A Single Nucleotide Mutation of the IspE Gene Participating in the MEP Pathway for Isoprenoid Biosynthesis Causes a Green-Revertible Yellow Leaf Phenotype in Rice

Mitochondrial ATP Synthase beta-Subunit Affects Plastid Retrograde Signaling in Arabidopsis

Plastid retrograde signaling plays a key role in coordinating the expression of plastid genes and photosynthesis-associated nuclear genes (PhANGs). Although plastid retrograde signaling can be substantially compromised by mitochondrial dysfunction, it is not yet clear whether specific mitochondrial factors are required to regulate plastid retrograde signaling. Here, we show that mitochondrial ATP synthase beta-subunit mutants with decreased ATP synthase activity are impaired in plastid retrograde signaling in Arabidopsis thaliana. Transcriptome analysis revealed that the expression levels of PhANGs were significantly higher in the mutants affected in the AT5G08670 gene encoding the mitochondrial ATP synthase beta-subunit, compared to wild-type (WT) seedlings when treated with lincomycin (LIN) or norflurazon (NF). Further studies indicated that the expression of nuclear genes involved in chloroplast and mitochondrial retrograde signaling was affected in the AT5G08670 mutant seedlings treated with LIN. These changes might be linked to the modulation of some transcription factors (TFs), such as LHY (Late Elongated Hypocotyl), PIF (Phytochrome-Interacting Factors), MYB, WRKY, and AP2/ERF (Ethylene Responsive Factors). These findings suggest that the activity of mitochondrial ATP synthase significantly influences plastid retrograde signaling.

Multi-omics analyses provide insights into the evolutionary history and the synthesis of medicinal components of the Chinese wingnut

Chinese wingnut (Pterocarya stenoptera) is a medicinally and economically important tree species within the family Juglandaceae. However, the lack of high-quality reference genome has hindered its in-depth research. In this study, we successfully assembled its chromosome-level genome and performed multi-omics analyses to address its evolutionary history and synthesis of medicinal components. A thorough examination of genomes has uncovered a significant expansion in the Lateral Organ Boundaries Domain gene family among the winged group in Juglandaceae. This notable increase may be attributed to their frequent exposure to flood-prone environments. After further differentiation between Chinese wingnut and Cyclocarya paliurus, significant positive selection occurred on the genes of NADH dehydrogenase related to mitochondrial aerobic respiration in Chinese wingnut, enhancing its ability to cope with waterlogging stress. Comparative genomic analysis revealed Chinese wingnut evolved more unique genes related to arginine synthesis, potentially endowing it with a higher capacity to purify nutrient-rich water bodies. Expansion of terpene synthase families enables the production of increased quantities of terpenoid volatiles, potentially serving as an evolved defense mechanism against herbivorous insects. Through combined transcriptomic and metabolomic analysis, we identified the candidate genes involved in the synthesis of terpenoid volatiles. Our study offers essential genetic resources for Chinese wingnut, unveiling its evolutionary history and identifying key genes linked to the production of terpenoid volatiles.

YGL3 Encoding an IPP and DMAPP Synthase Interacts with OsPIL11 to Regulate Chloroplast Development in Rice

As the source of isoprenoid precursors, the plastidial methylerythritol phosphate (MEP) pathway plays an essential role in plant development. Here, we report a novel rice (Oryza sativa L.) mutant ygl3 (yellow-green leaf3) that exhibits yellow-green leaves and lower photosynthetic efficiency compared to the wild type due to abnormal chloroplast ultrastructure and reduced chlorophyll content. Map-based cloning showed that YGL3, one of the major genes involved in the MEP pathway, encodes 4-hydroxy-3-methylbut-2-enyl diphosphate reductase, which is localized in the thylakoid membrane. A single base substitution in ygl3 plants resulted in lower 4-hydroxy-3-methylbut-2-enyl diphosphate reductase activity and lower contents of isopentenyl diphosphate (IPP) compared to the wild type. The transcript levels of genes involved in the syntheses of chlorophyll and thylakoid membrane proteins were significantly reduced in the ygl3 mutant compared to the wild type. The phytochrome interacting factor-like gene OsPIL11 regulated chlorophyll synthesis during the de-etiolation process by directly binding to the promoter of YGL3 to activate its expression. The findings provides a theoretical basis for understanding the molecular mechanisms by which the MEP pathway regulate chloroplast development in rice.

Yellow-Green Leaf 19 Encoding a Specific and Conservative Protein for Photosynthetic Organisms Affects Tetrapyrrole Biosynthesis, Photosynthesis, and Reactive Oxygen Species Metabolism in Rice

Chlorophyll is the main photosynthetic pigment and is crucial for plant photosynthesis. Leaf color mutants are widely used to identify genes involved in the synthesis or metabolism of chlorophyll. In this study, a spontaneous mutant, yellow-green leaf 19 (ygl19), was isolated from rice (Oryza sativa). This ygl19 mutant showed yellow-green leaves and decreased chlorophyll level and net photosynthetic rate. Brown necrotic spots appeared on the surface of ygl19 leaves at the tillering stage. And the agronomic traits of the ygl19 mutant, including the plant height, tiller number per plant, and total number of grains per plant, were significantly reduced. Map-based cloning revealed that the candidate YGL19 gene was LOC_Os03g21370. Complementation of the ygl19 mutant with the wild-type CDS of LOC_Os03g21370 led to the restoration of the mutant to the normal phenotype. Evolutionary analysis revealed that YGL19 protein and its homologues were unique for photoautotrophs, containing a conserved Ycf54 functional domain. A conserved amino acid substitution from proline to serine on the Ycf54 domain led to the ygl19 mutation. Sequence analysis of the YGL19 gene in 4726 rice accessions found that the YGL19 gene was conserved in natural rice variants with no resulting amino acid variation. The YGL19 gene was mainly expressed in green tissues, especially in leaf organs. And the YGL19 protein was localized in the chloroplast for function. Gene expression analysis via qRT-PCR showed that the expression levels of tetrapyrrole synthesis-related genes and photosynthesis-related genes were regulated in the ygl19 mutant. Reactive oxygen species (ROS) such as superoxide anions and hydrogen peroxide accumulated in spotted leaves of the ygl19 mutant at the tillering stage, accompanied by the regulation of ROS scavenging enzyme-encoding genes and ROS-responsive defense signaling genes. This study demonstrates that a novel yellow-green leaf gene YGL19 affects tetrapyrrole biosynthesis, photosynthesis, and ROS metabolism in rice.

Identification and characterization of CsSRP43, a major gene controlling leaf yellowing in cucumber

Mutants are crucial to extending our understanding of genes and their functions in higher plants. In this study a spontaneous cucumber mutant, yf, showed yellow color leaves, had significant decreases in related physiological indexes of photosynthesis characteristics, and had more abnormal chloroplasts and thylakoids. Inheritance analysis indicated that the yellow color of the leaf was controlled by a recessive nuclear locus, yf. A candidate gene, CsSRP43, encoding a chloroplast signal recognition particle 43 protein, was identified through map-based cloning and whole-genome sequence analysis. Alignment of the CsSRP43 gene homologs between both parental lines revealed a 7-kb deletion mutation including the promoter region and the coding sequence in the yf mutant. In order to determine if the CsSRP43 gene was involved in the formation of leaf color, the CRISPR/Cas9-mediate system was used to modify CsSRP43 in the 9930 background; two independent transgenic lines, srp43-1 and srp43-2, were generated, and they showed yellow leaves with abnormal chloroplasts and thylakoids. Transcriptomic analysis revealed that differentially expressed genes associated with the photosynthesis-related pathway were highly enriched between srp43-1 and wild type, most of which were significantly downregulated in line srp43-1. Furthermore, yeast two-hybrid and biomolecular fluorescence complementation assays were used to confirm that CsSRP43 directly interacted with LHCP and cpSRP54 proteins. A model was established to explain the molecular mechanisms by which CsSRP43 participates in the leaf color and photosynthesis pathway, and it provides a valuable basis for understanding the molecular and genetic mechanisms of leaf color in cucumber.

Exon skipping in IspE Gene is associated with abnormal chloroplast development in rice albino leaf 4 mutant

The formation of leaf color largely depends on the components of pigment accumulation in plastids, which are involved in chloroplast development and division. Here, we isolated and characterized the rice albino leaf 4 (al4) mutant, which exhibited an albino phenotype and eventually died at the three-leaf stage. The chloroplasts in al4 mutant were severely damaged and unable to form intact thylakoid structure. Further analysis revealed that the candidate gene encodes 4-diphosphocytidyl-2-C-methyl-D-erythritol kinase (IspE), which participates in the methylerythritol phosphate (MEP) pathway of isoprenoid biosynthesis. We further demonstrated that the mutation at the exon-intron junction site cause alternative splicing factors fail to distinguish the origin of the GT-AG intron, leading to exon skipping and producing a truncated OsIspE in the al4 mutant. Notably, disruption of OsIspE led to the reduced expression of chloroplast-associated genes, including chloroplast biosynthetic and translation related genes and photosynthetic associated nuclear genes (PhANGs). In summary, these findings reveal that OsIspE plays a crucial role in chloroplast biogenesis and provides novel insights into the function of CMK during chloroplast development in rice.

Cytological, genetic and transcriptomic characterization of a cucumber albino mutant

Photosynthesis, a fundamental process for plant growth and development, is dependent on chloroplast formation and chlorophyll synthesis. Severe disruption of chloroplast structure results in albinism of higher plants. In the present study, we report a cucumber albino alc mutant that presented white cotyledons under normal light conditions and was unable to produce first true leaf. Meanwhile, alc mutant could grow creamy green cotyledons under dim light conditions but died after exposure to normal light irradiation. No chlorophyll and carotenoid were detected in the alc mutant grown under normal light conditions. Using transmission electron microscopy, impaired chloroplasts were observed in this mutant. The genetic analysis indicated that the albino phenotype was recessively controlled by a single locus. Comparative transcriptomic analysis between the alc mutant and wild type revealed that genes involved in chlorophyll metabolism and the methylerythritol 4-phosphate pathway were affected in the alc mutant. In addition, three genes involved in chloroplast development, including two FtsH genes and one PPR gene, were found to have negligible expression in this mutant. The quality of RNA sequencing results was further confirmed by real-time quantitative PCR analysis. We also examined 12 homologous genes from alc mutant in other plant species, but no genetic variation in the coding sequences of these genes was found between alc mutant and wild type. Taken together, we characterized a cucumber albino mutant with albinism phenotype caused by chloroplast development deficiency and this mutant can pave way for future studies on plastid development.

PGD: a machine learning-based photosynthetic-related gene detection approach

Background

The primary determinant of crop yield is photosynthetic capacity, which is under the control of photosynthesis-related genes. Therefore, the mining of genes involved in photosynthesis is important for the study of photosynthesis. MapMan Mercator 4 is a powerful annotation tool for assigning genes into proper functional categories; however, in maize, the functions of approximately 22.15% (9520) of genes remain unclear and are labeled “not assigned”, which may include photosynthesis-related genes that have not yet been identified. The fast-increasing usage of the machine learning approach in solving biological problems provides us with a new chance to identify novel photosynthetic genes from functional “not assigned” genes in maize.

Results

In this study, we proved the ensemble learning model using a voting eliminates the preferences of single machine learning models. Based on this evaluation, we implemented an ensemble based ML(Machine Learning) methods using a majority voting scheme and observed that including RNA-seq data from multiple photosynthetic mutants rather than only a single mutant could increase prediction accuracy. And we call this approach “A Machine Learning-based Photosynthetic-related Gene Detection approach (PGD)”. Finally, we predicted 716 photosynthesis-related genes from the “not assigned” category of maize MapMan annotation. The protein localization prediction (TargetP) and expression trends of these genes from maize leaf sections indicated that the prediction was reliable and robust. And we put this approach online base on google colab.

Conclusions

This study reveals a new approach for mining novel genes related to a specific functional category and provides candidate genes for researchers to experimentally define their biological functions.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12859-022-04722-x.

The Genetic Components of a Natural Color Palette: A Comprehensive List of Carotenoid Pathway Mutations in Plants

Carotenoids comprise the most widely distributed natural pigments. In plants, they play indispensable roles in photosynthesis, furnish colors to flowers and fruit and serve as precursor molecules for the synthesis of apocarotenoids, including aroma and scent, phytohormones and other signaling molecules. Dietary carotenoids are vital to human health as a source of provitamin A and antioxidants. Hence, the enormous interest in carotenoids of crop plants. Over the past three decades, the carotenoid biosynthesis pathway has been mainly deciphered due to the characterization of natural and induced mutations that impair this process. Over the year, numerous mutations have been studied in dozens of plant species. Their phenotypes have significantly expanded our understanding of the biochemical and molecular processes underlying carotenoid accumulation in crops. Several of them were employed in the breeding of crops with higher nutritional value. This compendium of all known random and targeted mutants available in the carotenoid metabolic pathway in plants provides a valuable resource for future research on carotenoid biosynthesis in plant species.

Beyond the darkness: recent lessons from etiolation and de-etiolation studies

The state of etiolation is generally defined by the presence of non-green plastids (etioplasts) in plant tissues that would normally contain chloroplasts. In the commonly used dark-grown seedling system, etiolation is coupled with a type of growth called skotomorphogenesis. Upon illumination, de-etiolation occurs, marked by the transition from etioplast to chloroplast, and, at the seedling level, a switch to photomorphogenic growth. Etiolation and de-etiolation systems are therefore important for understanding both the acquisition of photosynthetic capacity during chloroplast biogenesis and plant responses to light-the most relevant signal in the life and growth of the organism. In this review, we discuss recent discoveries (within the past 2-3 years) in the field of etiolation and de-etiolation, with a particular focus on post-transcriptional processes and ultrastructural changes. We further discuss ambiguities in definitions of the term 'etiolation', and benefits and biases of common etiolation/de-etiolation systems. Finally, we raise several open questions and future research possibilities.

Pathways for Carotenoid Biosynthesis, Degradation, and Storage

Carotenoids are isoprenoid compounds synthesized de novo in all photosynthetic organisms as well as in some nonphotosynthetic bacteria and fungi. In plants, carotenoids are essential for light harvesting and photoprotection. They contribute to the vivid color found in many plant organs. The cleavage of carotenoids produces small molecules (apocarotenoids) that serve as aroma compounds, as well as phytohormones and signals to affect plant growth and development. Since carotenoids provide valuable nutrition and health benefits for humans, understanding of carotenoid biosynthesis, catabolism and storage is important for biofortification of crops with improved nutritional quality. This chapter primarily introduces our current knowledge about carotenoid biosynthesis and degradation pathways as well as carotenoid storage in plants.

A phosphofructokinase B-type carbohydrate kinase family protein, PFKB1, is essential for chloroplast development at early seedling stage in rice

Among the phosphofructokinase B-type carbohydrate kinase (PCK) family proteins, only few proteins, like the FRUCTOKINASE-LIKE 1 and 2, have been functionally characterized in regulation of chloroplast development. Here, we report the involvement of a PCK protein PFKB1 in chloroplast development by identification of a new rice mutant, revertible early yellowing Kitaake 2 [rey(k2)]. The mutant rey(k2) shows yellow leaf phenotype, reduced photosynthetic pigments, and retarded chloroplast development during early stages of seedlings, but gradually recovered at later stages. The phenotype of rey(k2) is resulted from the disruption of the PFKB1 protein. The Pfkb1 gene is ubiquitously expressed, and its protein is mainly targeted to the chloroplast and, in some cells, to the nucleus. In addition, the PFKB1 protein possesses phosphofructokinase activity in vitro. The rey(k2) mutant affects RNA levels of chloroplast-associated genes. In particular, the nuclear-encoded RNA polymerase (NEP)-dependent genes are expressed at a sustained high level in rey(k2) even after turning green, indicating that PFKB1 is essential for suppressing the expression of NEP-dependent genes. Taken together, our study suggests that PFKB1 functions as a novel regulator indispensable for early chloroplast development, at least partly by regulating chloroplast-associated genes.

Antibacterial activity of 2-amino-4-hydroxypyrimidine-5-carboxylates and binding to Burkholderia pseudomallei 2-C-methyl-d-erythritol-2,4-cyclodiphosphate synthase

Enzymes in the methylerythritol phosphate pathway make attractive targets for antibacterial activity due to their importance in isoprenoid biosynthesis and the absence of the pathway in mammals. The fifth enzyme in the pathway, 2-C-methyl-d-erythritol-2,4-cyclodiphosphate synthase (IspF), contains a catalytically important zinc ion in the active site. A series of de novo designed compounds containing a zinc binding group was synthesized and evaluated for antibacterial activity and interaction with IspF from Burkholderia pseudomallei, the causative agent of Whitmore's disease. The series demonstrated antibacterial activity as well as protein stabilization in fluorescence-based thermal shift assays. Finally, the binding of one compound to Burkholderia pseudomallei IspF was evaluated through group epitope mapping by saturation transfer difference NMR.

GRA78 encoding a putative S-sulfocysteine synthase is involved in chloroplast development at the early seedling stage of rice

Cysteine functions not only as an amino acid in proteins but also as a precursor for a large number of essential biomolecules. Cysteine is synthesized via the incorporation of sulfide to O-acetylserine under the catalysis of O-acetylserine(thiol)lyase (OASTL). In dicotyledonous Arabidopsis, nine OASTL genes have been reported. However, in their null mutants, only the mutant of CS26 encoding S-sulfocysteine synthase showed the visible phenotypic changes, displaying significantly small plants and pale-green leaves under long-day condition but not short-day condition. Up to now, no OASTL gene or mutant has been identified in monocotyledon. In this study, we isolated a green-revertible albino mutant gra78 in rice (Oryza sativa). Its albino phenotype at the early seedling stage was sensitive to temperature but independent of photoperiod. Map-based cloning revealed that candidate gene LOC_Os01g59920 of GRA78 encodes a putative S-sulfocysteine synthase showing significant similarity with Arabidopsis CS26. Complementation experiment confirmed that mutation in LOC_Os01g59920 accounted for the mutant phenotype of gra78. GRA78 is constitutively expressed in all tissues and its encoded protein is targeted to the chloroplast. In addition, qRT-PCR suggested that expression levels of four OASTL homolog genes and five photosynthetic genes were remarkably down-regulated.