) belonging to the same CYP71C subfamily. The origin of this cluster is unknown.

Results

We show that the pathway appeared following several duplications of the TSA gene (α-subunit of tryptophan synthase) and of a Bx2-like ancestral CYP71C gene and the recruitment of Bx8 before the radiation of Poaceae. The origins of Bx6 and Bx7 remain unclear. We demonstrate that the Bx2-like CYP71C ancestor was not committed to the benzoxazinoid pathway and that after duplications the Bx2-Bx5 genes were under positive selection on a few sites and underwent functional divergence, leading to the current specific biochemical properties of the enzymes. The absence of synteny between available Poaceae genomes involving the Bx gene regions is in contrast with the conserved synteny in the TSA gene region.

Conclusions

These results demonstrate that rearrangements following duplications of an IGL/TSA gene and of a CYP71C gene probably resulted in the clustering of the new copies (Bx1 and Bx2) at the tip of a chromosome in an ancestor of grasses. Clustering favored cosegregation and tip chromosomal location favored gene rearrangements that allowed the further recruitment of genes to the pathway. These events, a founding event and elongation events, may have been the key to the subsequent evolution of the benzoxazinoid biosynthetic cluster.

Transcript profiling of the phytotoxic response of wheat to the Fusarium mycotoxin deoxynivalenol

Deoxynivalenol (DON) is a trichothecene mycotoxin commonly produced by Fusarium graminearum and F. culmorum during infection of cereal plants, such as wheat and barley. This toxin is a fungal virulence factor that facilitates the development of Fusarium head blight (FHB) disease. Wheat cultivar (cv.) Remus is susceptible to DON; the toxin causes premature bleaching of spikelets and inhibits root growth. This study used custom-made wheat cDNA arrays to analyse the effect of DON on the transcriptome of heads of the toxin-sensitive wheat cv. Remus at both 4 and 24 h post-toxin treatment. DON-induced transcripts encoded an array of proteins collectively associated with a range of cellular functions, such as metabolite transformation and detoxification, the ubiquitin-proteasome proteolytic pathway, jasmonate biosynthesis and signalling, carbohydrate metabolism, and phenylpropanoid biosynthesis. This study is the first to demonstrate that the fungal virulence factor DON modulates jasmonate biosynthesis and signalling. It also highlights the fact that the toxin-mediated accumulation of transcripts associated with metabolite transformation and detoxification, proteolysis and phenylpropanoid accumulation is not unique to DON-resistant wheat genotypes. Therefore, the respective encoded proteins are likely part of the general wheat defence against DON. Comparative analysis of the results of this and other studies suggests that it is likely to be the rapidity and magnitude rather than the components of the response that are critical in determining resistance to DON and thus the spread of FHB disease in wheat heads.

The extreme dwarf phenotype of the GA-sensitive mutant of sunflower, dwarf2, is generated by a deletion in the ent-kaurenoic acid oxidase1 (HaKAO1) gene sequence

A dwarf mutant, dw arf 2 (dw2), was isolated from sunflower (Helianthus annuus). The most obvious alterations of dw2 plants were the lack of stem growth, reduced size of leaves, petioles and flower organs, retarded flower development. Pollen and ovules were produced but the filaments failed to extrude the anthers from the corolla. The dw2 phenotype was mainly because of reduced cell size. In dw2 leaves, the dark-green color was not so much due to higher pigment content, but was correlated with a changed leaf morphology. The mutant responded to the application of bioactive gibberellins (GAs). The levels of ent-7α-hydroxykaurenoic acid, GA(19), GA(20) and GA(1) in dw2 seedlings were severely decreased relative to those in its wild type (WT). ent-Kaurenoic acid was actively converted to ent-7α-hydroxykaurenoic acid in WT plants but quite poorly in dw2 plants. All together these data suggested that the dw2 mutation severely reduced the flux through the biosynthetic pathway leading to active GAs by hampering the conversion of ent-kaurenoic acid to GA(12). Two ent-kaurenoic acid oxidase (KAO) genes were identified. HaKAO1 was expressed everywhere in sunflower organs, while HaKAO2 was mainly expressed in roots. We demonstrated that a DNA deletion in HaKAO1 of dw2 generated aberrant mRNA-splicing, causing a premature stop codon in the amino acid sequence. In dw2 calli, Agrobacterium-mediated transfer of WT HaKAO1 cDNA restored the WT endogenous levels of GAs. In segregating BC(1) progeny, the deletion co-segregated with the dwarf phenotype. The deletion was generated near to a breakpoint of a more complex chromosome rearrangement.

Triterpenoid biosynthesis and engineering in plants

Triterpenoid saponins are a diverse group of natural products in plants and are considered defensive compounds against pathogenic microbes and herbivores. Because of their various beneficial properties for humans, saponins are used in wide-ranging applications in addition to medicinally. Saponin biosynthesis involves three key enzymes: oxidosqualene cyclases, which construct the basic triterpenoid skeletons; cytochrome P450 monooxygenases, which mediate oxidations; and uridine diphosphate-dependent glycosyltransferases, which catalyze glycosylations. The discovery of genes committed to saponin biosynthesis is important for the stable supply and biotechnological application of these compounds. Here, we review the identified genes involved in triterpenoid biosynthesis, summarize the recent advances in the biotechnological production of useful plant terpenoids, and discuss the bioengineering of plant triterpenoids.

The phenylpropanoid pathway in Arabidopsis

The phenylpropanoid pathway serves as a rich source of metabolites in plants, being required for the biosynthesis of lignin, and serving as a starting point for the production of many other important compounds, such as the flavonoids, coumarins, and lignans. In spite of the fact that the phenylpropanoids and their derivatives are sometimes classified as secondary metabolites, their relevance to plant survival has been made clear via the study of Arabidopsis and other plant species. As a model system, Arabidopsis has helped to elucidate many details of the phenylpropanoid pathway, its enzymes and intermediates, and the interconnectedness of the pathway with plant metabolism as a whole. These advances in our understanding have been made possible in large part by the relative ease with which mutations can be generated, identified, and studied in Arabidopsis. Herein, we provide an overview of the research progress that has been made in recent years, emphasizing both the genes (and gene families) associated with the phenylpropanoid pathway in Arabidopsis, and the end products that have contributed to the identification of many mutants deficient in the phenylpropanoid metabolism: the sinapate esters.

Arabidopsis CYP72C1 is an atypical cytochrome P450 that inactivates brassinosteroids

Cytochrome P450 monooxygenases (P450s) are a diverse family of proteins that have specialized roles in secondary metabolism and in normal cell development. Two P450s in particular, CYP734A1 and CYP72C1, have been identified as brassinosteroid-inactivating enzymes important for steroid-mediated signal transduction in Arabidopsis thaliana. Genetic analyses have demonstrated that these P450s modulate growth throughout plant development. While members of the CYP734A subfamily inactivate brassinosteroids through C-26 hydroxylation, the biochemical activity of CYP72C1 is unknown. Because CYP734A1 and CYP72C1 in Arabidopsis diverge more than brassinosteroid inactivating P450s in other plants, this study examines the structure and biochemistry of each enzyme. Three-dimensional models were generated to examine the substrate binding site structures and determine how they might affect the function of each P450. These models have indicated that the active site of CYP72C1 does not contain several conserved amino acids typically needed for substrate hydroxylation. Heterologous expression of these P450s followed by substrate binding analyses have indicated that CYP734A1 binds active brassinosteroids, brassinolide and castasterone, as well as their upstream precursors whereas CYP72C1 binds precursors more effectively. Seedling growth assays have demonstrated that the genetic state of CYP734A1, but not CYP72C1, affected responsiveness to high levels of exogenous brassinolide supporting our observations that CYP72C1 acts on brassinolide precursors. Although there may be some overlap in their physiological function, the distinct biochemical functions of these proteins in Arabidopsis has significant potential to fine-tune the levels of different brassinosteroid hormones throughout plant growth and development.

Homologues of the Arabidopsis thaliana SHI/STY/LRP1 genes control auxin biosynthesis and affect growth and development in the moss Physcomitrella patens

The plant hormone auxin plays fundamental roles in vascular plants. Although exogenous auxin also stimulates developmental transitions and growth in non-vascular plants, the effects of manipulating endogenous auxin levels have thus far not been reported. Here, we have altered the levels and sites of auxin production and accumulation in the moss Physcomitrella patens by changing the expression level of homologues of the Arabidopsis SHI/STY family proteins, which are positive regulators of auxin biosynthesis genes. Constitutive expression of PpSHI1 resulted in elevated auxin levels, increased and ectopic expression of the auxin response reporter GmGH3pro:GUS, and in an increased caulonema/chloronema ratio, an effect also induced by exogenous auxin application. In addition, we observed premature ageing and necrosis in cells ectopically expressing PpSHI1. Knockout of either of the two PpSHI genes resulted in reduced auxin levels and auxin biosynthesis rates in leafy shoots, reduced internode elongation, delayed ageing, a decreased caulonema/chloronema ratio and an increased number of axillary hairs, which constitute potential auxin biosynthesis sites. Some of the identified auxin functions appear to be analogous in vascular and non-vascular plants. Furthermore, the spatiotemporal expression of the PpSHI genes and GmGH3pro:GUS strongly overlap, suggesting that local auxin biosynthesis is important for the regulation of auxin peak formation in non-vascular plants.

Genomic and coexpression analyses predict multiple genes involved in triterpene saponin biosynthesis in Medicago truncatula

Saponins, an important group of bioactive plant natural products, are glycosides of triterpenoid or steroidal aglycones (sapogenins). Saponins possess many biological activities, including conferring potential health benefits for humans. However, most of the steps specific for the biosynthesis of triterpene saponins remain uncharacterized at the molecular level. Here, we use comprehensive gene expression clustering analysis to identify candidate genes involved in the elaboration, hydroxylation, and glycosylation of the triterpene skeleton in the model legume Medicago truncatula. Four candidate uridine diphosphate glycosyltransferases were expressed in Escherichia coli, one of which (UGT73F3) showed specificity for multiple sapogenins and was confirmed to glucosylate hederagenin at the C28 position. Genetic loss-of-function studies in M. truncatula confirmed the in vivo function of UGT73F3 in saponin biosynthesis. This report provides a basis for future studies to define genetically the roles of multiple cytochromes P450 and glycosyltransferases in triterpene saponin biosynthesis in Medicago.

Identification and characterisation of CYP75A31, a new flavonoid 3'5'-hydroxylase, isolated from Solanum lycopersicum

BACKGROUND

Understanding the regulation of the flavonoid pathway is important for maximising the nutritional value of crop plants and possibly enhancing their resistance towards pathogens. The flavonoid 3'5'-hydroxylase (F3'5'H) enzyme functions at an important branch point between flavonol and anthocyanin synthesis, as is evident from studies in petunia (Petunia hybrida), and potato (Solanum tuberosum). The present work involves the identification and characterisation of a F3'5'H gene from tomato (Solanum lycopersicum), and the examination of its putative role in flavonoid metabolism.

RESULTS

The cloned and sequenced tomato F3'5'H gene was named CYP75A31. The gene was inserted into the pYeDP60 expression vector and the corresponding protein produced in yeast for functional characterisation. Several putative substrates for F3'5'H were tested in vitro using enzyme assays on microsome preparations. The results showed that two hydroxylation steps occurred. Expression of the CYP75A31 gene was also tested in vivo, in various parts of the vegetative tomato plant, along with other key genes of the flavonoid pathway using real-time PCR. A clear response to nitrogen depletion was shown for CYP75A31 and all other genes tested. The content of rutin and kaempferol-3-rutinoside was found to increase as a response to nitrogen depletion in most parts of the plant, however the growth conditions used in this study did not lead to accumulation of anthocyanins.

CONCLUSIONS

CYP75A31 (NCBI accession number GQ904194), encodes a flavonoid 3'5'-hydroxylase, which accepts flavones, flavanones, dihydroflavonols and flavonols as substrates. The expression of the CYP75A31 gene was found to increase in response to nitrogen deprivation, in accordance with other genes in the phenylpropanoid pathway, as expected for a gene involved in flavonoid metabolism.