Catabolism of jasmonoyl-isoleucine modulates maize development and defense responses

Proper spatial and temporal accumulation of the phytohormone jasmonoyl-isoleucine (JA-Ile) requires precise control of both its biosynthesis and catabolism. Two pathways for JA-Ile catabolism are the conversion of JA-Ile to 12-hydroxy-JA-Ile (12OH-JA-Ile) by JA-Ile hydroxylases, and the reversible deconjugation of isoleucine from JA-Ile by amidohydrolases, followed by conversion of jasmonic acid to 11-hydroxy-jasmonic acid by jasmonate-induced oxygenases. JA-Ile hydroxylase activity is performed by enzymes of the cytochrome P450 94B (CYP94B) family. In this study, we generated single and double loss-of-function mutants of the two CYP94Bs of Zea mays (maize), the JA-Ile hydroxylase ZmCYP94B1 and its paralog ZmCYP94B12 and used these mutants in combination with in vitro and in vivo assays, to explore roles of these genes in JA-Ile catabolism, development, and defense in maize. In vitro assays showed both ZmCYP94B1 and ZmCYP94B12 have JA-Ile hydroxylase activity, and ZmCYP94B1 may also produce 12-carboxy-JA-Ile. Loss of function of both genes in maize leads accumulation of JA-Ile in unstressed leaves, and to enhanced resistance to the insect pest Spodoptera frugiperda and fungal pathogens Cochliobolus heterostrophus and Fusarium verticillioides. This study shows that the JA-Ile hydroxylase pathway plays an important role in JA-Ile catabolism and plant defense in maize. The zmcyp94b mutants also reveal that the genes have roles in regulating plant height and tassel architecture indicating that the ZmCYP94Bs contribute to balancing JA-Ile mediated growth-defense trade-offs.