Mutation in BnaCMA disrupts style morphology, transmitting tract formation, and silique length in Brassica napus

The female reproductive organ is essential for crop yield, but the mechanism underlying its development remains unclear in Brassica napus. Here, we identified four BnaCMA (Carpel Morphogenesis Abnormality) homologs, which play key roles in regulating gynoecium and silique development in B. napus. The BnaCMA triple mutants exhibited severe and penetrant abnormalities in the female reproductive organ, characterized by bifurcated styles, shortened siliques, and a total absence of seeds. These mutants exhibited a diminished transmitting tract and obstructed pollen tube elongation. The BnaCMA single mutants showed only less severe impairments in silique elongation. Genetic and molecular analyses demonstrated that BnaCMA directly interacts with BnaC09T0533300WE to control gynoecium and silique development. Furthermore, transcriptome analysis revealed that BnaCMA and BnaC09T0533300WE modulate the expression of multiple auxin response genes. Exogenous auxin treatment rescued the pistil length in mutants, indicating that BnaCMA and BnaC09T0533300WE regulate the sensitivity to auxin during gynoecium development. Altogether, our results elucidate a novel regulatory pathway in which BnaCMA interacts with BnaC09T0533300WE, orchestrating pistil and silique development through the auxin signaling pathway. These findings provide prospective genetic resources for molecular breeding aimed at enhancing yield and fertility in B. napus.