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

Huiyu Wu,Yi Feng,Narong Shi,Hongfei Fu,Daojie Sun,Cong Liu,Lingli Zhang,Xuyao An,Li Cao

doi:10.3390/ijms19061594

Abstract

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.

Highlights

Photosynthesis is the basis of plant production, and at least 90% of grain yield is determined by photosynthesis [1]
Mg-chelatase (EC 6.6.1.1) is a key regulatory enzyme that catalyzes the insertion of Mg2+ into protoporphyrin IX (Proto IX) in an ATP-dependent manner as the first committed step in Chl biosynthesis, where this protein complex comprises magnesium chelatase subunit I (CHLI), D (CHLD), and H (CHLH) in higher plants [16], which are all required for its activity [17]
To understand the molecular basis of leaf color polymorphism in the progeny of the yellow-green leaf color mutant (Ygm) mutant, cDNA libraries were constructed from the half-developed leaves of the Y and G types based on three biological replicates, which were sequenced using the Illumina HiSeqTM 2500 platform (Illumina, San Diego, CA, USA)

Summary

Introduction

Photosynthesis is the basis of plant production, and at least 90% of grain yield is determined by photosynthesis [1]. Mg-chelatase (EC 6.6.1.1) is a key regulatory enzyme that catalyzes the insertion of Mg2+ into protoporphyrin IX (Proto IX) in an ATP-dependent manner as the first committed step in Chl biosynthesis, where this protein complex comprises magnesium chelatase subunit I (CHLI), D (CHLD), and H (CHLH) in higher plants [16], which are all required for its activity [17]. In peas, the virus-induced gene silencing of CHLI and CHLD yields plants with yellow leaf phenotypes and reduced Mg-chelatase activities, as well as lower Chl accumulation correlated with undeveloped thylakoid membranes [22]. The chl and chl genes encode the CHLD and CHLI subunits of Mg-chelatase, and their mutation leads to underdeveloped chloroplasts and low Chl contents [13]. To the best of our knowledge, only a few CHLD, CHLH, and CHLI genes encoding the Mg-chelatase D, H, and I subunits have been reported in wheat leaf color mutants [27,28,29]

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Results

Discussion

Conclusion