Functional Divergence of G and Its Homologous Genes for Green Pigmentation in Soybean Seeds.

Yusuke Tokumitsu,Ayaka Hase,Haruna Nakano,Hiroshi Yamatani,Akito Kaga,Taiken Nakashima,Takuto Kozu,Yoshitake Takada,Makoto Kusaba,Tetsuya Yamada,Masao Ishimoto,Jun Abe,Hiroki Sasada,Takeshi Ito

doi:10.3389/fpls.2021.796981

Abstract

The degradation of chlorophyll in mature soybean seeds is closely related to the development of their yellow color. In this study, we examined G, its homologue G-like (GL), and their mutant alleles and investigated the relationship between these genes and chlorophyll accumulation in the seed coats of mature seeds. Transient expression of G and GL proteins fused with green fluorescent protein revealed that both were localized in plastids. Overexpression of G resulted in the accumulation of chlorophyll in the seed coats and cotyledons of mature seeds, indicating that high expression levels of G result in chlorophyll accumulation that exceeds its metabolism in the seeds of yellow soybean. Analysis of near isogenic lines at the G locus demonstrated a significant difference in the chlorophyll content of the seed coats and cotyledons of mature seeds when G and mutant g alleles were expressed in the d1d2 stay-green genetic background, indicating that the G protein might repress the SGR-independent degradation of chlorophyll. We examined the distribution of mutant alleles at the G and GL loci among cultivated and wild soybean germplasm. The g allele was widely distributed in cultivated soybean germplasm, except for green seed coat soybean lines, all of which contained the G allele. The gl alleles were much fewer in number than the g alleles and were mainly distributed in the genetic resources of cultivated soybean from Japan. None of the landraces and breeding lines investigated in this study were observed to contain both the g and gl alleles. Therefore, in conclusion, the mutation of the G locus alone is essential for establishing yellow soybeans, which are major current soybean breeding lines.

Highlights

IntroductionThe crop originated from its Chlorophyll Accumulation in Seed Coat wild relative G. soya, which is native to East Asia, and was domesticated in China approximately 3,000–5,000 years ago (Fukuda, 1933; Nagata, 1959; Hymowitz and Newell, 1981)
Soybean (Glycine max, 2n = 2x = 40) is one of the most economically important crops worldwide because its seeds contain high-quality proteins and have an amino acid score comparable to that of beef and egg white
The concentration of chlorophyll in the seed coat of the recombinant inbred lines (RILs) ranged from 0.00 to 25.18 mg/100 g dry weight (DW; Figure 2B), with TK780 and B01167 producing it at concentrations of 0.07 ± 0.05 and 19.3 ± 1.0 mg/100 g DW in their seed coats, respectively

Summary

Introduction

The crop originated from its Chlorophyll Accumulation in Seed Coat wild relative G. soya, which is native to East Asia, and was domesticated in China approximately 3,000–5,000 years ago (Fukuda, 1933; Nagata, 1959; Hymowitz and Newell, 1981). Elucidating the molecular mechanisms of crop domestication provides a thorough understanding of the crop’s evolution and valuable information about crop improvement and about the origins of agriculture (Jones and Brown, 2000). The molecular mechanisms of several domesticated traits in soybean have been elucidated, including environmental adaptability, lack of pod shattering, lack of hard seededness, increased seed size, and absence of vine growth habit (Liu et al, 2007; Dong et al, 2014; Sun et al, 2015; Wang et al, 2019)

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Conclusion