The tomato MYB21 acts in ovules to mediate jasmonate-regulated fertility (Microarray)

The function of the plant hormone jasmonic acid (JA) in development of tomato flowers was analyzed with a mutant defective in JA perception (jasmonate-insensitive1-1, jai1-1). In contrast to Arabidopsis JA-insensitive plants that are male sterile, the tomato mutant jai1-1 exhibits major defects in female development resulting in female sterility. To identify putative JA-dependent regulatory components, transcriptomics was performed using isolated ovules of three different stages of flower development, from both wild type and jai1-1. Among the strongly down-regulated genes in jai1-1, one encoding a MYB transcription factor (SlMYB21) was found. Its orthologue in Arabidopsis has a crucial role in JA-regulated stamen development. SlMYB21 showed transcription factor activity in yeast, interaction with SlJAZ9 in yeast and in planta, and complemented the Arabidopsis mutant myb21-5. To analyze SlMYB21 function in tomato ovule development, CRISPR/Cas9 mutants were created and a TILLING mutant was identified, all showing female sterility and therefore corroborating a function of MYB21 in tomato ovule development. Transcriptomics from wild type, jai1-1 and myb21-2 carpels revealed processes that might be controlled by SlMYB21. The data suggest a positive regulation of JA biosynthesis by SlMYB21, but a negative regulation of the action of auxin and GA. The results demonstrate that SlMYB21 mediates at least partially the action of JA and might control the flower to fruit transition.