Identification and Characterization of Jasmonic Acid Methyltransferase Involved in the Formation of Floral Methyl Jasmonate in Hedychium coronarium

Abstract

Hedychium coronarium is a popular ornamental flower in tropical and subtropical areas due to its elegant appearance and inviting fragrance. Methyl jasmonate (MeJA) is one of the volatile compounds in the blooming flowers of H. coronarium. However, the molecular mechanism underlying floral MeJA formation is still unclear in H. coronarium. In this study, a total of 12 SABATH family genes were identified in the genome of H. coronarium, and their encoded proteins range from 366 to 387 amino acids. Phylogenetic analysis revealed seven clades in the SABATH family and a JMT ortholog clade, including two HcSABATH members. Combined with expression profiling of HcSABATH members, HcJMT1 was identified as the top candidate gene for floral MeJA biosynthesis. In vitro enzyme assays showed that HcJMT1 can catalyze the production of MeJA from jasmonic acid. Gene expression analysis indicated that HcJMT1 exhibited the highest expression in the labella and lateral petals, the major sites of MeJA emission. During flower development, the two MeJA isomers, major isomers in the products of the HcJMT1 protein, were released after anthesis, in which stage HcJMT1 displayed high expression. Our results indicated that HcJMT1 is involved in the formation of floral MeJA in H. coronarium.