Abscinazole E3M, a practical inhibitor of abscisic acid 8' hydroxylase for improving drought tolerance
Abscisic acid (ABA) is an essential phytohormone that regulates plant water use and drought tolerance. However, agricultural applications of ABA have been limited because of its rapid inactivation in plants, which involves hydroxylation of ABA by ABA 8' hydroxylase (CYP707A) We previously developed a selective inhibitor of CYP707A, Abz E2B, by structurally modifying S uniconazole, which functions as an inhibitor of CYP707A and as a gibberellin biosynthetic enzyme. However, its synthetic yield is too low for practical applications. Therefore, we designed novel CYP707A inhibitors, Abz T compounds, that have simpler structures in which the 1,2,3 triazolyl ring of Abz E2B has been replaced with a triple bond. They were successfully synthesised in shorter steps, resulting in greater yields than that of Abz E2B. In the enzymatic assays, one of the Abz T compounds, Abz E3M, acted as a strong and selective inhibitor of CYP707A, similar to Abz E2B. Analysis of the biological effects in Arabidopsis revealed that Abz E3M enhanced ABA's effects more than Abz E2B in seed germination and in the expression of ABA responsive genes. Treatment with Abz E3M induced stomatal closure and improved drought tolerance in Arabidopsis. Furthermore, Abz E3M also increased the ABA response in rice and maize. Thus, Abz E3M is a more practical and effective inhibitor of CYP707A than Abz E2B.
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