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Amylose content controlled by Wx determines rice grain quality, which is easily affected by high temperature. Wxa and Wxb are the two typical Wx alleles in rice, however, their effects on quality formation in response to high temperature under the backgrounds of indica rice and japonica rice have not been systematically compared. In this study, the near-isogenic lines (NILs) of Wxa and Wxb with japonica rice 2661 and indica rice 3611 backgrounds were treated by high temperature during the grain-filling stages. High temperature accelerated the grain ripening process, decreased the thousand-kernel weight, and increased the chalkiness degree of all rice samples. However, these traits of Wx NILs with 3611 background were more susceptible to high temperature than those with 2661 background. Furthermore, high-temperature treatment decreased the amylose contents (AC) and starch viscosities but increased the gelatinization temperature of all the Wx NILs. The 3611-Wxa was atypical Wxa-type rice, whose AC was more sensitive to high temperature. The AC result was consistent with quantitative analysis of GBSSI by Western blot. In addition, the effects of Wx genotype and genetic background on rice physicochemical quality (such as the gel consistencies, starch crystallinity, and the morphological structure of starch grains) in response to high temperature were systematically analyzed. These results have important guiding significance for rice-quality improvement under high-temperature climate. [ABSTRACT FROM AUTHOR]

Rice starch regulator1 (RSR1) participates in the regulation of starch synthesis in rice, but it's function on starch synthesis and quality formation in response to high temperature is unknown. RSR1 mutation resulted in a significant increase in the abscisic acid (ABA) content in rice grains under both normal and high temperature, and the effect of high temperature on grain filling and quality formation of the rsr1 mutants was significantly reduced. The grain size, 1000-kernels weight, amylose content, gelatinization temperature, and starch viscosity of the rsr1 mutants were less sensitive to high temperature. Loss of RSR1 function increased the expression levels of starch synthesis-related genes and reduced their responses to high temperature to some extent. Besides, the percentage of germinated seeds from rsr1 mutants was significantly lower than that of the wild-type, and the difference was more significant under ABA treatment. The shoot lengths of the rsr1 mutants were remarkably shorter than those of the wild-type, which was further exacerbated by ABA treatment. These results indicated that loss function of RSR1 can improve rice quality performance at high temperature by moderately increasing the ABA content of rice grains, which provides theoretical significance for the cultivation of better-quality rice with high-temperature resistance. [ABSTRACT FROM AUTHOR]