Regulation of Grain Chalkiness and Starch Metabolism by FLO2 Interaction Factor 3, a bHLH Transcription Factor in .

Chalkiness is a key determinant that directly affects the appearance and cooking quality of rice grains. Previously, () was reported to be involved in the formation of rice chalkiness; however, its regulation mechanism is still unclear. Here, FLO2 interaction factor 3 (FIF3), a bHLH transcription factor, was identified and analyzed in . A significant increase in chalkiness was observed in -overexpressed grains, coupled with a round, hollow filling of starch granules and reduced grain weight. FIF3 is evolutionarily conserved in monocotyledons, but variable in dicotyledons. Subcellular localization revealed the predominant localization of FIF3 in the nucleus. The DAP-seq (DNA affinity purification sequencing) results showed that FIF3 could affect the transcriptional accumulation of , , , , , (), and through the binding of the CACGTG motif on their promoters. Moreover, and with abundant FIF3 binding signals showed significant expression reduction in overexpression lines, further confirming FIF3's role in starch metabolism regulation and energy material allocation. Taken together, these findings show that the overexpression of inhibits the expression of and , thereby increasing grain chalkiness and affecting grain weight.