Regulation Of Chlorophyll Biosynthesis Research Articles

Irregular green netting of eggplant fruit peel: a domestication trait controlled by SmGLK2 with potential for fruit colour diversification.

The distribution of chlorophylls in eggplant (Solanum melongena) peel exhibits either a uniform pattern or an irregular green netting. The latter, manifested as a gradient of dark green netting intensified in the proximal part of the fruit on a pale green background, is common in wild relatives and some eggplant landraces. Despite the selection of uniform chlorophylls during domestication, the netting pattern contributes to a greater diversity of fruit colours. Here, we have used over 2,300 individuals from different populations, including a multi-parental MAGIC population for candidate genomic region identification, an F2 population for BSA-Seq, and advanced backcrosses for edges-to-core fine-mapping, to identify SmGLK2 gene as responsible for the irregular netting in eggplant fruits. We have also analysed the gene sequence of 178 S. melongena accessions and 22 wild relative species for tracing the evolutionary changes that the gene has undergone during domestication. Three different mutations were identified leading to the absence of netting. The main causative indel induces a premature stop codon disrupting the protein conformation and function, which was confirmed by western blotting analysis and confocal microscopy observations. SmGLK2 has a major role in regulating chlorophyll biosynthesis in eggplant fruit peel.

Temperature-dependent jumonji demethylase modulates flowering time by targeting H3K36me2/3 in Brassica rapa

Global warming has a severe impact on the flowering time and yield of crops. Histone modifications have been well-documented for their roles in enabling plant plasticity in ambient temperature. However, the factor modulating histone modifications and their involvement in habitat adaptation have remained elusive. In this study, through genome-wide pattern analysis and quantitative-trait-locus (QTL) mapping, we reveal that BrJMJ18 is a candidate gene for a QTL regulating thermotolerance in thermotolerant B. rapa subsp. chinensis var. parachinensis (or Caixin, abbreviated to Par). BrJMJ18 encodes an H3K36me2/3 Jumonji demethylase that remodels H3K36 methylation across the genome. We demonstrate that the BrJMJ18 allele from Par (BrJMJ18Par) influences flowering time and plant growth in a temperature-dependent manner via characterizing overexpression and CRISPR/Cas9 mutant plants. We further show that overexpression of BrJMJ18Par can modulate the expression of BrFLC3, one of the five BrFLC orthologs. Furthermore, ChIP-seq and transcriptome data reveal that BrJMJ18Par can regulate chlorophyll biosynthesis under high temperatures. We also demonstrate that three amino acid mutations may account for function differences in BrJMJ18 between subspecies. Based on these findings, we propose a working model in which an H3K36me2/3 demethylase, while not affecting agronomic traits under normal conditions, can enhance resilience under heat stress in Brassica rapa.

Mechanisms governing melon fruit skin pigmentation: Insights from transcriptome sequencing and whole-genome bisulfite sequencing analyses

Fruit skin color is a critical agronomic trait determining fruit quality, but the mechanisms governing melon (Cucumis melo L.) fruit skin pigmentation remain inadequately characterized. We performed cytological, transcriptomic, and whole-genome bisulfite sequencing (WGBS) comparative analyses on two near-isogenic lines (NILs) at different developmental stages: the green-skinned (GS) and white-skinned (WS) melon. The enriched functions among the 536 identified differentially expressed genes (DEGs) were related to chloroplast development, pigment metabolism, and photosynthetic pathway. The genes in these pathways were downregulated in the WS line, potentially contributing to the decreased chlorophyll content and abnormal chloroplast development in WS. WGBS analysis revealed that the levels of genomic DNA methylation in WS progressively exceeded those in GS as the fruits developed. The integrated analysis of the transcriptome and methylome identified DMR-associated DEGs (CHLI, CRD1, PORA, and HCAR) involved in chlorophyll metabolism. Notably, PORA exhibited downregulated expression and was hypermethylated in WS fruits during two developmental stages, showing a coordinated expression with the chlorophyll contents in developing WS and GS fruits. Furthermore, we identified a transcription factor gene, MELO3C011576, that was closely associated with the expression of PORA and chlorophyll levels across three developmental stages in both NILs. We speculate that PORA positively regulates chlorophyll biosynthesis in the two NILs, with its expression may be co-controlled by DNA methylation and transcription factors.

GhFP positively regulates chlorophyll content and seedling biomass in upland cotton

Cotton is one of the most important cash crops worldwide. Chlorophyll is a critical photosynthetic pigment in plants, which could significantly affect the growth and development of cotton. In this study, one insertion mutant, ZD131, was found to have darker leaves and higher chlorophyll content than wild-type (WT) at the seedling and flowering stages. The chlorophyll contents were also higher in F1 and F2 heterozygous plants crossed by ZD131 and WT than that in WT. Through genome resequencing of mutant ZD131, a coding gene Ghir_D07G020490, we named it GhFP, was found at 2347 bp downstream of the insertion site in ZD131, which has not been studied yet. GhFP was localized in the cytoplasm and expressed higher in ZD131 than that in WT. Furthermore, virus-induced gene silencing (VIGS) of GhFP in cotton and overexpression of GhFP in Arabidopsis verified that GhFP could positively regulate the chlorophyll content and biomass. Therefore, this study revealed that a novel gene GhFP could regulate chlorophyll biosynthesis and biomass accumulation, which laid a theoretical foundation for understanding the regulatory mechanism of chlorophyll accumulation and provided essential gene resources for cotton genetic improvement.

Characterization and fine mapping of a yellow leaf gene regulating chlorophyll biosynthesis and chloroplast development in cotton (Gossypium arboreum)

Chlorophyll biosynthesis and chloroplast development are essential for photosynthesis and plant growth. Gossypium arboreum, a valuable source of genetic variation for cotton improvement, remains poorly studied for the mechanisms regulating chlorophyll biosynthesis and chloroplast development. Here we created a G. arboreum etiolated leaf and stuntedness (els) mutant that displayed a distinct yellow color of leaves, bracts and stems throughout the whole growth, where chlorophyll accumulation in leaves was reduced and chloroplast development was delayed. The GaCHLH gene, which encodes the H subunit of magnesium chelatase (Mg-chelatase), was screened by MutMap and KASP analysis. Compared to GaCHLH, the gene Gachlh of the mutant had a single nucleotide transition (G to A) at 1549 bp, which causes the substitution of a glycine (G) by a serine (S) at the 517th amino acid, resulting in an abnormal secondary structure of the Gachlh protein. GaCHLH-silenced SXY1 and ZM24 plants exhibited a lower GaCHLH expression level, a lower chlorophyll content, and the yellow-leaf phenotype. Gachlh expression affected the expression of key genes in the tetrapyrrole pathway. GaCHLH and Gachlh were located in the chloroplasts and that alteration of the mutation site did not affect the final target position. The BiFC assay result indicated that Gachlh could not bind to GaCHLD properly, which prevented the assembly of Mg-chelatase and thus led to the failure of chlorophyll synthesis. In this study, the Gachlh gene of G. arboreum els was finely localized and identified for the first time, providing new insights into the chlorophyll biosynthesis pathway in cotton.

GOLDEN 2-LIKE transcription factors regulate chlorophyll biosynthesis and flavonoid accumulation in response to UV-B in tea plants

Flavonoids are critical secondary metabolites that determine the health benefits and flavor of tea, while chlorophylls are important contributors to the appearance of tea. However, transcription factors (TFs) that can integrate both chlorophyll biosynthesis and flavonoid accumulation in response to specific light signals are rarely identified. In this study, we report that the GOLDEN 2-LIKE TF pair, CsGLK1 and CsGLK2, orchestrate UV-B-induced responses in the chlorophyll biosynthesis and flavonoid accumulation of tea leaves. The absence of solar UV-B reduced the transcriptional expression of CsGLKs in the tea leaves and was highly correlated with a decrease in flavonoid levels (especially flavonol glycosides) and the expression of genes and TFs involved in chlorophyll biosynthesis and flavonoid accumulation. In vivo and in vitro molecular analyses showed that CsGLKs could be regulated by the UV-B signal mediator CsHY5, and could directly bind to the promoters of gene and TF involved in light-harvesting (CsLhcb), chlorophyll biosynthesis (CsCHLH, CsHEMA1, and CsPORA), and flavonoid accumulation (CsMYB12, CsFLSa, CsDFRa, and CsLARa), eventually leading to UV-B-induced responses in the chlorophylls and flavonoids of tea leaves. Furthermore, UV-B exposure increased the levels of total flavonoids, CsGLK1 protein, and expression of CsGLKs and target genes in the tea leaves. These results indicate that CsGLKs may modulate tea leaf characteristics by regulating chlorophyll biosynthesis and flavonoid accumulation in response to solar UV-B. As the first report on UV-B-induced changes in flavonoid and chlorophyll regulation mediated by CsGLKs, this study improves our understanding of the environmental regulations regarding tea quality and sheds new light on UV-B-induced flavonoid responses in higher plants.

OsDXR interacts with OsMORF1 to regulate chloroplast development and the RNA editing of chloroplast genes in rice

Plant chlorophyll biosynthesis and chloroplast development are two complex processes regulated by exogenous and endogenous factors. In this study, we identified OsDXR , a gene expressing a reductoisomerase that positively regulates chlorophyll biosynthesis and chloroplast development in rice. OsDXR knock-out lines displayed the albino phenotype and could not complete the whole life cycle process. OsDXR was highly expressed in rice leaves, and subcellular localization indicated that OsDXR was a chloroplast protein. Many genes involved in chlorophyll biosynthesis and chloroplast development were differentially expressed in the OsDXR knock-out lines compared to the wild type. Moreover, we found that the RNA editing efficiency of ndhA -1019 and rpl2 -1 were significantly reduced in the OsDXR knock-out lines. Furthermore, OsDXR interacted with the RNA editing factor OsMORF1 in a yeast two-hybrid screen and bimolecular fluorescence complementation assay. We demonstrate that disruption of the plastidial 2-C-methyl-derythritol-4-phosphate pathway results in defects in chloroplast development and RNA editing of chloroplast genes.

Regulation of chlorophyll biosynthesis by light-dependent acetylation of NADPH:protochlorophyll oxidoreductase A in Arabidopsis

Chlorophylls are the major pigments that harvest light energy during photosynthesis in plants. Although reactions in chlorophyll biogenesis have been largely known, little attention has been paid to the post-translational regulation mechanism of this process. In this study, we found that four lysine sites (K128/340/350/390) of NADPH:protochlorophyllide oxidoreductase A (PORA), which catalyzes the only light-triggered step in chlorophyll biosynthesis, were acetylated after dark-grown seedlings transferred to light via acetylomics analysis. Etiolated seedlings with K390 mutation of PORA had a lower greening rate and decreased PORA acetylation after illumination. Importantly, K390 of PORA was found extremely conserved in plants and cyanobacteria via bioinformatics analysis. We further demonstrated that the acetylation level of PORA was increased by exposing the dark-grown seedlings to the histone deacetylase (HDAC) inhibitor TSA. Thus, the HDACs probably regulate the acetylation of PORA, thereby controlling this non-histone substrate to catalyze the reduction of Pchlide to produce chlorophyllide, which provides a novel regulatory mechanism by which the plant actively tunes chlorophyll biosynthesis during the conversion from skotomorphogenesis to photomorphogenesis.

Functional analysis of CqPORB in the regulation of chlorophyll biosynthesis in Chenopodium quinoa.

Protochlorophyllide oxidoreductase (POR) plays a key role in catalyzing the light-dependent reduction of protochlorophyllide (Pchlide) to chlorophyllide (Chlide), and thus promotes the transit from etiolated seedlings to green plants. In this study, by exploring ethyl methanesulfonate (EMS)-mediated mutagenesis in Chenopodium quinoa NL-6 variety, we identified a mutant nl6-35 that displays faded green leaf and reduced chlorophyll (Chl) and carotenoid contents. Bulk segregant analysis (BSA) revealed that a mutation in CqPORB gene is genetically associated with the faded green leaf of the nl6-35 mutant. Further study indicates that the nl6-35 mutant exhibits abnormal grana stacks and compromised conversion of Pchlide to Chlide upon illumination, suggesting the important role of CqPORB in producing photoactive Pchlide. Totally three CqPOR isoforms, including CqPORA, CqPORA-like, and CqPORB are identified in NL-6 variety. Transcriptional analysis shows that the expression of all these three CqPOR isoforms is regulated in light- and development-dependent manners, and in mature quinoa plants only CqPORB isoform is predominantly expressed. Subcellular localization analysis indicates that CqPORB is exclusively localized in chloroplast. Together, our study elucidates the important role of CqPORB in the regulation of Chl biosynthesis and chloroplast development in quinoa.

Light regulates chlorophyll biosynthesis via ELIP1 during the storage of Chinese cabbage

Chlorophyll loss is a major problem during green vegetable storage. However, the molecular mechanism is still unclear. In this study, a 21 days of storage experiments showed chlorophyll content was higher in light-stored Chinese cabbage (Brassica chinensis L.) leaves than those in dark-stored samples. Transcriptome analyses were performed on these samples to determine the effects of light. Among 311 differentially expressed genes (DEGs), early light-induced protein 1 (ELIP1) was identified as the main control gene for chlorophyll synthesis. Tissues and subcellular localization indicated that ELIP1 was localized in the nucleus. Motifs structure analyses, chromatin immunoprecipitation (ChIP) assays, luciferase reporter assays, and overexpression experiments demonstrated that ELIP1 regulated the expressions of genomes uncoupled 4 (GUN4), Glutamyl-tRNA reductase family protein (HEMA1), and Mg-protoporphyrin IX methyltransferase (CHLM) by binding to G-box-like motifs and affected chlorophyll biosynthesis during the storage of Chinese cabbage. It is a possible common tetrapyrrole biosynthetic pathway for chlorophylls, hemes, and bilin pigments in photosynthetic organisms. Our research also revealed that white light can be used as a regulatory factor to improve the storage ability and extent shelf life of Chinese cabbage.

Genome-Wide Investigation of the PtrCHLP Family Reveals That PtrCHLP3 Actively Mediates Poplar Growth and Development by Regulating Photosynthesis

Chlorophyll (Chl) plays a crucial role in plant photosynthesis. The geranylgeraniol reductase gene (CHLP) participates in the terminal hydrogenation of chlorophyll biosynthesis. Although there are many studies related to the genome-wide analysis of Populus trichocarpa, little research has been conducted on CHLP family genes, especially those concerning growth and photosynthesis. In this study, three CHLP genes were identified in Populus. The evolutionary tree indicated that the CHLP family genes were divided into six groups. Moreover, one pair of genes was derived from segmental duplications in Populus. Many elements related to growth were detected by cis-acting element analysis of the promoters of diverse PtrCHLPs. Furthermore, PtrCHLPs exhibit different tissue expression patterns. In addition, PtrCHLP3 is preferentially expressed in the leaves and plays an important role in regulating chlorophyll biosynthesis. Silencing of PtrCHLP3 in poplar resulted in a decrease in chlorophyll synthesis in plants, thus blocking electron transport during photosynthesis. Furthermore, inhibition of PtrCHLP3 expression in poplar can inhibit plant growth through the downregulation of photosynthesis. Ultimately, PtrCHLP3 formed a co-expression network with photosynthesis and chlorophyll biosynthesis-related genes, which synergistically affected the growth and photosynthesis of poplars. Thus, this study provides genetic resources for the improved breeding of fast-growing tree traits.

A foliar pigment-based bioassay for interrogating chloroplast signalling revealed that carotenoid isomerisation regulates chlorophyll abundance

BackgroundSome plastid-derived metabolites can control nuclear gene expression, chloroplast biogenesis, and chlorophyll biosynthesis. For example, norflurazon (NFZ) induced inhibition of carotenoid biosynthesis in leaves elicits a protoporphyrin IX (Mg-ProtoIX) retrograde signal that controls chlorophyll biosynthesis and chloroplast development. Carotenoid cleavage products, known as apocarotenoids, also regulate plastid development. The key steps in carotenoid biosynthesis or catabolism that can regulate chlorophyll biosynthesis in leaf tissues remain unclear. Here, we established a foliar pigment-based bioassay using Arabidopsis rosette leaves to investigate plastid signalling processes in young expanding leaves comprising rapidly dividing and expanding cells containing active chloroplast biogenesis.ResultsWe demonstrate that environmental treatments (extended darkness and cold exposure) as well as chemical (norflurazon; NFZ) inhibition of carotenoid biosynthesis, reduce chlorophyll levels in young, but not older leaves of Arabidopsis. Mutants with disrupted xanthophyll accumulation, apocarotenoid phytohormone biosynthesis (abscisic acid and strigolactone), or enzymatic carotenoid cleavage, did not alter chlorophyll levels in young or old leaves. However, perturbations in acyclic cis-carotene biosynthesis revealed that disruption of CAROTENOID ISOMERASE (CRTISO), but not ZETA-CAROTENE ISOMERASE (Z-ISO) activity, reduced chlorophyll levels in young leaves of Arabidopsis plants. NFZ-induced inhibition of PHYTOENE DESATURASE (PDS) activity caused higher phytoene accumulation in younger crtiso leaves compared to WT indicating a continued substrate supply from the methylerythritol 4-phosphate (MEP) pathway.ConclusionThe Arabidopsis foliar pigment-based bioassay can be used to differentiate signalling events elicited by environmental change, chemical treatment, and/or genetic perturbation, and determine how they control chloroplast biogenesis and chlorophyll biosynthesis. Genetic perturbations that impaired xanthophyll biosynthesis and/or carotenoid catabolism did not affect chlorophyll biosynthesis. The lack of CAROTENOID ISOMERISATION reduced chlorophyll accumulation, but not phytoene biosynthesis in young leaves of Arabidopsis plants growing under a long photoperiod. Findings generated using the newly customised foliar pigment-based bioassay implicate that carotenoid isomerase activity and NFZ-induced inhibition of PDS activity elicit different signalling pathways to control chlorophyll homeostasis in young leaves of Arabidopsis.

Proteomic analysis of a plastid gene encoding RPS4 mutant in Chinese cabbage (Brassica campestris L. ssp. pekinensis).

Plastids are important plant cell organelles containing a genome and bacterial-type 70S ribosomes-primarily composed of plastid ribosomal proteins and ribosomal RNAs. In this study, a chlorophyll-deficient mutant (cdm) obtained from double-haploid Chinese cabbage 'FT' was identified as a plastome mutant with an A-to-C base substitution in the plastid gene encoding the ribosomal protein RPS4. To further elucidate the function and regulatory mechanisms of RPS4, a comparative proteomic analysis was conducted between cdm and its wild-type 'FT' plants by isobaric tags and a relative and absolute quantitation (iTRAQ)-based strategy. A total of 6,245 proteins were identified, 540 of which were differentially abundant proteins (DAPs) in the leaves of cdm as compared to those of 'FT'-including 233 upregulated and 307 downregulated proteins. Upregulated DAPs were mainly involved in translation, organonitrogen compound biosynthetic process, ribosomes, and spliceosomes. Meanwhile, downregulated DAPs were mainly involved in photosynthesis, photosynthetic reaction centres, photosynthetic light harvesting, carbon fixation, and chlorophyll binding. These results indicated an important role of RPS4 in the regulation of growth and development of Chinese cabbage, possibly by regulating plastid translation activity by affecting the expression of specific photosynthesis- and cold stress-related proteins. Moreover, a multiple reaction monitoring (MRM) test and quantitative real-time polymerase chain reaction analysis confirmed our iTRAQ results. Quantitative proteomic analysis allowed us to confirm diverse changes in the metabolic pathways between cdm and 'FT' plants. This work provides new insights into the regulation of chlorophyll biosynthesis and photosynthesis in Chinese cabbage.

English

Magnesium protoporphyrin IX methyltransferase (ChlM) plays an important role in the regulation of chlorophyll biosynthesis and chloroplast development. In the present study, we isolated a ChlM gene, designated ClChlM, from Cymbidium [Cymbidium longibracteatum (Wu & Chen) Chen & Liu]. The open reading frame (ORF) sequence of ClChlM was 945 bp and encoded a putative protein of 314 amino acids. The deduced ClChlM contained the conserved SAM/SAH binding pocket and substrate binding sites. Subcellular localization analysis of ClChlM revealed that the protein was localized in the chloroplast. Ectopic overexpression of ClChlM in tobacco (Nicotiana benthamiana Domin) increased ALA-synthesizing capacity and chlorophyll content and widely upregulated the expression level of photosynthesis-related genes, such as ClHemA, ClGSA, ClLhcb, ClCHLI, and ClCHLH. In conclusion, these results demonstrate that ClChlM plays a crucial role in the regulation of chlorophyll biosynthesis in C. longibracteatum and will help in breeding for leaf colour variance in the future. © 2021 Friends Science Publishers

Characterization and Fine Mapping of a Yellow-Virescent Gene Regulating Chlorophyll Biosynthesis and Early Stage Chloroplast Development in Brassica napus

Chlorophyll biosynthesis and chloroplast development are crucial to photosynthesis and plant growth, but their regulatory mechanism remains elusive in many crop species. We isolated a Brassica napus yellow-virescent leaf (yvl) mutant, which exhibited yellow-younger-leaf and virescent-older-leaf with decreased chlorophyll accumulation and delayed chloroplast development. We mapped yvl locus to a 70-kb interval between molecular markers yvl-O10 and InDel-O6 on chromosome A03 in BC2F2 population using whole genome re-sequencing and bulked segregant analysis. The mutant had a ‘C’ to ‘T’ substitution in the coding sequence of BnaA03.CHLH, which encodes putative H subunit of Mg-protoporphyrin IX chelatase (CHLH). The mutation resulted in an imperfect protein structure and reduced activity of CHLH. It also hampered the plastid encoded RNA polymerase which transcribes regulatory genes of photosystem II and I. Consequently, the chlorophyll a/b and carotenoid contents were reduced and the chloroplast ultrastructure was degraded in yvl mutant. These results explain that a single nucleotide mutation in BnaA03.CHLH impairs PEP activity to disrupt chloroplast development and chlorophyll biosynthesis in B. napus.

A GATA Transcription Factor from Soybean (Glycine max) Regulates Chlorophyll Biosynthesis and Suppresses Growth in the Transgenic Arabidopsis thaliana.

Chlorophyll plays an essential role in photosynthetic light harvesting and energy transduction in green tissues of higher plants and is closely related to photosynthesis and crop yield. Identification of transcription factors (TFs) involved in regulating chlorophyll biosynthesis is still limited in soybean (Glycine max), and the previously identified GmGATA58 is suggested to potentially modulate chlorophyll and nitrogen metabolisms, but its complete function is still unknown. In this study, subcellular localization assay showed that GmGATA58 was localized in the nucleus. Histochemical GUS assay and qPCR assay indicated that GmGATA58 was mainly expressed in leaves and responded to nitrogen, light and phytohormone treatments. Overexpression of GmGATA58 in the Arabidopsis thaliana ortholog AtGATA21 (gnc) mutant complemented the greening defect, while overexpression in Arabidopsis wild-type led to increasing chlorophyll content in leaves through up-regulating the expression levels of the large of chlorophyll biosynthetic pathway genes, but suppressing plant growth and yield, although the net photosynthetic rate was slightly improved. Dual-luciferase reporter assay also supported that GmGATA58 activated the transcription activities of three promoters of key chlorophyll biosynthetic genes of soybean in transformed protoplast of Arabidopsis. It is concluded that GmGATA58 played an important role in regulating chlorophyll biosynthesis, but suppressed plant growth and yield in transgenic Arabidopsis.

A Thylakoid Membrane Protein Functions Synergistically with GUN5 in Chlorophyll Biosynthesis

Chlorophyll (Chl) is essential for photosynthetic reactions and chloroplast development. While the enzymatic pathway for Chl biosynthesis is well established, the regulatory mechanism underlying the homeostasis of Chl levels remains largely unknown. In this study, we identified CBD1 (Chlorophyll Biosynthetic Defect1), which functions in the regulation of chlorophyll biosynthesis. The CBD1 gene was expressed specifically in green tissues and its protein product was embedded in the thylakoid membrane. Furthermore, CBD1 was precisely co-expressed and functionally correlated with GUN5 (Genome Uncoupled 5). Analysis of chlorophyll metabolic intermediates indicated that cbd1 and cbd1gun5 mutants over-accumulated magnesium protoporphyrin IX (Mg-Proto IX). In addition, the cbd1 mutant thylakoid contained less Mg than the wild type not only as a result of lower Chl content, but also implicating CBD1 in Mg transport. This was supported by the finding that CBD1 complemented a Mg2+ uptake-deficient Salmonella strain under low Mg conditions. Taken together, these results indicate that CBD1 functions synergistically with CHLH/GUN5 in Mg-Proto IX processing, and may serve as a Mg-transport protein to maintain Mg homeostasis in the chloroplast.

The miR396-GRFs Module Mediates the Prevention of Photo-oxidative Damage by Brassinosteroids during Seedling De-Etiolation in Arabidopsis.

The switch from dark- to light-mediated development is critical for the survival and growth of seedlings, but the underlying regulatory mechanisms are incomplete. Here, we show that the steroids phytohormone brassinosteroids play crucial roles during this developmental transition by regulating chlorophyll biosynthesis to promote greening of etiolated seedlings upon light exposure. Etiolated seedlings of the brassinosteroids-deficient det2-1 (de-etiolated2) mutant accumulated excess protochlorophyllide, resulting in photo-oxidative damage upon exposure to light. Conversely, the gain-of-function mutant bzr1-1D (brassinazole-resistant 1-1D) suppressed the protochlorophyllide accumulation of det2-1, thereby promoting greening of etiolated seedlings. Genetic analysis indicated that phytochrome-interacting factors (PIFs) were required for BZR1-mediated seedling greening. Furthermore, we reveal that GROWTH REGULATING FACTOR 7 (GRF7) and GRF8 are induced by BZR1 and PIF4 to repress chlorophyll biosynthesis and promote seedling greening. Suppression of GRFs function by overexpressing microRNA396a caused an accumulation of protochlorophyllide in the dark and severe photobleaching upon light exposure. Additionally, BZR1, PIF4, and GRF7 interact with each other and precisely regulate the expression of chlorophyll biosynthetic genes. Our findings reveal an essential role for BRs in promoting seedling development and survival during the initial emergence of seedlings from subterranean darkness into sunlight.

From Chloroplast Biogenesis to Chlorophyll Accumulation: The Interplay of Light and Hormones on Gene Expression in Camellia sinensis cv. Shuchazao Leaves.

Chloroplast development and chlorophyll metabolism have been well described in model plants but not in perennial woody crops. Of particular interest is the interplay between light and hormones under shade conditions. We report that the shade induced accumulation of chlorophylls in Camellia sinensis cv. Shuchazao leaves is at least as a result of (a) positive changes in chloroplast development and (b) light/hormonal regulation of genes and transcription factors involved in the chlorophyll biosynthesis pathway. Under shade conditions, leaves developed an abundance of enlarged chloroplasts encapsulating more prominent thylakoid membranes. Four major metabolites in the chlorophyll biosynthesis pathway namely Chl a, Chl b, DPP, and Mg-Proto IX increased under shade conditions while PBG decreased significantly. Significant changes were found at the transcription level of regulators of chloroplast biogenesis (GLK1 and LHCB), the structural genes in the chlorophyll biosynthesis pathway (HEMA1, CLH1, PORA, and CAO) and potential components involved in light signaling (PHYA, CRY1, HY5, and DELLAs). Two central signal integrators (GLK1 and LHCB) between the nucleus and chloroplast showed clear responses to shade, suggesting a crucial role of light in regulating chloroplast development in tea leaves. Concurrent with the changes in gene expression, the concentrations of endogenous phytohormones (auxin, cytokinin, and gibberellins) increased significantly in the later stages of shade conditions. Two key integrators involved in the hormone signal pathways, EIN3 and EBF1/2, increased under shade conditions suggesting that shade induced changes to hormone levels may play some role in modulating chlorophyll biosynthesis in the tea leaves. Overall, this data suggests that the light and hormone influence over chloroplast development and chlorophyll biosynthesis in Camellia is similar to that of Arabidopsis. This study provides new insights into the molecular mechanisms that regulate chlorophyll biosynthesis in response to light and hormones in a commercially important woody plant such as Camellia, which may facilitate the breeding of high-chlorophyll tea cultivars for the improvement of sensory features of the green tea product.

Isolation and Identification of a TaTDR-Like Wheat Gene Encoding a bHLH Domain Protein, Which Negatively Regulates Chlorophyll Biosynthesis in Arabidopsis

Chlorophyll biosynthesis plays a vital role in chloroplast development and photosynthesis in plants. In this study, we identified an orthologue of the rice gene TDR (Oryza sativa L., Tapetum Degeneration Retardation) in wheat (Triticum aestivum L.) called TaTDR-Like (TaTDRL) by sequence comparison. TaTDRL encodes a putative 557 amino acid protein with a basic helix-loop-helix (bHLH) conserved domain at the C-terminal (295–344 aa). The TaTDRL protein localised to the nucleus and displayed transcriptional activation activity in a yeast hybrid system. TaTDRL was expressed in the leaf tissue and expression was induced by dark treatment. Here, we revealed the potential function of TaTDRL gene in wheat by utilizing transgenic Arabidopsis plants TaTDRL overexpressing (TaTDRL-OE) and TaTDRL-EAR (EAR-motif, a repression domain of only 12 amino acids). Compared with wild-type plants (WT), both TaTDRL-OE and TaTDRL-EAR were characterized by a deficiency of chlorophyll. Moreover, the expression level of the chlorophyll-related gene AtPORC (NADPH:protochlorophyllide oxidoreductase C) in TaTDRL-OE and TaTDRL-EAR was lower than that of WT. We found that TaTDRL physically interacts with wheat Phytochrome Interacting Factor 1 (PIF1) and Arabadopsis PIF1, suggesting that TaTDRL regulates light signaling during dark or light treatment. In summary, TaTDRL may respond to dark or light treatment and negatively regulate chlorophyll biosynthesis by interacting with AtPIF1 in transgenic Arabidopsis.