Arabidopsis inositol polyphosphate kinases IPK1 and ITPK1 modulate crosstalk between SA-dependent immunity and phosphate-starvation responses

Abstract

Selective Arabidopsis thaliana inositol phosphate kinase functions modulate response amplitudes in innate immunity by balancing signalling adjustments with phosphate homeostasis networks. Pyrophosphorylation of InsP₆ generates InsP₇ and/or InsP₈ containing high-energy phosphoanhydride bonds that are harnessed during energy requirements of a cell. As bona fide co-factors for several phytohormone networks, InsP₇/InsP₈ modulate key developmental processes. With requirements in transducing jasmonic acid (JA) and phosphate-starvation responses (PSR), InsP₈ exemplifies a versatile metabolite for crosstalks between different cellular pathways during diverse stress exposures. Here we show that Arabidopsis thaliana INOSITOL PENTAKISPHOSPHATE 2-KINASE 1 (IPK1), INOSITOL 1,3,4-TRISPHOSPHATE 5/6-KINASE 1 (ITPK1), and DIPHOSPHOINOSITOL PENTAKISPHOSPHATE KINASE 2 (VIH2) implicated in InsP₈ biosynthesis, suppress salicylic acid (SA)-dependent immunity. In ipk1, itpk1 or vih2 mutants, constitutive activation of defenses lead to enhanced resistance against the Pseudomonas syringae pv tomato DC3000 (PstDC3000) strain. Our data reveal that upregulated SA-signaling sectors potentiate increased expression of several phosphate-starvation inducible (PSI)-genes, previously known in these mutants. In reciprocation, upregulated PSI-genes moderate expression amplitudes of defense-associated markers. We demonstrate that SA is induced in phosphate-deprived plants, however its defense-promoting functions are likely diverted to PSR-supportive roles. Overall, our investigations reveal selective InsPs as crosstalk mediators in defense-phosphate homeostasis and in reprogramming stress-appropriate response intensities.

Keywords: Arabidopsis thaliana; Basal immunity; Inositol polyphosphates; Phosphate-starvation response; PstDC3000; Salicylic acid.