The chalkiness, starch fine structure, and physiochemical properties of rice starch were analyzed and their correlations were investigated under different nighttime temperatures during the early grain-filling stage. Compared to MT, medium temperature (MT) and low (LNT) and high (HNT) nighttime temperatures resulted in an increased chalky grain rate (CGR) and chalkiness degree (CD). LNT mainly affected the chalkiness by increasing peak1 (short branch chains of amylopectin), the branching degree, and the proportion of small starch granules but decreasing peak2 (long branch chains of amylopectin) and peak3 (amylose branches). This altered the pasting properties, such as by increasing the peak viscosity and final viscosity. However, HNT mainly affected the chalkiness by increasing peak2 and the crystallinity degree but decreasing peak1 and peak3. Regarding the thermal properties, HNT also elevated peak and conclusion temperatures. The CGR and CD were significantly and positively correlated with the proportions of small and medium starch granules, peak1, branching degree, gelatinization enthalpy, setback viscosity, and pasting time but markedly and negatively correlated with the proportion of large starch granules, amylose content, peak3, peak viscosity, and breakdown viscosity. These findings suggest that LNT and HNT disrupted the starch structure, resulting in increased chalkiness. However, their mechanisms of action differ.

The AP2/ERF transcription factor ABSCISIC ACID INSENSITIVE 4 (ABI4) plays diverse roles in plant development and responses to abiotic stress. However, its potential involvement in regulating anthocyanin biosynthesis is not fully understood. In this study, three different loss-of-function abi4 alleles (abi4-1, abi4-2, and abi4-101) were employed to investigate the role of ABI4 in the regulation of anthocyanin accumulation in Arabidopsis seedlings. These abi4 mutants exhibited significantly increased anthocyanin accumulation, which was associated with elevated expression of genes involved in anthocyanin biosynthesis. HY5 (LONG HYPOCOTYL 5), a central component of photomorphogenesis, acts as a key light-regulated molecular switch. Further analysis revealed that ABI4 requires HY5 to function as a negative regulator of anthocyanin biosynthesis. Additionally, loss of ABI4 resulted in heightened light sensitivity, leading to increased light-induced chlorophyll accumulation and chloroplast development, along with upregulation of photosynthesis-related genes. Interestingly, the light-hypersensitive phenotype of abi4 mutants was partially rescued by the loss of HY5 function. Taken together, these findings demonstrate that ABI4 negatively regulates anthocyanin accumulation in Arabidopsis seedlings through a HY5-dependent light signaling pathway.

Although the role of OsHY5L2 in promoting photomorphogenic development is well characterized, its function in regulating rice quality is poorly understood. In this study, we found that OsHY5L2 plays an important role in regulating starch metabolism and modulating its fine structure and physicochemical properties. Overexpression of OsHY5L2 significantly reduced the chalky grain rate and degree of chalkiness but dramatically increased the head rice rate. OsHY5L2 was found to negatively regulate the accumulation of starch in rice endosperm by inhibiting starch biosynthesis and promoting starch hydrolysis. Transcriptomic analysis revealed that OsHY5L2 mainly regulated the expression of genes encoding enzymes involved in starch and sucrose metabolism. Moreover, OsHY5L2 overexpression induced the formation of numerous pinhole structures on the surfaces of starch granules. Analysis of the amylopectin chain length distribution showed that overexpression of OsHY5L2 decreased the proportion of ultra-short chains (DP 6–7) and intermediate chains (DP 13–24) of amylopectin while increasing the proportion of short chains (DP 8–12) and long chains (DP 25–36). Further studies demonstrate that OsHY5L2 overexpression altered the pasting properties of rice starch by affecting its multi-level structure and function. The results of this study improve our understanding of the functions of OsHY5L2 in regulating rice quality.