The TIFY family protein CmJAZ1‐like negatively regulates petal size via interaction with the bHLH transcription factor CmBPE2 in Chrysanthemum morifolium

SUMMARY Petals are the second floral whorl of angiosperms, exhibiting astonishing diversity in their size between and within species. This variation is essential for protecting their inner reproductive organs and attracting pollinators for fertilization. However, currently, the genetic and developmental control of petal size remains unexplored. Chrysanthemum ( Chrysanthemum morifolium ) belongs to the Asteraceae family, the largest group of angiosperms , and the extraordinary diversity of petal size in chrysanthemums makes it an ideal model for exploring the regulation mechanism of petal size. Here, we reveal that overexpression of a JAZ repressor CmJAZ1‐like exhibits decreased petal size compared to that of the wild‐type as a result of repressed cell expansion. Through further in‐depth exploration, we confirm an interaction pair between CmJAZ1‐like and the bHLH transcription factor CmBPE2. The inhibition of CmBPE2 expression negatively regulates petal size by downregulating the expression of genes involved in cell expansion. Furthermore, CmJAZ1‐like significantly reduced the activation ability of CmBPE2 on its target gene CmEXPA7 by directly interacting with it, thus participating in the regulation of petal size development in chrysanthemum. Our results will provide insights into the molecular mechanisms of petal size regulation in flowering plants.