Rice Chalky Grain 5 regulates natural variation for grain quality under heat stress

Abstract

Heat stress occurring during rice (Oryza sativa) grain development reduces grain quality, which often manifests as increased grain chalkiness. Although the impact of heat stress on grain yield is well-studied, the genetic basis of rice grain quality under heat stress is less explored as quantifying grain quality is less tractable than grain yield. To address this, we used an image-based colorimetric assay (Red, R; and Green, G) for genome-wide association analysis to identify genetic loci underlying the phenotypic variation in rice grains exposed to heat stress. We found the R to G pixel ratio (RG) derived from mature grain images to be effective in distinguishing chalky grains from translucent grains derived from control (28/24°C) and heat stressed (36/32°C) plants. Our analysis yielded a novel gene, rice Chalky Grain 5 (OsCG5) that regulates natural variation for grain chalkiness under heat stress. OsCG5 encodes a grain-specific, expressed protein of unknown function. Accessions with lower transcript abundance of OsCG5 exhibit higher chalkiness, which correlates with higher RG values under stress. These findings are supported by increased chalkiness of OsCG5 knock-out (KO) mutants relative to wildtype (WT) under heat stress. Grains from plants overexpressing OsCG5 are less chalky than KOs but comparable to WT under heat stress. Compared to WT and OE, KO mutants exhibit greater heat sensitivity for grain size and weight relative to controls. Collectively, these results show that the natural variation at OsCG5 may contribute towards rice grain quality under heat stress.

Targeted mutagenesis of the vacuolar H+ translocating pyrophosphatase gene reduces grain chalkiness in rice

“…On the other hand, numerous QTLs have been reported that control chalkiness (Dwiningsih et al., 2021; Edwards et al., 2017; Gao et al., 2016; Guo et al., 2011; He et al., 1999; Kobayashi et al., 2013; Tabata et al., 2007; Tan et al., 2000; Wan et al., 2005; Zhao et al., 2016). However, only a few causative genes have been identified (Chandran et al., 2022; Li et al., 2014), one of which is Chalk5 , as identified in a population derived from the biparental cross between two indica rice varieties differing in grain chalk content. Chalk5 encodes one of the vacuolar H + translocating pyrophosphatases ( V‐PPase ).…”

FLOURY ENDOSPERM24, a heat shock protein 101 (HSP101), is required for starch biosynthesis and endosperm development in rice

“…Under normal temperature conditions, starch is efficiently synthesized and densely packed, forming polyhedral starch granules and mature translucent grains (Matsushima et al, 2010). By contrast, high temperature at the early filling stage significantly interferes with starch biosynthesis and leads to the formation of floury or chalky endosperm filled with round and irregularly arranged starch granules (Tashiro & Wardlaw, 1991;Hakata et al, 2012;Morita et al, 2016;Zhang et al, 2018;Xu et al, 2020;Paul et al, 2020;Ren et al, 2021;Cao et al, 2022;Chandran et al, 2022). Several key regulatory factors that are required for starch biosynthesis in endosperm under heat stress have been reported in rice.…”

Response of Photosynthesis in Wheat (Triticum aestivum L.) Cultivars to Moderate Heat Stress at Meiosis and Anthesis Stages

“…To mitigate and adapt the consequence of climate change on wheat production, scientists are working on developing heat-tolerant wheat germplasm resources. In order to adapt new crop varieties to future climates, we need to get information on how crops cope with high temperatures and how to improve their heat tolerance [10,11]. Photosynthesis, as the ultimate source of energy for crop yield formation, and photosynthesis in wheat leaves during the meiosis and anthesis stages directly affects wheat grain weight, which is a fundamental factor in determining wheat yield [12].…”