Fine Mapping and Transcriptome Analysis of Virescent Leaf Gene v-2 in Cucumber (Cucumis sativus L.).

Kaijing Zhang,Ji Li,Yifan Wei,Ying Li,Martin Kagiki Njogu,Jinfeng Chen,Qunfeng Lou,Wenwei Zhu

doi:10.3389/fpls.2020.570817

Abstract

Leaf color mutants are the ideal materials to explore the pathways of chlorophyll metabolism, chloroplast development and photosynthesis system. In this study, a new virescent leaf mutant 104Y was identified by spontaneous mutation, whose cotyledon and upper five true leaves were yellow color. The yellow true leaves gradually turned green from top to bottom with increased chlorophyll contents. Genetic analysis indicated that the virescent leaf was controlled by one single recessive gene v-2, which was accurately mapped into 36.0–39.7 Mb interval on chromosome 3 by using BSA-seq and linkage analysis. Fine mapping analysis further narrowed v-2 into 73-kb genomic region including eight genes with BC1 and F2 populations. Through BSA-seq and cDNA sequencing analysis, only one nonsynonymous mutation existed in the Csa3G890020 gene encoding auxin F-box protein was identified, which was predicted as the candidate gene controlling virescent leaf. Comparative transcriptome analysis and quantitative real-time PCR analysis revealed that the expression level of Csa3G890020 was not changed between EC1 and 104Y. However, RNA-seq analysis identified that the key genes involved in chlorophyll biosynthesis and auxin signaling transduction network were mainly down-regulated in 104Y compared with EC1, which indicated that the regulatory functions of Csa3G890020 could be performed at post-transcriptional level rather than transcriptional level. This is the first report to map-based clone an auxin F-box protein gene related to virescent leaf in cucumber. The results will exhibit a new insight into the chlorophyll biosynthesis regulated by auxin signaling transduction network.

Highlights

In higher plants, leaf color variation occurs commonly at different stages of growth, which is usually caused by the mutations of some critical genes related to the chloroplast development, chlorophyll biosynthesis and plant photosynthesis (Mao et al, 2019)
The virescent mutant 104Y was identified by natural mutation
The cotyledon of 104Y was yellow color when seedlings firstly emerged from the soil (Figure 1A) and gradually turned green following the true leaves grow up

Summary

Introduction

Leaf color variation occurs commonly at different stages of growth, which is usually caused by the mutations of some critical genes related to the chloroplast development, chlorophyll biosynthesis and plant photosynthesis (Mao et al, 2019). Except for the chloroplast development, chlorophyll biosynthesis and photosynthesis pathway, many hormones are involved in light-induced seedling greening. Kobayashi et al (2017) reported that chlorophyll synthesis genes are markedly activated in detached roots via cytokinin but are repressed by auxin, suggesting that auxin signaling is involved in the regulation of chlorophyll biosynthesis in the root greening response. Ethylene could dramatically represses Pchlide accumulation and induces the gene expressions of both PORA and PORB in etiolated seedlings, affecting chlorophyll biosynthesis (Zhong et al, 2009; Zhong et al, 2010; Zhong et al, 2014)

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Results

Conclusion