Dynamic monitoring of TGW6 by selective autophagy during grain development in rice

Crop yield must increase to achieve food security in the face of a growing population and environmental deterioration. Grain size is a prime breeding target for improving grain yield and quality in crop. Here, we report that autophagy emerges as an important regulatory pathway contributing to grain size and quality in rice. Mutations of rice Autophagy-related 9b (OsATG9b) or OsATG13a causes smaller grains and increase of chalkiness, whereas overexpression of either promotes grain size and quality. We also demonstrate that THOUSAND-GRAIN WEIGHT 6 (TGW6), a superior allele that regulates grain size and quality in the rice variety Kasalath, interacts with OsATG8 via the canonical Atg8-interacting motif (AIM), and then is recruited to the autophagosome for selective degradation. In consistent, alteration of either OsATG9b or OsATG13a expression results in reciprocal modulation of TGW6 abundance during grain growth. Genetic analyses confirmed that knockout of TGW6 in either osatg9b or osatg13a mutants can partially rescue their grain size defects, indicating that TGW6 is one of the substrates for autophagy to regulate grain development. We therefore propose a potential framework for autophagy in contributing to grain size and quality in crops.