Abstract
BackgroundLeaf color mutants are the ideal materials to explore the pathways of chlorophyll (Chl) metabolism, chloroplast development, and photosynthesis system. In this study, a spontaneous yellow-green leaf wucai (Brassica campestris L.) mutant “WY16–13” was identified, which exhibited yellow-green leaf color during its entire growth period. However, current understanding of the molecular mechanism underlying Chl metabolism and chloroplast development of “WY16–13” is limited.ResultsTotal Chl and carotenoid content in WY16–13 was reduced by 60.92 and 58.82%, respectively, as compared with its wild type parental line W16–13. Electron microscopic investigation revealed fewer chloroplasts per cell and looser stroma lamellae in WY16–13 than in W16–13. A comparative transcriptome profiling was performed using leaves from the yellow-green leaf type (WY16–13) and normal green-leaf type (W16–13). A total of 54.12 million (M) (WY16–13) and 56.17 M (W16–13) reads were generated. A total of 40,578 genes were identified from the mapped libraries. We identified 3882 differentially expressed genes (DEGs) in WY16–13 compared with W16–13 (i.e., 1603 upregulated genes and 2279 downregulated genes). According to the Gene Ontology (GO) term and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses, these DEGs are involved in porphyrin and Chl metabolism [i.e., chlorophyllase (CLH), heme oxygenase (HO), chlorophyll (ide) b reductase (NYC), and protochlorophyllide oxidoreductase (POR) genes], carbohydrate metabolism, photosynthesis, and carbon fixation in photosynthetic organisms. Moreover, deficiency in Chl biosynthetic intermediates in WY16–13 revealed that the formation of the yellow-green phenotype was related to the disorder of heme metabolism.ConclusionsOur results provide valuable insights into Chl deficiency in the yellow-green leaf mutant and a bioinformatics resource for further functional identification of key allelic genes responsible for differences in Chl content.
Highlights
Leaf color mutants are the ideal materials to explore the pathways of chlorophyll (Chl) metabolism, chloroplast development, and photosynthesis system
Based on a combination of physiological and bioinformatics analyses, we identified differentially expressed genes (DEGs) related to Chl biosynthesis, and transcript levels of some key genes were evaluated to validate their involvement in leaf coloration
The results show that the Glutamate (Glu), 5-aminolevulinic acid (ALA), porphobilinogen (PBG), uroporphyrinogen Coproporphyrinogen III (III) (Urogen III), coproporphyrinogen III (Coprogen III), Mg-protoporphyrin IX (Mg-Proto IX), protoporphyrin IX (Proto IX), and protochlorophyllide (Pchlide) contents of the leaves of WY16–13 plants were significantly lower than those of W16–13 plants
Summary
Leaf color mutants are the ideal materials to explore the pathways of chlorophyll (Chl) metabolism, chloroplast development, and photosynthesis system. A yellow-green leaf phenotype is attributed to the disruption of the Chl synthase-encoding gene YGL1 or impaired chlorophyllide esterification, which results in lower Chl content and delayed chloroplast development [11, 12]. The pale-green leaf mutant pgl that is deficient in protochlorophyllide oxidoreductase (PORB) results in lower photosynthetic pigment content and grana lamellae in thylakoid compared to the wild-type [14]. Both external and internal factors could influence Chl content such as light, salt, and osmotic stress due to alterations in gene expression or post-translational modification of proteins involved in Chl metabolism [15,16,17]. Snowy cotyledon 3 (SCO3) localizes to peroxisomes, and its mutation in Arabidopsis leads to loss of Chl content and defective chloroplast function [19]
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