Chemical Genetics Reveals Negative Regulation of Abscisic Acid Signaling by a Plant Immune Response Pathway

Abstract

Summary Coordinated regulation of protection mechanisms against environmental abiotic stress and pathogen attack is essential for plant adaptation and survival. Initial abiotic stress can interfere with disease resistance signaling [1–6]. Conversely, initial plant immune signaling may interrupt subsequent ABA signal transduction [7, 8]. However, the processes involved in cross talk between these signaling networks have not been determined. By screening a 9,600 compound chemical library, we identified a small molecule DFPM that rapidly down-regulates ABA-dependent gene expression and also inhibits ABA-induced stomatal closure. Transcriptome analyses show that DFPM also stimulates expression of plant defense-related genes. Major early regulators of pathogen resistance responses, including EDS1, PAD4, RAR1, and SGT1b, are required for DFPM- and notably also for Pseudomonas-interference with ABA signal transduction, whereas salicylic acid, EDS16 and NPR1 are not necessary. While DFPM does not interfere with early ABA perception by PYR/RCAR receptors or ABA-activation of SnRK2 kinases, it disrupts cytosolic Ca2+ signaling and downstream anion channel activation in a pad4-dependent manner. Our findings provide evidence that activation of EDS1/PAD4-dependent plant immune responses rapidly disrupts ABA signal transduction and this occurs at the level of Ca2+ signaling, illuminating how the initial biotic stress pathway interferes with ABA signaling.

Environmental Nitrate Stimulates Abscisic Acid Accumulation in Arabidopsis Root Tips by Releasing It from Inactive Stores

“…We measured the expression of a set of three ABA-responsive genes, ABA-INSENSITIVE5 (ABI5) (Finkelstein and Lynch, 2000), RESPONSIVE TO ABA18 (RAB18) (Kim et al, 2011), and RESPONSIVE TO DESSICATION29A (RD29A) (Yamaguchi-Shinozaki and Shinozaki, 1993); three NO 3 2 -inducible genes, NITRATE REDUCTASE1 (NIA1) (Parinov et al, 1999), NIA2 (Wilkinson and Crawford, 1991), and NITRITE REDUCTASE1 (NIR1) (Hwang et al, 1997); the ABA biosynthesis gene ABA DEFICIENT2 (ABA2) (Léon-Kloosterziel et al, 1996); and ABA deconjugation enzyme BG2 (Xu et al, 2012; Figure 4P) in (A) ABA immunofluorescence intensity plotted as a percentage of intensity in control roots or roots treated for 2 d with either KCl, ABA, or KNO 3 . Fluorescence intensity was measured as the sum of total fluorescence of the transverse or vertical line scans of treated and untreated roots (n = 10 roots for each column).…”

Plant Stress Surveillance Monitored by ABA and Disease Signaling Interactions

“…SA signaling and the EDS16 and NONEXPRESSER OF PR GENES1 (NPR1) loci were not necessary for this interference of ABA signaling, demonstrating a difference to the converse ABA interference of biotic stress signaling. DFPM interference of ABA signaling occurs at the events downstream of intracellular Ca 2+ and Ca 2+ -activation of anion channels, where-as upstream ABA signaling events involving PYR/PYL/RCAR receptors and SnRK2 kinase activation were not affected by DFPM treatment (Kim et al, 2011) (Fig. 2).…”

“…Another evidence revealing NB-LRR receptors as an important regulator of ABA signal transduction was presented based on the finding of novel small compound DFPM and the following chemical genetics approach (Kim et al, 2011) (Fig. 1).…”

“…Gene expression and genetic analyses of DFPM indicated that ABA signaling interference by DFPM was caused by activation of NB-LRR and subsequent signaling pathways. As induction of disease response pathways by DFPM efficiently interfered with guard cell ABA signal transduction, plant infection by Pseudomonas syringae affected negatively ABA-induction of gene expression as well as ABAinduced stomatal closures (Kim et al, 2011). Notably, analyses of pathogen signaling mutants showed that major early regulators of effector-triggered immunity pathways, including EDS1, PHYTOALEXIN DEFICIENT4 (PAD4), REQUIRED FOR Mla12 RESISTANCE (RAR1), and SUPPRESSOR OF G2 ALLELE OF SKP1B (SGT1B), are required for the DFPM-as well as for biological Pseudomonas-inhibition of ABA signal transduction.…”

“…At low levels of calcium, the middle autoinhibitory domain, which is intervening between kinase and calmodulin-like domains, suppresses the kinase activity of CDPKs. With previous reports on the roles of CDPKs in abiotic signal transduction as well as during biotic disease stress responses (Ludwig et al, 2004), CDPK is proposed as a candidate regulator to function through Ca 2+ signals at the point of ABA and disease signaling interactions (Kim et al, 2011). The Arabidopsis genome has 34 CDPK genes.…”