A valine residue deletion in ZmSig2A, a sigma factor, accounts for a revertible leaf-color mutation in maize

ChuanLi^a1, Jingwen Wanga¹, Zhaoyong Hu^a, Yuanyan Xia^a, QiangHuang^a, TaoYu^a, Hongyang Yi^a, Yanli Lu^ab, JingWang^a, Moju Cao^ab.

^aMaize Research Institute, Sichuan Agricultural University, Chengdu 611130, Sichuan, China

^bState Key Laboratory of Crop Gene Exploration and Utilization in Southwest China, Chengdu 611130, Sichuan, China

doi.org/10.1016/j.cj.2021.01.005

Abstract

A nuclear-encoded sigma (σ) factor is essential for the transcriptional regulation of plant chloroplast-encoded genes. Five putative maize σ factors have been identified by database searches, but their functions are unknown. We report a maize leaf color mutantetiolated/albino leaf 1(eal1) that was derived from space mutation breeding. Theeal1mutant displays etiolated or albino leaves that then gradually turn to normal green at the seedling stage. The changes ineal1leaf color are associated with changes in photosynthetic pigment content and chloroplast development. Map-based cloning revealed that a single amino-acid deletion changing Val₄₈₀-Val₄₈₁-Val₄₈₂to Val₄₈₀-Val₄₈₁, in the C-terminal domain σ₄of the putative σ factorZmSig2A, is responsible for theeal1mutation. In comparison with the expression level of the wild-type (WT) alleleZmSig2A⁺in WT plants, much higher expression of the mutant alleleZmSig2A^ΔVineal1plants was detected before theeal1plants turned to normal green. ZmSig2A shows the highest similarity to rice OsSig2A andArabidopsisSIG2. Ectopic expression ofZmSig2A⁺orZmSig2A^ΔVdriven by the cauliflower mosaic virus 35S promoter rescued the pale green leaf of thesig2mutant, but ectopic expression ofZmSig2A^ΔVdriven by theSIG2promoter did not. We propose that the Val deletion generated a new weak allele ofZmSig2Athat cannot completely abolish the ZmSig2A function. Some genes involved in chloroplast development and photosynthesis-associated nuclear genes showed significant expression differences betweeneal1and WT plants. We conclude thatZmSig2Aencoding a σ factor is essential for maize chloroplast development. Theeal1mutant with a weak allele ofZmSig2Arepresents a valuable genetic resource for investigating the regulation of ZmSig2A-mediated chloroplast development in maize. Theeal1mutation may be useful as a marker for early identification and elimination of false hybrids or transgene transmission in the application of genetic male sterility to commercial hybrid seed production.

Keywords

Leaf color mutant; Map-based cloning; Sigma factor; Chloroplast development; Maize