Salinity stress is one of the most prominent abiotic stresses that negatively affect crop production. Transcription factors (TFs) are involved in the absorption, transport, or compartmentation of sodium (Na+) or potassium (K+) to resist salt stress. The basic helix–loop–helix (bHLH) is a TF gene family critical for plant growth and stress responses, including salinity. Herein, we used the CRISPR/Cas9 strategy to generate the gene editing mutant to investigate the role of OsbHLH024 in rice under salt stress. The A nucleotide base deletion was identified in the osbhlh024 mutant (A91). Exposure of the A91 under salt stress resulted in a significant increase in the shoot weight, the total chlorophyll content, and the chlorophyll fluorescence. Moreover, high antioxidant activities coincided with less reactive oxygen species (ROS) and stabilized levels of MDA in the A91. This better control of oxidative stress was accompanied by fewer Na+ but more K+, and a balanced level of Ca2+, Zn2+, and Mg2+ in the shoot and root of the A91, allowing it to withstand salt stress. Furthermore, the A91 also presented a significantly up-regulated expression of the ion transporter genes (OsHKT1;3, OsHAK7, and OsSOS1) in the shoot when exposed to salt stress. These findings imply that the OsbHLH024 might play the role of a negative regulator of salt stress, which will help to understand better the molecular basis of rice production improvement under salt stress.

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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.

High temperature (HT) can affect the accumulation of seed storage materials and cause adverse effects on the yield and quality in rice. DNA methylation plays an important role in plant growth and development. However, the temperature and DNA methylation interaction on rice seed development has not been studied yet. Here, we identified a new demethylase gene OsDML4 and discovered its function on cytosine demethylation to affect the endosperm formation during the grain filling. Knockout of OsDML4 induced floury endosperm only under HT, which resulted from dramatically reduced the transcription and accumulation of glutelins and 16-kDa prolamin. The expression of two important transcription factors RISBZ1 and RPBF was significantly declined in the osdml4 mutants. The absence of OsDML4 also caused adverse effects on the formation of protein bodies (PBs), the number of PB-II was greatly decreased and incomplete PB-II with empty space and abnormally shaped PB-II were observed in the osdml4 mutants. 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 (WT). Moreover, the methylation status of RISBZ1 promoter was hypermethylated but RPBF promoter was nearly unchanged. No significant difference was detected between WT and the osdml4 mutants under room temperature. In conclusion, our study demonstrates a novel OsDML4-mediated epigenetic regulatory mechanism involving in the formation of floury endosperm, which will provide a new perspective in regulating endosperm development and the accumulation of SSPs in rice.