Mutation of ACX1 , a Jasmonic Acid Biosynthetic Enzyme, Leads to Petal Degeneration in Chinese Cabbage ( Brassica campestris ssp. pekinensis )

Petal color, size, and morphology play important roles in protecting other floral organs, attracting pollinators, and facilitating sexual reproduction in plants. In a previous study, we obtained a petal degeneration mutant ( ) from the 'FT' doubled haploid line of Chinese cabbage and found that the candidate gene for , , encodes the enzyme acyl-CoA oxidase1. In this study, we sought to examine the gene networks regulating petal development in plants. We show that the mRNA and protein expression of , which is involved in the jasmonic acid (JA) biosynthetic pathway, were significantly lower in the petals of plants than in those of 'FT' plants. Similarly, the JA and methyl jasmonate (MeJA) contents of petals were significantly lower in plants than in 'FT' plants and we found that exogenous application of these hormones to the inflorescences of plants restored the 'FT' phenotype. Comparative analyses of the transcriptomes of 'FT', and + JA (pJA) plants revealed 10,160 differentially expressed genes (DEGs) with consistent expression tendencies in 'FT' vs. and pJA vs. comparisons. Among these DEGs, we identified 69 DEGs related to floral organ development, 11 of which are involved in petal development regulated by JA. On the basis of qRT-PCR verification, we propose regulatory pathways whereby JA may mediate petal development in the mutant. We demonstrate that mutation of in plants leads to reduced JA levels and that this in turn promotes changes in the expression of genes that are expressed in response to JA, ultimately resulting in petal degeneration. These findings thus indicate that JA is associated with petal development in Chinese cabbage. These results enhance our knowledge on the molecular mechanisms underlying petal development and lay the foundations for further elucidation of the mechanisms associated with floral organ development in Chinese cabbage.