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A new demethylase gene OsDML4 involved in high temperature increased grain chalkiness in rice (Oryza sativa L.).

High temperature (HT) can affect the accumulation of seed storage materials and cause adverse effects on the yield and quality of rice. DNA methylation plays an important role in plant growth and development. Here, we identified a new demethylase gene OsDML4 and discovered its function on cytosine demethylation to affect the endosperm formation. Loss function of OsDML4 induced chalky endosperm only under HT and dramatically reduced the transcription and accumulation of glutelins and 16-kDa prolamin. The expression of two transcription factors RISBZ1 and RPBF was significantly declined in the osdml4 mutants, which caused adverse effects on the formation of protein bodies (PBs) with greatly decreased PB-II number, incomplete and abnormally shaped PB-II. Whole-genome bisulfite sequencing analysis of seeds at 15 days after pollination revealed much higher global methylation levels of CG, CHG and CHH contexts in the osdml4 mutants compared to wild type. Moreover, the RISBZ1 promoter was hypermethylated but RPBF promoter was nearly unchanged under HT. No significant difference was detected between WT and osdml4 mutants under normal temperature. Our study demonstrated a novel OsDML4-mediated DNA methylation involving in the formation of chalky endosperm only under HT and provided a new perspective in regulating endosperm development and the accumulation of SSPs in rice.