Metabolomic analysis reveals metabolites and pathways involved in grain quality traits of high-quality rice cultivars under a dry cultivation system

Dry cultivation of high-yielding or drought-resistant rice cultivars relieves the current pressure on rice cultivation systems. However, the metabolites and metabolic pathways that affect rice quality in high-yield or drought-resistant rice cultivars under dry cultivation have not yet been explored. A field experiment was conducted in 2017 to explore the effects of flooding irrigation (F) and dry cultivation (D) of high-yield and -quality cultivars (Huanghuazhan, HH; Yueyou9113, YY) and a drought-resistant cultivar (Hanyou73, HY) on rice quality traits using metabolomic analysis. Treatment DHH maintained higher head rice yield, amylose content, protein content, and breakdown values and a lower whiteness index and setback value than other cultivars under dry cultivation. These rice quality traits were related to 16 metabolites and 8 metabolic pathways. DHH showed decreases in stress response metabolites (m72, m98, m127, m165, m167, m213, m297, and m298) but maintained stress resistance (m29, m30, m39, m48, and m58) and sucrose (m150) accumulation in grains to support head rice yields and a low whiteness index. Raising the lactose, choline, and nicotinoylcholine levels in rice grains improved their protein content and cooking quality. DHH also adjusted the glycine, serine and threonine metabolism, galactose metabolism, and starch and sucrose metabolism of rice. This affected the biosynthesis of anthocyanin, phenylpropanoid, and flavonoid, supporting protein biosynthesis and starch accumulation in the endosperm. These findings provide further possibilities for improving rice quality traits of high-yield and -quality rice cultivars under dry cultivation.