AUTHOR=Hung Chiu-Yueh , Aspesi Jr Peter , Hunter Melissa R. , Lomax Aaron W. , Perera Imara Y. 

TITLE=Phosphoinositide-signaling is one component of a robust plant defense response

JOURNAL=Frontiers in Plant Science

VOLUME=5

YEAR=2014

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2014.00267

DOI=10.3389/fpls.2014.00267

ISSN=1664-462X

ABSTRACT=<p>The phosphoinositide pathway and inositol-1,4,5-triphosphate (InsP<sub>3</sub>) have been implicated in plant responses to many abiotic stresses; however, their role in response to biotic stress is not well characterized. In the current study, we show that both basal defense and systemic acquired resistance responses are affected in transgenic plants constitutively expressing the human type I inositol polyphosphate 5-phosphatase (InsP 5-ptase) which have greatly reduced InsP<sub>3</sub> levels. Flagellin induced Ca<sup>2+</sup>-release as well as the expressions of some flg22 responsive genes were attenuated in the InsP 5-ptase plants. Furthermore, the InsP 5-ptase plants were more susceptible to virulent and avirulent strains of <italic>Pseudomonas syringae</italic> pv. <italic>tomato</italic> (<italic>Pst</italic>) <italic>DC3000</italic>. The InsP 5-ptase plants had lower basal salicylic acid (SA) levels and the induction of SAR in systemic leaves was reduced and delayed. Reciprocal exudate experiments showed that although the InsP 5-ptase plants produced equally effective molecules that could trigger <italic>PR-1</italic> gene expression in wild type plants, exudates collected from either wild type or InsP 5-ptase plants triggered less <italic>PR-1</italic> gene expression in InsP 5-ptase plants. Additionally, expression profiles indicated that several defense genes including <italic>PR-1</italic>, <italic>PR-2</italic>, <italic>PR-5</italic>, and <italic>AIG1</italic> were basally down regulated in the InsP 5-ptase plants compared with wild type. Upon pathogen attack, expression of these genes was either not induced or showed delayed induction in systemic leaves. Our study shows that phosphoinositide signaling is one component of the plant defense network and is involved in both basal and systemic responses. The dampening of InsP<sub>3</sub>-mediated signaling affects Ca<sup>2+</sup> release, modulates defense gene expression and compromises plant defense responses.</p>