ITPK1 regulates jasmonate-controlled root development in Arabidopsis thaliana

Jasmonic acid (JA) is a plant hormone that regulates a plethora of physiological processes including immunity and development and is perceived by the F-Box protein, Coronatine-insensitive protein 1(COI1). The discovery of inositol phosphates (InsPs) in the COI1 receptor complex highlights their role in JA perception. InsPs are phosphate-rich signaling molecules that control many aspects of plant physiology. Inositol pyrophosphates (PP-InsPs) are diphosphate containing InsP species of which InsP7 and InsP8 are the best characterized ones. Different InsP and PP-InsP species are linked with JA-related plant immunity. However, role of PP-InsP species in regulating JA-dependent developmental processes are poorly understood. Recent identification of ITPK1 kinase responsible for the production of 5-InsP7 from InsP6 in planta provides a platform to interrogate possible involvement of ITPK-derived InsP species in JA-related plant development. Herein this study, we report that ITPK1-defective plants exhibit increased root growth inhibition to bioactive JA treatment. The itpk1 plants also show increased lateral root density when treated with JA. Notably, JA treatment does not induce ITPK1 protein level. Gene expression analyses revealed that JA-biosynthetic genes are not differentially expressed in the ITPK1-deficient plants. We further demonstrate that genes encoding different JAZ repressor proteins are severely downregulated in the ITPK1-defective plants. Taken together, our study highlights the role of ITPK1 in regulating JA-dependent root architecture development through controlling expression of different JAZ repressor proteins.