Novel Wx alleles induced by chemical mutagens in rice, Oryza sativa L.

Abstract

From mutant pools of two Taiwanese elite japonica cultivars, Tainung 67 and Taikeng 8, we identified 13 mutant lines possessing opaque endosperm with relatively low amylose contents (AC) ranging from 1.5% to 7.1%. Because of different AC, paste viscosities of these 13 mutant lines differed, as revealed by palatability and physicochemical properties. The mutated gene conferring opaque endosperm was isolated from the F2 population of one mutant line, WY1× indica cv. ‘Taichung Sen 17’, by positional cloning, revealing a G3018→A3018 substitution at exon 9 of Waxy leading to a non‐synonymous mutation from alanine to valine. Two additional alleles were identified from the other 12 mutant lines, for which single‐nucleotide substitutions G2708 → A2708 and G3029 → A3029 occurred in exons 8 and 9, leading to non‐synonymous mutations from arginine to histidine and glutamic acid to lysine, respectively. The three novel wx alleles had different effects on grain quality, specifically on eating and cooking quality, and could be applied in rice breeding programmes to develop new low AC varieties by marker‐assisted selection.

A rare Waxy allele coordinately improves rice eating and cooking quality and grain transparency

“…Wx has been modified by conventional mutagenesis and biotechnological methods such as RNA interference (RNAi) or gene editing by clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR‐associated nuclease Cas9 (Liu et al, 2003; Ma et al, 2015; Lin et al, 2017). For instance, the Wx mq and Wx mp alleles were generated by N‐methyl‐N‐nitrosourea‐induced mutagenesis (Sato et al, 2002; Yang et al, 2013).…”

“…For instance, the Wx mq and Wx mp alleles were generated by N‐methyl‐N‐nitrosourea‐induced mutagenesis (Sato et al, 2002; Yang et al, 2013). Another 13 Wx mutants were induced by treatment with sodium azide, yielding mutant grains with typically opaque endosperm and very low AC ranging from 1.5% to 7.1% (Lin et al, 2017). In terms of the modulation of GBSSI, our previous studies showed that GBSSI activity is very sensitive to amino acid changes (Liu et al, 2014; Zhang et al, 2017), and thus, it is very difficult to generate mutants with moderate AC by editing the Wx coding sequence directly.…”

Waxy allele diversification in foxtail millet (Setaria italica) landraces of Taiwan

“…The Wx of rice is the best-studied case. Some rice waxy alleles were chemically induced mutant, such as Wx mq and WY1 [22, 23]. However, several naturally occurring alleles in landraces Wx op , Wx hp , and Wx zm possessing low AC because of nonsynonymous substitutions, were identified and preserved in Yunnan landraces [20, 21, 52].…”

“…Alleles resulted from SNPs uncovered from landraces, e.g. Wx op , Wx mq , and Wx hp , or mutated accessions affected AC, grain appearance, and eating and cooking quality as consequence [20–23]. In barley, the level of GBBSI mRNA was greatly reduced by the deletion of the promoter and/or 5’UTR [24, 25].…”

Starch Components, Starch Properties and Appearance Quality of Opaque Kernels from Rice Mutants

“…The M160, M226, and M252 kernels were waxy and opaque, the other mutants had floury endosperms. It has been widely reported that the waxy rice kernels with ACs below 2% result from a deficiency of granule-bound starch synthase I and exhibit a typically waxy phenotype [40]. Recently, Zhang et al [41] reported that the waxy phenotype of a dry kernel is due to the cavities in the centre of starch granules.…”