Comprehensive transcriptome analysis discovers novel candidate genes related to leaf color in a Lagerstroemia indica yellow leaf mutant

Integrating Physiology, Cytology, and Transcriptome to Reveal the Leaf Variegation Mechanism in Phalaenopsis Chia E Yenlin Variegata Leaves

Phalaenopsis orchids, with their unique appearance and extended flowering period, are among the most commercially valuable Orchidaceae worldwide. Particularly, the variegation in leaf color of Phalaenopsis significantly enhances the ornamental and economic value and knowledge of the molecular mechanism of leaf-color variegation in Phalaenopsis is lacking. In this study, an integrative analysis of the physiology, cytology, and transcriptome profiles was performed on Phalaenopsis Chia E Yenlin Variegata leaves between the green region (GR) and yellow region (YR) within the same leaf. The total chlorophyll and carotenoid contents in the YR exhibited a marked decrease of 72.18% and 90.21%, respectively, relative to the GR. Examination of the ultrastructure showed that the chloroplasts of the YR were fewer and smaller and exhibited indistinct stromal lamellae, ruptured thylakoids, and irregularly arranged plastoglobuli. The transcriptome sequencing between the GR and YR led to a total of 3793 differentially expressed genes, consisting of 1769 upregulated genes and 2024 downregulated genes. Among these, the chlorophyll-biosynthesis-related genes HEMA, CHLH, CRD, and CAO showed downregulation, while the chlorophyll-degradation-related gene SGR had an upregulated expression in the YR. Plant-hormone-related genes and transcription factors MYBs (37), NACs (21), ERFs (20), bHLH (13), and GLK (2), with a significant difference, were also analyzed. Furthermore, qRT-PCR experiments validated the above results. The present work establishes a genetic foundation for future studies of leaf-pigment mutations and may help to improve the economic and breeding values of Phalaenopsis.

Genome assembly and resequencing analyses provide new insights into the evolution, domestication and ornamental traits of crape myrtle

Crape myrtle (Lagerstroemia indica) is a globally used ornamental woody plant and is the representative species of Lagerstroemia. However, studies on the evolution and genomic breeding of L. indica have been hindered by the lack of a reference genome. Here we assembled the first high-quality genome of L. indica using PacBio combined with Hi-C scaffolding to anchor the 329.14-Mb genome assembly into 24 pseudochromosomes. We detected a previously undescribed independent whole-genome triplication event occurring 35.5 million years ago in L. indica following its divergence from Punica granatum. After resequencing 73 accessions of Lagerstroemia, the main parents of modern crape myrtle cultivars were found to be L. indica and L. fauriei. During the process of domestication, genetic diversity tended to decrease in many plants, but this was not observed in L. indica. We constructed a high-density genetic linkage map with an average map distance of 0.33 cM. Furthermore, we integrated the results of quantitative trait locus (QTL) using genetic mapping and bulk segregant analysis (BSA), revealing that the major-effect interval controlling internode length (IL) is located on chr1, which contains CDL15, CRG98, and GID1b1 associated with the phytohormone pathways. Analysis of gene expression of the red, purple, and white flower-colour flavonoid pathways revealed that differential expression of multiple genes determined the flower colour of L. indica, with white flowers having the lowest gene expression. In addition, BSA of purple- and green-leaved individuals of populations of L. indica was performed, and the leaf colour loci were mapped to chr12 and chr17. Within these intervals, we identified MYB35, NCED, and KAS1. Our genome assembly provided a foundation for investigating the evolution, population structure, and differentiation of Myrtaceae species and accelerating the molecular breeding of L. indica.

Physiological, transcriptome and co-expression network analysis of chlorophyll-deficient mutants in flue-cured tobacco

BACKGROUND

Photosynthetic pigments in higher plants, including chlorophyll (Chl) and carotenoids, are crucial for photosynthesis and photoprotection. Chl-deficient tobacco seedlings generally have a lower photosynthesis rate and higher nitrate-nitrogen (NO₃-N) content, which causes a profound influence on tobacco yield and quality. In this study, a stable albino leaf mutant (Al) and slight-green leaf mutant (SG) obtained from the common flue-cured tobacco (Nicotiana tabacum L.) cultivar 'Zhongyan 100' (ZY100) by mutagenesis with ethyl methanesulfonate (EMS) were used as materials. The differences between the Chl-deficient mutants and the wild-type (WT) were analyzed in terms of biomass, photosynthetic fluorescence parameters, and carbon- and nitrogen-related physiological parameters. RNA sequencing (RNA-seq) and weighted gene co-expression network analysis (WGCNA) were used to explore the key pathways and candidate genes regulating differentiated chlorophyll and nitrate content.

RESULTS

The results showed that, when compared to the WT, the Chl content and biomass of mutant plants were considerably lower while the NO₃-N content was substantially elevated. The net photosynthetic rate, photosynthetic fluorescence parameters, carbohydrate, soluble protein, and carbon- and nitrogen-related enzyme activities all decreased in leaves of mutants and the development of chloroplasts was abnormal. Applying more nitrogen improved the growth and development of mutants, whereas NO₃-N content distinctively increased compared with that of the WT. Through transcriptome sequencing, the downregulated genes in mutants were enriched in plant hormone signal transduction and nitrogen metabolism, which are involved in pigment biosynthesis and the carbon fixation pathway. In addition, two hub genes and seven transcription factors identified from the blue module through WGCNA were likely to be key candidate factors involved in chlorophyll synthesis and nitrate accumulation.

CONCLUSION

Our results demonstrated that differences in chlorophyll and nitrate content were caused by the combined effects of chloroplast development, photosynthesis, as well as related biological activity. In addition, transcriptome results provide a bioinformatics resource for further functional identification of key pathways and genes responsible for differences in chlorophyll and nitrate content in tobacco plants.

The oxidative damage of the Lagerstroemia indica chlorosis mutant gl1 involves in ferroptosis

Photooxidation is the major physiological performance of the Lagerstroemia indica chlorosis mutant gl1 under field conditions. The mechanisms of the progressive symptoms of oxidative damage from the lower older leaves to the upper mature leaves are complicated and still unclear. The aim of this work was to investigate the physiological mechanisms of oxidative stress from the perspective of the photosynthetic metabolites. The phytosynthetic metabolites of gl1 mutant changed significantly compared to wild type (WT) L. indica, such as by increasing phenolics, decreasing soluble sugar, protein and ascorbate, and redistributing antioxidant enzyme activities. The co-accumulation of phenolics and guaiacol-POD in gl1 mutant promote the removal of H₂O₂, as well the increase of phenoxyl radicals levels. Furthermore, the ion balance was significantly disturbed and Fe accumulated the most among these fluctuating nutrients in the leaves of gl1 mutant. The accumulated Fe was found neither in the chloroplasts nor in the cell wall of the leaves and became unshielded Fe, which favors the Fenton/Haber-Weiss reaction and stabilizes the phenoxyl radicals in metal complexation. The results suggested that the increase of phenolics and Fe accumulation were obviously involved in oxidative damage of gl1 mutant.

Identification and characterization of tsyl1, a thermosensitive chlorophyll-deficient mutant in rice (Oryza sativa)

Chloroplast development and chlorophyll biosynthesis are affected by temperature. However, the underlying molecular mechanism of this phenomenon remains elusive. Here, we isolated and characterized a thermosensitive yellow-green leaf mutant named tsyl1 (thermosensitive yellow leaf 1) from an ethylmethylsulfone (EMS)-mutagenized pool of rice. The mutant exhibits a yellow-green leaf phenotype and decreased leaf chlorophyll contents throughout development. At the mature stage of the tsyl1 mutant, the plant height, tiller number, number of spikelets per panicle and 1000 seed weight were decreased significantly compared to those of wild-type plants, but the seed setting rate and panicle length were not. The mutant phenotype was controlled by a single recessive nuclear gene on the short arm of rice chromosome 11. Map-based cloning of TSYL1, followed by a complementation experiment, showed a G base deletion at the coding region of LOC_Os11g05552, leading to the yellow-green phenotype. The TSYL1 gene encodes a signal recognition particle 54 kDa (SRP54) protein that is conserved in all organisms. The expression of tsyl1 was induced by high temperature. Furthermore, the expression of chlorophyll biosynthesis- and chloroplast development-related genes was influenced in tsyl1 at different temperatures. These results indicated that the TSYL1 gene plays a key role in chlorophyll biosynthesis and is affected by temperature at the transcriptional level.

Physiological analysis and transcriptome sequencing of a delayed-green leaf mutant 'Duojiao' of ornamental crabapple (Malus sp.)

Malus spectabilis 'Duojiao' is a spontaneous delayed-green leaf color mutant of M. spectabilis 'Riversii' and has chloroplasts with irregularly arranged vesicles and indistinct stromal lamellae. The yellow leaves of mutant have less chlorophyll (Chl), carotenoids, and flavonoids. Measurement of photosynthetic gas exchange indicated that the mutant has lower photosynthetic activity than 'Riversii' plants. Transcriptome sequencing with the Illumina platform was used to characterize differences in gene expression between the leaves of plants with yellow and green colors and elucidate the molecular mechanisms responsible for variation in leaf color in ornamental crabapple. In the comparison group of mutant yellow leaves and the maternal green leaves, 1848 differentially significant expressed genes (DEGs) were annotated by transcriptomic analysis. Many DEGs and transcription factors were identified related to chloroplast development, Chl synthesis and degradation, photosynthesis, carotenoid biosynthesis, flavonoid biosynthesis and other pathways related to plant leaf color formation. Among these, the Chl biosynthesis-related coproporphyrinogen gene, oxidative decarboxylase gene, and Chl a oxygenase gene were down-regulated, indicating that Chl biosynthesis was blocked. GLK1, which regulates chloroplast development, was down-regulated in yellow leaves. Parallel experiments showed that the content of the Chl synthesis precursors, protoporphyrinogen IX, chlorophyllide a, and chlorophyllide b and the activity of chlorophyllogen III oxidase and chlorophyllide a oxygenase in the yellow leaves of 'Duojiao' were lower than those in the green leaves of 'Riversii'. Thus, leaf color formation is greatly affected by Chl metabolism and chloroplast development. The reliability of the RNA-sequencing data was confirmed by quantitative real-time PCR analysis with 12 selected DEGs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-022-01248-7.

Dynamic transcriptome and network-based analysis of yellow leaf mutant Ginkgo biloba

BACKGROUND

Golden leaf in autumn is a prominent feature of deciduous tree species like Ginkgo biloba L., a landscape tree widely cultivated worldwide. However, little was known about the molecular mechanisms of leaf yellowing, especially its dynamic regulatory network. Here, we performed a suite of comparative physiological and dynamic transcriptional analyses on the golden-leaf cultivar and the wild type (WT) ginkgo to investigate the underlying mechanisms of leaf yellowing across different seasons.

RESULTS

In the present study, we used the natural bud mutant cultivar with yellow leaves "Wannianjin" (YL) as materials. Physiological analysis revealed that higher ratios of chlorophyll a to chlorophyll b and carotenoid to chlorophyll b caused the leaf yellowing of YL. On the other hand, dynamic transcriptome analyses showed that genes related to chlorophyll metabolism played key a role in leaf coloration. Genes encoding non-yellow coloring 1 (NYC1), NYC1-like (NOL), and chlorophyllase (CLH) involved in the degradation of chlorophyll were up-regulated in spring. At the summer stage, down-regulated HEMA encoding glutamyl-tRNA reductase functioned in chlorophyll biosynthesis, while CLH involved in chlorophyll degradation was up-regulated, causing a lower chlorophyll accumulation. In carotenoid metabolism, genes encoding zeaxanthin epoxidase (ZEP) and 9-cis-epoxy carotenoid dioxygenase (NCED) showed significantly different expression levels in the WT and YL. Moreover, the weighted gene co-expression network analysis (WGCNA) suggested that the most associated transcriptional factor, which belongs to the AP2/ERF-ERF family, was engaged in regulating pigment metabolism. Furthermore, quantitative experiments validated the above results.

CONCLUSIONS

By comparing the golden-leaf cultivar and the wide type of ginkgo across three seasons, this study not only confirm the vital role of chlorophyll in leaf coloration of YL but also provided new insights into the seasonal transcriptome landscape and co-expression network. Our novel results pinpoint candidate genes for further wet-bench experiments in tree species.

Comparative transcriptome analysis identified ChlH and POLGAMMA2 in regulating yellow-leaf coloration in Forsythia

Leaf color is one of the most important features for plants used for landscape and ornamental purposes. However, the regulatory mechanism of yellow leaf coloration still remains elusive in many plant species. To understand the complex genetic mechanism of yellow-leaf Forsythia, we first compared the pigment content and leaf anatomical structure of yellow-leaf and green-leaf accessions derived from a hybrid population. The physiological and cytological analyses demonstrated that yellow-leaf progenies were chlorophyll deficient with defected chloroplast structure. With comparative transcriptome analysis, we identified a number of candidate genes differentially expressed between yellow-leaf and green-leaf Forsythia plants. Among these genes, we further screened out two candidates, ChlH (magnesium chelatase Subunit H) and POLGAMMA2 (POLYMERASE GAMMA 2), with consistent relative-expression pattern between different colored plants. To verify the gene function, we performed virus-induced gene silencing assays and observed yellow-leaf phenotype with total chlorophyll content reduced by approximately 66 and 83% in ChlH-silenced and POLGAMMA2-silenced plants, respectively. We also observed defected chloroplast structure in both ChlH-silenced and POLGAMMA2-silenced Forsythia. Transient over-expression of ChlH and POLGAMMA2 led to increased chlorophyll content and restored thylakoid architecture in yellow-leaf Forsythia. With transcriptome sequencing, we detected a number of genes related to chlorophyll biosynthesis and chloroplast development that were responsive to the silencing of ChlH and POLGAMMA2. To summarize, ChlH and POLGAMMA2 are two key genes that possibly related to yellow-leaf coloration in Forsythia through modulating chlorophyll synthesis and chloroplast ultrastructure. Our study provided insights into the molecular aspects of yellow-leaf Forsythia and expanded the knowledge of foliage color regulation in woody ornamental plants.

Comparative physiology and transcriptome analysis reveals that chloroplast development influences silver-white leaf color formation in Hydrangea macrophylla var. maculata

BACKGROUND

Hydrangea macrophylla var. Maculata 'Yinbianxiuqiu' (YB) is an excellent plant species with beautiful flowers and leaves with silvery white edges. However, there are few reports on its leaf color characteristics and color formation mechanism.

RESULTS

The present study compared the phenotypic, physiological and transcriptomic differences between YB and a full-green leaf mutant (YM) obtained from YB. The results showed that YB and YM had similar genetic backgrounds, but photosynthesis was reduced in YB. The contents of pigments were significantly decreased at the edges of YB leaves compared to YM leaves. The ultrastructure of chloroplasts in the YB leaves was irregular. Transcriptome profiling identified 7,023 differentially expressed genes between YB and YM. The expression levels of genes involved in photosynthesis, chloroplast development and division were different between YB and YM. Quantitative real-time PCR showed that the expression trends were generally consistent with the transcriptome data.

CONCLUSIONS

Taken together, the formation of the silvery white leaf color of H. macrophylla var. maculata was primarily due to the abnormal development of chloroplasts. This study facilitates the molecular function analysis of key genes involved in chloroplast development and provides new insights into the molecular mechanisms involved in leaf coloration in H. macrophylla.

Analysis of Physiological and Transcriptomic Differences between a Premature Senescence Mutant (GSm) and Its Wild-Type in Common Wheat (Triticum aestivum L.)

Simple Summary

Early leaf senescence is an important agronomic trait that affects crop yield and quality. To understand the molecular mechanism of early leaf senescence, a wheat (Triticum aestivum L.) premature leaf senescence mutant (GSm) and its wild type were employed in this study. We compared the physiological characteristics and transcriptome of wheat leaves between the wild type (WT) and the mutant at two-time points. Physiological characteristics and differentially expressed gene (DEG) analysis revealed many genes and metabolic pathways that were closely related to senescence. These results will not only support further gene cloning and functional analysis of GSm, but also facilitate the study of leaf senescence in wheat.

Abstract

Premature leaf senescence has a profound influence on crop yield and quality. Here, a stable premature senescence mutant (GSm) was obtained from the common wheat (Triticum aestivum L.) cultivar Chang 6878 by mutagenesis with ethyl methanesulfonate. The differences between the GSm mutant and its wild-type (WT) were analyzed in terms of yield characteristics, photosynthetic fluorescence indices, and senescence-related physiological parameters. RNA sequencing was used to reveal gene expression differences between GSm and WT. The results showed that the yield of GSm was considerably lower than that of WT. The net photosynthetic rate, transpiration rate, maximum quantum yield, non-photochemical quenching coefficient, photosynthetic electron transport rate, soluble protein, peroxidase activity, and catalase activity all remarkably decreased in flag leaves of GSm, whereas malondialdehyde content distinctively increased compared with those of WT. The analysis of differentially expressed genes indicated blockade of chlorophyll and carotenoid biosynthesis, accelerated degradation of chlorophyll, and diminished photosynthetic capacity in mutant leaves; brassinolide might facilitate chlorophyll breakdown and consequently accelerate leaf senescence. NAC genes positively regulated the senescence process. Compared with NAC genes, expression of WRKY and MYB genes was induced earlier in the mutant possibly due to increased levels of reactive oxygen species and plant hormones (e.g., brassinolide, salicylic acid, and jasmonic acid), thereby accelerating leaf senescence. Furthermore, the antioxidant system played a role in minimizing oxidative damage in the mutant. These results provides novel insight into the molecular mechanisms of premature leaf senescence in crops.

Molecular and Photosynthetic Performance in the Yellow Leaf Mutant of Torreya grandis According to Transcriptome Sequencing, Chlorophyll a Fluorescence, and Modulated 820 nm Reflection

To study the photosynthetic energy mechanism and electron transfer in yellow leaves, transcriptomics combined with physiological approaches was used to explore the mechanism of the yellow leaf mutant Torreya grandis ‘Merrillii’. The results showed that chlorophyll content, the maximal photochemical efficiency of PSII (F_v/F_m), and the parameters related to the OJ phase of fluorescence (φ_Eo, φ_Ro) were all decreased significantly in mutant-type T. grandis leaves. The efficiency needed for an electron to be transferred from the reduced carriers between the two photosystems to the end acceptors of the PSI (δ_Ro) and the quantum yield of the energy dissipation (φ_Do) were higher in the leaves of mutant-type T. grandis compared to those in wild-type leaves. Analysis of the prompt fluorescence kinetics and modulated 820 nm reflection showed that the electron transfer of PSII was decreased, and PSI activity was increased in yellow T. grandis leaves. Transcriptome data showed that the unigenes involved in chlorophyll synthesis and the photosynthetic electron transport complex were downregulated in the leaves of mutant-type T. grandis compared to wild-type leaves, while there were no observable changes in carotenoid content and biosynthesis. These findings suggest that the downregulation of genes involved in chlorophyll synthesis leads to decreased chlorophyll content, resulting in both PSI activity and carotenoids having higher tolerance when acting as photo-protective mechanisms for coping with chlorophyll deficit and decrease in linear electron transport in PSII.

iTRAQ-Based Quantitative Proteomics Analysis Reveals the Mechanism of Golden-Yellow Leaf Mutant in Hybrid Paper Mulberry

Plant growth and development relies on the conversion of light energy into chemical energy, which takes place in the leaves. Chlorophyll mutant variations are important for studying certain physiological processes, including chlorophyll metabolism, chloroplast biogenesis, and photosynthesis. To uncover the mechanisms of the golden-yellow phenotype of the hybrid paper mulberry plant, this study used physiological, cytological, and iTRAQ-based proteomic analyses to compare the green and golden-yellow leaves of hybrid paper mulberry. Physiological results showed that the mutants of hybrid paper mulberry showed golden-yellow leaves, reduced chlorophyll, and carotenoid content, and increased flavonoid content compared with wild-type plants. Cytological observations revealed defective chloroplasts in the mesophyll cells of the mutants. Results demonstrated that 4766 proteins were identified from the hybrid paper mulberry leaves, of which 168 proteins displayed differential accumulations between the green and mutant leaves. The differentially accumulated proteins were primarily involved in chlorophyll synthesis, carotenoid metabolism, and photosynthesis. In addition, differentially accumulated proteins are associated with ribosome pathways and could enable plants to adapt to environmental conditions by regulating the proteome to reduce the impact of chlorophyll reduction on growth and survival. Altogether, this study provides a better understanding of the formation mechanism of the golden-yellow leaf phenotype by combining proteomic approaches.

Comparative transcriptome and microbial community sequencing provide insight into yellow-leaf phenotype of Camellia japonica

BACKGROUND

Leaf color variation is a common trait in plants and widely distributed in many plants. In this study, a leaf color mutation in Camellia japonica (cultivar named as Maguxianzi, M) was used as material, and the mechanism of leaf color variation was revealed by physiological, cytological, transcriptome and microbiome analyses.

RESULTS

The yellowing C. japonica (M) exhibits lower pigment content than its parent (cultivar named as Huafurong, H), especially chlorophyll (Chl) and carotenoid, and leaves of M have weaker photosynthesis. Subsequently, the results of transmission electron microscopy(TEM) exhibited that M chloroplast was accompanied by broken thylakoid membrane, degraded thylakoid grana, and filled with many vesicles. Furthermore, comparative transcriptome sequencing identified 3,298 differentially expressed genes (DEGs). KEGG annotation analysis results showed that 69 significantly enriched DEGs were involved in Chl biosynthesis, carotenoid biosynthesis, photosynthesis, and plant-pathogen interaction. On this basis, we sequenced the microbial diversity of the H and M leaves. The sequencing results suggested that the abundance of Didymella in the M leaves was significantly higher than that in the H leaves, which meant that M leaves might be infected by Didymella.

CONCLUSIONS

Therefore, we speculated that Didymella infected M leaves while reduced Chl and carotenoid content by damaging chloroplast structures, and altered the intensity of photosynthesis, thereby causing the leaf yellowing phenomenon of C. japonica (M). This research will provide new insights into the leaf color variation mechanism and lay a theoretical foundation for plant breeding and molecular markers.

Candidate reference genes for quantitative gene expression analysis in Lagerstroemia indica

Quantitative gene expression analysis by qPCR requires reference genes for normalization. Lagerstroemia indica (crape myrtle) is a popular ornamental plant in the world, but suitable endogenous reference genes are lacking. To find suitable reference genes, we evaluated the stabilities of nine candidate genes in six experimental data sets: six different tissues, three leaf colors, nine flower colors, and under three abiotic stresses (salt, drought, cold) using four statistical algorithms. A target gene LiMYB56 (homolog of Arabidopsis MYB56) was used to verify the authenticity and accuracy of the candidate reference genes. The results showed that the combination of two stably expressed reference genes, rather than a single reference gene, improved the accuracy of the qPCR. LiEF1α-2 + LiEF1α-3 was best for the tissue, salt treatment, and drought treatment sets; LiEF1α-2 + LiEF1α-1 was optimal for leaf color; LiEF1α-2 + LiACT7 was optimal for cold treatment; and LiUBC + LiEF1α-1 was best for the flower color set. Notably, LiEF1α-2 had high expression stability in all six experimental sets, implying it may be a good reference gene for expression studies in L. indica. Our results will facilitate future gene expression studies in L. indica.

Effect of chlorophyll biosynthesis-related genes on the leaf color in Hosta (Hosta plantaginea Aschers) and tobacco (Nicotiana tabacum L.)

BACKGROUND

'Regal Splendour' (Hosta variety) is famous for its multi-color leaves, which are useful resources for exploring chloroplast development and color changes. The expressions of chlorophyll biosynthesis-related genes (HrHEMA, HrPOR and HrCAO) in Hosta have been demonstrated to be associated with leaf color. Herein, we isolated, sequenced, and analyzed HrHEMA, HrPOR and HrCAO genes. Subcellular localization was also performed to determine the location of the corresponding enzymes. After plasmid construction, virus-induced gene silencing (VIGS) was carried out to reduce the expressions of those genes. In addition, HrHEMA-, HrPOR- and HrCAO-overexpressing tobacco plants were made to verify the genes function. Changes of transgenic tobacco were recorded under 2000 lx, 6000 lx and 10,000 lx light intensity. Additionally, the contents of enzyme 5-aminolevulinic acid (5-ALA), porphobilinogen (PBG), chlorophyll a and b (Chla and Chlb), carotenoid (Cxc), superoxide dismutase (SOD), peroxidase (POD), malondialdehyde (MDA), proline (Pro) and catalase (CAT) under different light intensities were evaluated.

RESULTS

The silencing of HrHEMA, HrPOR and HrCAO genes can induce leaf yellowing and chloroplast structure changes in Hosta. Specifically, leaves of Hosta with HrCAO silencing were the most affected, while those with HrPOR silencing were the least affected. Moreover, all three genes in tobacco were highly expressed, whereas no expression was detected in wild-type (WT). However, the sensitivities of the three genes to different light intensities were different. The highest expression level of HrHEMA and HrPOR was detected under 10,000 lx of illumination, while HrCAO showed the highest expression level under 6000 lx. Lastly, the 5-ALA, Chla, Cxc, SOD, POD, MDA, Pro and CAT contents in different transgenic tobaccos changed significantly under different light intensities.

CONCLUSION

The overexpression of these three genes in tobacco enhanced photosynthesis by accumulating chlorophyll content, but the influential level varied under different light intensities. Furthermore, HrHEMA-, HrPOR- and HrCAO- overexpressing in tobacco can enhance the antioxidant capacity of plants to cope with stress under higher light intensity. However, under lower light intensity, the antioxidant capacity was declined in HrHEMA-, HrPOR- and HrCAO- overexpressing tobaccos.

Integrated Physiological and Transcriptomic Analyses Reveal a Regulatory Network of Anthocyanin Metabolism Contributing to the Ornamental Value in a Novel Hybrid Cultivar of Camellia Japonica

Camellia japonica is a plant species with great ornamental and gardening values. A novel hybrid cultivar Chunjiang Hongxia (Camellia japonica cv. Chunjiang Hongxia, CH) possesses vivid red leaves from an early growth stage to a prolonged period and is, therefore, commercially valuable. The molecular mechanism underlying this red-leaf phenotype in C. japonica cv. CH is largely unknown. Here, we investigated the leaf coloration process, photosynthetic pigments contents, and different types of anthocyanin compounds in three growth stages of the hybrid cultivar CH and its parental cultivars. The gene co-expression network and differential expression analysis from the transcriptome data indicated that the changes of leaf color were strongly correlated to the anthocyanin metabolic processes in different leaf growth stages. Genes with expression patterns associated with leaf color changes were also discussed. Together, physiological and transcriptomic analyses uncovered the regulatory network of metabolism processes involved in the modulation of the ornamentally valuable red-leaf phenotype and provided the potential candidate genes for future molecular breeding of ornamental plants such as Camellia japonica.

Screening of key genes responsible for Pennisetum setaceum 'Rubrum' leaf color using transcriptome sequencing

Pennisetum setaceum 'Rubrum' is an ornamental grass plant that produces purple leaves in high-light environments and light purple or green leaves in low-light environments, the latter of which greatly reduces its aesthetic appeal. Therefore, we aimed to identify the key genes associated with leaf coloration and elucidate the molecular mechanisms involved in the color changes in P. setaceum 'Rubrum' leaves. We performed transcriptome sequencing of P. setaceum 'Rubrum' leaves before and after shading. A total of 19,043 differentially expressed genes were identified, and the numbers of upregulated and downregulated genes at T1 stage, when compared with their expression at the T0 stage, were 10,761 and 8,642, respectively. The possible pathways that determine P. setaceum 'Rubrum' leaf color included flavonoid biosynthesis, flavone and flavonol biosynthesis, and carotenoid biosynthesis. There were 31 differentially expressed genes related to chlorophyll metabolism, of which 21 were related to chlorophyll biosynthesis and 10 to chlorophyll degradation, as well as three transcription factors that may be involved in the regulation of chlorophyll degradation. There were 31 key enzyme genes involved in anthocyanin synthesis and accumulation in P. setaceum 'Rubrum' leaves, with four transcription factors that may be involved in the regulation of anthocyanin metabolism. The transcriptome data were verified and confirmed reliable by real-time fluorescence quantitative PCR analysis. These findings provide a genetic basis for improving leaf color in P. setaceum 'Rubrum.'

Label-free comparative proteomic and physiological analysis provides insight into leaf color variation of the golden-yellow leaf mutant of Lagerstroemia indica

GL1 is a golden-yellow leaf mutant that cultivated from natural bud-mutation of Lagerstroemia indica and has a very low level of photosynthetic pigment under sunlight. GL1 can gradually increase its pigment content and turn into pale-green leaf when shading under sunshade net (referred as Re-GL1). The mechanisms that cause leaf color variation are complicated and are not still unclear. Here, we have used a label-free comparative proteomics to investigate differences in proteins abundance and analyze the specific biological process associated with mechanisms of leaf color variation in GL1. A total of 245 and 160 proteins with different abundance were identified in GL1 vs WT and GL1 vs Re-GL1, respectively. Functional classification analysis revealed that the proteins with different abundance mainly related to photosynthesis, heat shock proteins, ribosome proteins, and oxidation-reduction. The proteins that the most significantly contributed to leaf color variation were photosynthetic proteins of PSII and PSI, which directly related to photooxidation and determined the photosynthetic performance of photosystem. Further analysis demonstrated that low jasmonic acid content was needed to golden-yellow leaf GL1. These findings lay a solid foundation for future studies into the molecular mechanisms that underlie leaf color formation of GL1. BIOLOGICAL SIGNIFICANCE: The natural bud mutant GL1 of L. indica is an example through changing leaf color to cope with complex environment. However, the molecular mechanism of leaf color variation are largely elusive. The proteins with different abundance identified from a label-free comparative proteomics revealed a range of biological processes associated with leaf color variation, including photosynthesis, oxidation-reduction and jasmonic acid signaling. The photooxidation and low level of jasmonic acid played a primary role in GL1 adaptation in golden-yellow leaf. These findings provide possible pathway or signal for the molecular mechanism associated with leaf color formation and as a valuable resource for signal transaction of chloroplast.

Mutation Mechanism of Leaf Color in Plants: A Review

Color mutation is a common, easily identifiable phenomenon in higher plants. Color mutations usually affect the photosynthetic efficiency of plants, resulting in poor growth and economic losses. Therefore, leaf color mutants have been unwittingly eliminated in recent years. Recently, however, with the development of society, the application of leaf color mutants has become increasingly widespread. Leaf color mutants are ideal materials for studying pigment metabolism, chloroplast development and differentiation, photosynthesis and other pathways that could also provide important information for improving varietal selection. In this review, we summarize the research on leaf color mutants, such as the functions and mechanisms of leaf color mutant-related genes, which affect chlorophyll synthesis, chlorophyll degradation, chloroplast development and anthocyanin metabolism. We also summarize two common methods for mapping and cloning related leaf color mutation genes using Map-based cloning and RNA-seq, and we discuss the existing problems and propose future research directions for leaf color mutants, which provide a reference for the study and application of leaf color mutants in the future.

Biochemical and Comparative Transcriptome Analyses Reveal Key Genes Involved in Major Metabolic Regulation Related to Colored Leaf Formation in Osmanthus fragrans 'Yinbi Shuanghui' during Development

Osmanthus fragrans 'Yinbi Shuanghui' not only has a beautiful shape and fresh floral fragrance, but also rich leaf colors that change, making the tree useful for landscaping. In order to study the mechanisms of color formation in O. fragrans 'Yinbi Shuanghui' leaves, we analyzed the colored and green leaves at different developmental stages in terms of leaf pigment content, cell structure, and transcriptome data. We found that the chlorophyll content in the colored leaves was lower than that of green leaves throughout development. By analyzing the structure of chloroplasts, the colored leaves demonstrated more stromal lamellae and low numbers of granum thylakoid. However, there was a large number of plastoglobuli. Using transcriptome sequencing, we demonstrated that the expression of differentially expressed genes (DEGs) involved in chlorophyll degradation was upregulated, i.e., heme oxygennase-1 (HO1), pheophorbide a oxidase (PAO), and chlorophyllase-2 (CLH2), affecting the synthesis of chlorophyll in colored leaves. The stay-green gene (SGR) was upregulated in colored leaves. Genes involved in carotenoid synthesis, i.e., phytoene synthase 1 (PSY1) and 1-Deoxyxylulose-5-phosphate synthase (DXS), were downregulated in colored leaves, impeding the synthesis of carotenoids. In the later stage of leaf development, the downregulated expression of Golden2-Like (GLK) inhibited chloroplast development in colored leaves. Using weighted gene co-expression network analysis (WGCNA) to investigate the correlation between physiological indicators and DEGs, we chose the modules with the highest degree of relevance to chlorophyll degradation and carotenoid metabolism. A total of five genes (HSFA2, NFYC9, TCP20, WRKY3, and WRKY4) were identified as hub genes. These analyses provide new insights into color formation mechanisms in O. fragrans 'Yinbi Shuanghui' leaves at the transcriptional level.

The identification of key candidate genes mediating yellow seedling lethality in a Lilium regale mutant

Leaf color mutants are ideal materials for exploring plant photosynthesis mechanisms, chlorophyll biosynthetic pathways and chloroplast development. The yellow seedling lethal mutant lrysl1 was discovered from self-bred progenies of Lilium regale; however, the mechanism of leaf color mutation remains unclear. In this study, the ultrastructural and physiological features and de novo RNA-Seq data of a L. regale leaf color mutant and wild-type L. regale were investigated. Genetic analysis indicated that the characteristics of the lrysl1 mutant were controlled by a recessive nuclear gene. The chlorophyll a, chlorophyll b and carotenoid contents in the mutant leaves were lower than those in the wild-type leaves. Furthermore, the contents of the chlorophyll precursors aminolevulinic acid (ALA), porphobilinogen (PBG), protoporphyrin IX (ProtoIX), Mg-protoporphyrin IX (Mg-ProtoIX), and protochlorophyll (Pchl) decreased significantly in mutant leaves. Transcriptome data from the mutant and wild type showed that a total of 892 differentially expressed genes were obtained, of which 668 and 224 were upregulated genes and downregulated genes in the mutant, respectively. Almost all genes in the photosynthesis pathway and chlorophyll biosynthetic pathway were downregulated in the mutant, which corroborated the differences in the physiological features mentioned above. Further research indicated that the chloroplasts of the mutant leaves exhibited an abnormal morphology and distribution and that the expression of a gene related to chloroplast development was downregulated. It was concluded that abnormal chloroplast development was the main cause of leaf color mutation in the mutant lrysl1 and that LrGLK was a gene related to chloroplast development in L. regale. This research provides a foundation for further research on the mechanism by which LrGLK regulates chloroplast development in L. regale.

Pigment variation and transcriptional response of the pigment synthesis pathway in the S2309 triple-color ornamental kale (Brassica oleracea L. var. acephala) line

Ornamental kale is popular because of its colorful leaves and few studies have investigated the mechanism of color changes. In this study, an ornamental kale line (S2309) with three leaf colors was developed. Analysis of the anthocyanin, chlorophyll, and carotenoid contents and RNA-seq were performed on the three leaf color types. There was less chlorophyll in the white leaves and purple leaves than in the green leaves, and the anthocyanin content was greatest in the purple leaves. All the downregulated DEGs related to chlorophyll metabolism were detected only in the S2309_G vs. S2309_W comparison, which indicated that the decrease in chlorophyll content was caused mainly by the inhibition of chlorophyll biosynthesis during the leaf color change from green to white. Moreover, the expression of 19 DEGs involved in the anthocyanin biosynthesis pathway was upregulated. These results provide new insight into the mechanisms underlying the three-color formation.

Widely Targeted Metabolomic and Transcriptomic Analyses of a Novel Albino Tea Mutant of “Rougui”

Albino tea mutants with specific shoot colors (white or yellow) have received increasing attention from researchers due to their unique phenotypes, beneficial metabolites, and special flavor. In this study, novel natural yellow leaf mutants of the same genetic background of “Rougui” were obtained, and the transcriptome and metabolite profiles of the yellow leaf mutant (YR) and original green cultivar (GR) were investigated. A total of 130 significantly changed metabolites (SCMs) and 55 differentially expressed genes (DEGs) were identified in YR compared to GR. The leaf coloration of YR was primarily affected by pigment metabolism including of chlorophyll, carotenoids, and flavonoids, and the co-expression of three heat shock proteins (HSPs) and four heat shock transcription factors (HSFs) may also regulate leaf coloration by affecting chloroplast biogenesis. Of the 130 SCMs, 103 showed clearly increased abundance in YR, especially nucleotides and amino acids and their derivatives and flavonoids, suggesting that YR may be an ideal albino tea germplasm for planting and breeding. Our results may help to characterize the leaf coloration and metabolic mechanism of albino tea germplasm.

Color characteristics, pigment accumulation and biosynthetic analyses of leaf color variation in herbaceous peony (Paeonia lactiflora Pall.)

Herbaceous peony (Paeonia lactiflora Pall.) is one of the color-leaved ornamental spring plants, with graceful appearance and splendid color. However, the underlying mechanism of this coloration variation from purple to green has not been studied in P. lactiflora. In th study, the leaves in purple, purple-green, and green stages were compared in terms of anatomical, physiological, and molecular. We found that the variation of leaf color from purple to green was mainly determined by the change in pigments distributed in the leaf surface. Physiological experiments showed a significant increase in chlorophyll contents and a notable reduction in anthocyanin contents in leaves from the purple to green stages. We further found that the anthocyanin biosynthesis-related dihydroflavonol 4-reductase (DFR) gene and anthocyanin synthase (ANS) gene as well as chlorophyll biosynthesis-related glutamyl-tRNA reductase (HEMA) gene showed a decreased trend in leaves from purple to green stages, whereas the chlorophyll degradation-related chlorophyll b reductase (NYC) gene showed a rising trend. Alteration of DFR and ANS gene expression might reduce anthocyanin accumulation, whereas increased HEMA gene expression would enhance chlorophyll biosynthesis and reduced NYC gene expression would inhibit chlorophyll degradation. Consequently, reduction in anthocyanins and enhanced deposition of chlorophylls resulted in leaf coloration variation from purple to green in P. lactiflora, which could improve our understanding of its mechanism for further studies.

Physiological and Anatomical Differences and Differentially Expressed Genes Reveal Yellow Leaf Coloration in Shumard Oak

Shumard oak (Quercus shumardii Buckley) is a traditional foliage plant, but little is known about its regulatory mechanism of yellow leaf coloration. Here, the yellow leaf variety of Q. shumardii named 'Zhongshan Hongjincai' (identified as 'ZH' throughout this work) and a green leaf variety named 'Shumard oak No. 23' (identified as 'SO' throughout this work) were compared. 'ZH' had lower chlorophyll content and higher carotenoid content; photosynthetic characteristics and chlorophyll fluorescence parameters were also lower. Moreover, the mesophyll cells of 'ZH' showed reduced number of chloroplasts and some structural damage. In addition, transcriptomic analysis identified 39,962 differentially expressed genes, and their expression levels were randomly verified. Expressions of chlorophyll biosynthesis-related glumly-tRNA reductase gene and Mg-chelatase gene were decreased, while pheophorbide a oxygenase gene associated with chlorophyll degradation was up-regulated in 'ZH'. Simultaneously, carotenoid isomerase gene, z-carotene desaturase gene, violaxanthin de-epoxidase gene and zeaxanthin epoxidase gene involved in carotenoid biosynthesis were up-regulated in 'ZH'. These gene expression changes were accompanied by decreased chlorophyll content and enhanced carotenoid accumulation in 'ZH'. Consequently, changes in the ratio of carotenoids to chlorophyll could be driving the yellow leaf coloration in Q. shumardii.

Transcriptional profiling of long noncoding RNAs associated with leaf-color mutation in Ginkgo biloba L

BACKGROUND

Long noncoding RNAs (lncRNAs) play an important role in diverse biological processes and have been widely studied in recent years. However, the roles of lncRNAs in leaf pigment formation in ginkgo (Ginkgo biloba L.) remain poorly understood.

RESULTS

In this study, lncRNA libraries for mutant yellow-leaf and normal green-leaf ginkgo trees were constructed via high-throughput sequencing. A total of 2044 lncRNAs were obtained with an average length of 702 nt and typically harbored 2 exons. We identified 238 differentially expressed lncRNAs (DELs), 32 DELs and 49 differentially expressed mRNAs (DEGs) that constituted coexpression networks. We also found that 48 cis-acting DELs regulated 72 target genes, and 31 trans-acting DELs regulated 31 different target genes, which provides a new perspective for the regulation of the leaf-color mutation. Due to the crucial regulatory roles of lncRNAs in a wide range of biological processes, we conducted in-depth studies on the DELs and their targets and found that the chloroplast thylakoid membrane subcategory and the photosynthesis pathways (ko00195) were most enriched, suggesting their potential roles in leaf coloration mechanisms. In addition, our correlation analysis indicates that eight DELs and 68 transcription factors (TFs) might be involved in interaction networks.

CONCLUSIONS

This study has enriched the knowledge concerning lncRNAs and provides new insights into the function of lncRNAs in leaf-color mutations, which will benefit future selective breeding of ginkgo.

Transcriptome analysis based on a combination of sequencing platforms provides insights into leaf pigmentation in Acer rubrum

BACKGROUND

Red maple (Acer rubrum L.) is one of the most common and widespread trees with colorful leaves. We found a mutant with red, yellow, and green leaf phenotypes in different branches, which provided ideal materials with the same genetic relationship, and little interference from the environment, for the study of complex metabolic networks that underly variations in the coloration of leaves. We applied a combination of NGS and SMRT sequencing to various red maple tissues.

RESULTS

A total of 125,448 unigenes were obtained, of which 46 and 69 were thought to be related to the synthesis of anthocyanins and carotenoids, respectively. In addition, 88 unigenes were presumed to be involved in the chlorophyll metabolic pathway. Based on a comprehensive analysis of the pigment gene expression network, the mechanisms of leaf color were investigated. The massive accumulation of Cy led to its higher content and proportion than other pigments, which caused the redness of leaves. Yellow coloration was the result of the complete decomposition of chlorophyll pigments, the unmasking of carotenoid pigments, and a slight accumulation of Cy.

CONCLUSIONS

This study provides a systematic analysis of color variations in the red maple. Moreover, mass sequence data obtained by deep sequencing will provide references for the controlled breeding of red maple.

Physiological and Transcriptome Analysis of a Yellow-Green Leaf Mutant in Birch (Betula platyphylla × B. Pendula)

Chlorophyll (Chl)-deficient mutants are ideal materials for the study of Chl biosynthesis, chloroplast development, and photosynthesis. Although the genes encoding key enzymes related to Chl biosynthesis have been well-characterized in herbaceous plants, rice (Oryza sativa L.), Arabidopsis (Arabidopsis thaliana), and maize (Zea mays L.), yellow-green leaf mutants have not yet been fully studied in tree species. In this work, we explored the molecular mechanism of the leaf color formation in a yellow-green leaf mutant (yl). We investigated the differentially expressed genes (DEGs) between yl and control plants (wild type birch (WT) and BpCCR1 overexpression line 11, (C11)) by transcriptome sequencing. Approximately 1163 genes (874 down-regulated and 289 up-regulated) and 930 genes (755 down-regulated and 175 up-regulated) were found to be differentially expressed in yl compared with WT and C11, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis for DEGs revealed that photosynthesis antenna proteins represent the most significant enriched pathway. The expressions of photosynthesis antenna proteins are crucial to the leaf color formation in yl. We also found that Chl accumulate, leaf anatomical structure, photosynthesis, and growth were affected in yl. Taken together, our results not only provide the difference of phenomenal, physiological, and gene expression characteristics in leaves between yl mutant and control plants, but also provide a new insight into the mutation underlying the chlorotic leaf phenotype in birch.

Comparative transcriptome profiling of genes and pathways involved in leaf-patterning of Clivia miniata var. variegata

Clivia miniata var. variegata (Cmvv) typically possesses yellow- and green-striped leaves. The striped plant not only has a high ornamental value but also be suitable for photosynthesis and chloroplast development research. Our previous study had revealed that yellow stripes (YSs) of Cmvv leaves contain chlorophyll-less ineffective chloroplasts. However, mechanism of Cmvv variegation is yet to be investigated. In the study, transcriptomes of both the YSs and green stripes (GSs) from single Cmvv leaves were compared using high-throughput sequencing. A total of 688 differential expression genes (DEGs) were identified based on biological replications. The qRT-PCR results indicated that transcriptome profiles accurately reflected global transcriptome differences between YSs and GSs. Subcellular localization analysis suggested that 56 DEG proteins were targeted to chloroplasts, and might be involved in anterograde signaling and leaf patterning. Moreover, the DEGs were mostly enriched in photosynthesis and plant-pathogen interaction KEGG pathways. Meanwhile, there should be coordination interaction between the two pathways. Seven of the eight DEGs involved in photosynthesis KEGG pathway were chloroplast-encoded genes and distributed among different cistrons of chloroplast DNA (cpDNA) large single copy regions (LSC) which are more prone to mutation. It was proposed that the YSs were caused by mutation(s) in cpDNA LSC. Thus, when the primary zygote of Cmvv was chimeric in LSC, leaf might be yellow- and green-striped. The study would give new insights into plant variegation and offers candidate genes to guide future research attempting to breed variegated plants.

Candidate Genes for Yellow Leaf Color in Common Wheat (Triticum aestivum L.) and Major Related Metabolic Pathways according to Transcriptome Profiling

The photosynthetic capacity and efficiency of a crop depends on the biosynthesis of photosynthetic pigments and chloroplast development. However, little is known about the molecular mechanisms of chloroplast development and chlorophyll (Chl) biosynthesis in common wheat because of its huge and complex genome. Ygm, a spontaneous yellow-green leaf color mutant of winter wheat, exhibits reduced Chl contents and abnormal chloroplast development. Thus, we searched for candidate genes associated with this phenotype. Comparative transcriptome profiling was performed using leaves from the yellow leaf color type (Y) and normal green color type (G) of the Ygm mutant progeny. We identified 1227 differentially expressed genes (DEGs) in Y compared with G (i.e., 689 upregulated genes and 538 downregulated genes). Gene ontology and pathway enrichment analyses indicated that the DEGs were involved in Chl biosynthesis (i.e., magnesium chelatase subunit H (CHLH) and protochlorophyllide oxidoreductase (POR) genes), carotenoid biosynthesis (i.e., β-carotene hydroxylase (BCH) genes), photosynthesis, and carbon fixation in photosynthetic organisms. We also identified heat shock protein (HSP) genes (sHSP, HSP70, HSP90, and DnaJ) and heat shock transcription factor genes that might have vital roles in chloroplast development. Quantitative RT-PCR analysis of the relevant DEGs confirmed the RNA-Seq results. Moreover, measurements of seven intermediate products involved in Chl biosynthesis and five carotenoid compounds involved in carotenoid-xanthophyll biosynthesis confirmed that CHLH and BCH are vital enzymes for the unusual leaf color phenotype in Y type. These results provide insights into leaf color variation in wheat at the transcriptional level.

Reference gene selection for qRT-PCR analysis of flower development in Lagerstroemia indica and L. speciosa

Quantitative real-time polymerase chain reaction (qRT-PCR) is a prevalent method for gene expression analysis, depending on the stability of the reference genes for data normalization. Lagerstroemia indica and L. speciosa are popular ornamental plants which are famous for the long flowering period. However, no systematic studies on reference genes in Lagerstroemia have yet been conducted. In the present study, we selected nine candidate reference genes (GAPDH, TUA, TUB, 18S, RPII, EF-1α, ATC, EIF5A and CYP) and evaluated their expression stability in different tissues during floral development of L. indica and L. speciosa using four algorithms (geNorm, NormFinder, BestKeeper and, RefFinder). Results showed that RPII and EF-1α were the most stably expressed and suitable reference genes for both of Lagerstroemia species. Moreover, ACT exhibited high expression stability in L. indica and GAPDH was a suitable reference gene for L. speciosa in different flower development stages. TUB was an unsuitable reference gene for gene expression normalization due to significant variations in expression across all samples. Finally, we verified the reliability of the selected candidate reference genes by amplifying an AGAMOUS homolog (LsAG1) of Arabidopsis thaliana. This study provides a list of suitable reference genes, thereby broadening the genetic basis of the gene expression patterns in Lagerstroemia species.

Cytological, physiological, and transcriptomic analyses of golden leaf coloration in Ginkgo biloba L

Ginkgo biloba is grown worldwide as an ornamental plant for its golden leaf color. However, the regulatory mechanism of leaf coloration in G. biloba remains unclear. Here, we compared G. biloba gold-colored mutant leaves and normal green leaves in cytological, physiological and transcriptomic terms. We found that chloroplasts of the mutant were fewer and smaller, and exhibited ruptured thylakoid membranes, indistinct stromal lamellae and irregularly arranged vesicles. Physiological experiments also showed that the mutant had a lower chlorophyll, lower flavonoid and higher carotenoid contents (especially lutein). We further used transcriptomic sequencing to identify 116 differentially expressed genes (DEGs) and 46 transcription factors (TFs) involved in chloroplast development, chlorophyll metabolism, pigment biosynthesis and photosynthesis. Among these, the chlorophyll biosynthesis-related PPO showed down-regulation, while chlorophyll degradation-related NYC/NOL had up-regulated expression in mutant leaves. Z-ISO, ZDS, and LCYE, which are involved in carotenoid biosynthesis were up-regulated. Quantitative real-time PCR (RT-qPCR) further confirmed the altered expression levels of these genes at three stages. The alteration of PPO and NYC/NOL gene expression might affect chlorophyll biosynthesis and promote degradation of chlorophyll b to chlorophyll a, while the up-regulated genes Z-ISO, ZDS and LCYE enhanced carotenoid accumulation. Consequently, changes in the ratio of carotenoids to chlorophylls were the main factors driving the golden leaf coloration in the mutant G. biloba.

Characterization and Complementation of a Chlorophyll-Less Dominant Mutant GL1 in Lagerstroemia indica

Crape myrtle (Lagerstroemia indica) is a woody ornamental plant popularly grown because of its long-lasting, midsummer blooms and beautiful colors. The GL1 dominant mutant is the first chlorophyll-less mutant identified in crape myrtle. It was obtained from a natural yellow leaf bud mutation. We previously revealed that leaf color of the GL1 mutant is affected by light intensity. However, the mechanism of the GL1 mutant on light response remained unclear. The acclimation response of mutant and wild-type (WT) plants was assessed in a time series after transferring from low light (LL) to high light (HL) by analyzing chlorophyll synthesis precursor content, photosynthetic performance, and gene expression. In LL conditions, coproporphyrinogen III (Coprogen III) content had the greatest amount of accumulation in the mutant compared with WT, increasing by 100%. This suggested that the yellow leaf phenotype of the GL1 dominant mutant might be caused by disruption of coproporphyrinogen III oxidase (CPO) biosynthesis. Furthermore, the candidate gene, oxygen-independent CPO (HEMN), might only affect expression of upstream genes involved in chlorophyll metabolism in the mutant. Moreover, two genes, photosystem II (PSII) 10 kDa protein (psbR) and chlorophyll a/b binding protein gene (CAB1), had decreased mRNA levels in the GL1 mutant within the first 96 h following LL/HL transfer compared with the WT. Hierarchical clustering revealed that these two genes shared a similar expression trend as the oxygen-dependent CPO (HEMF). These findings provide evidence that GL1 is highly coordinated with PSII stability and chloroplast biogenesis.