Gibberellin signaling regulates lignin biosynthesis to modulate rice seed shattering.

The elimination of seed shattering was a key step in rice (Oryza sativa) domestication. In this paper, we show that increasing the gibberellic acid (GA) content or response in the abscission region enhanced seed shattering in rice. We demonstrate that SLENDER RICE1 (SLR1), the key repressor of GA signaling, could physically interact with the rice seed shattering-related transcription factors QTL of seed shattering on chromosome 1 (qSH1), Oryza sativa HOMEOBOX 15 (OSH15), and SUPERNUMERARY BRACT GENE (SNB). Importantly, these physical interactions interfered with the direct binding of these three regulators to the lignin biosynthesis gene4-COUMARATE:COENZYME A LIGASE 3 (4CL3), thereby de-repressing its expression. De-repression of 4CL3 led to increased lignin deposition in the abscission region, causing reduced rice seed shattering. Importantly, we also show that modulating GA content could alter the degree of seed shattering to increase harvest efficiency. Our results reveal that the "Green Revolution" phytohormone GA is important for regulating rice seed shattering, and we provide an applicable breeding strategy for high-efficiency rice harvesting.