Palea and grain shrunken encoding OsMADS15 determines palea identity to affect rice grain yield and quality

The hull, composed of the lemma and palea, defines rice grain morphology and influences endosperm filling and quality. However, how palea development affects grain filling and quality remains poorly understood. Here, we identify a rice mutant, palea and grain shrunken 1 (pgs1), which exhibits a markedly reduced palea and elongated sterile lemmas. MutMap-based cloning reveals that PGS1 encodes the MADS-box transcription factor OsMADS15. The pgs1 mutant shows smaller but denser grains with substantially reduced chalkiness, and the expression of several palea identity genes, including G1, OsMADS1, and SL1, is significantly decreased. PGS1 is expressed in multiple floral organs, localizes to the nucleus, and lacks intrinsic transcriptional activation activity. Protein interaction assays show that PGS1 physically interacts with the histone demethylase JMJ706, and JMJ706 knockout lines exhibit floral and grain phenotypes similar to those of pgs1. Together, these results support a functional association between PGS1 and JMJ706 in the regulation of palea development and further suggest that defective palea development affects grain filling and grain quality in rice.