The bHLH transcription factor PIL1 orchestrates starch synthesis in key cereal crops

Key cereal crops, including wheat, rice and maize, supply nearly 50% of the world's caloric intake, with starch constituting over 70% of the grain weight. However, the regulatory mechanisms underlying starch synthesis are poorly understood. In this study, we identify a transcription factor TaPIL1-5D, which binds to the promoters of ADP-glucose pyrophosphorylase small subunit 1 (TaAGPS1a-7A), granule-bound starch synthase I (TaGBSSI-4A), and branching enzyme II b (TaBEIIb-2D). Similarly, its homologous OsPIL11 and ZmPIL1 also activate the expression of the AGPS1, BEIIb, and GBSSI, and positively regulates grain starch synthesis. TaPIL1-5D and ZmPIL1 improve grain yields in two successive years. Nine alleles of TaPIL1-5B form three distinct haplotypes (Hap1-3), while TaPIL1-5B-Hap1 is repressed due to its binding by the transcriptional repressor TaBZR1.1. Additionally, TaPIL1-5B interacts with TaPIL1-5D in the nucleus, enhancing its transcriptional activation. Collectively, our study enriches the starch regulatory network and provides a promising tool for improving starch content.