Purple Acid Phosphatase5 is required for maintaining basal resistance against Pseudomonas syringaein Arabidopsis

Sridhar Ravichandran,Bernhard Benkel,Balakrishnan Prithiviraj,Sophia L Stone

doi:10.1186/1471-2229-13-107

Abstract

BackgroundPlants have evolved an array of constitutive and inducible defense strategies to restrict pathogen ingress. However, some pathogens still manage to invade plants and impair growth and productivity. Previous studies have revealed several key regulators of defense responses, and efforts have been made to use this information to develop disease resistant crop plants. These efforts are often hampered by the complexity of defense signaling pathways. To further elucidate the complexity of defense responses, we screened a population of T-DNA mutants in Colombia-0 background that displayed altered defense responses to virulent Pseudomonas syringae pv. tomato DC3000 (Pst DC3000).ResultsIn this study, we demonstrated that the Arabidopsis Purple Acid Phosphatse5 (PAP5) gene, induced under prolonged phosphate (Pi) starvation, is required for maintaining basal resistance to certain pathogens. The expression of PAP5 was distinctly induced only under prolonged Pi starvation and during the early stage of Pst DC3000 infection (6 h.p.i). T-DNA tagged mutant pap5 displayed enhanced susceptibility to the virulent bacterial pathogen Pst DC3000. The pap5 mutation greatly reduced the expression of pathogen inducible gene PR1 compared to wild-type plants. Similarly, other defense related genes including ICS1 and PDF1.2 were impaired in pap5 plants. Moreover, application of BTH (an analog of SA) restored PR1 expression in pap5 plants.ConclusionTaken together, our results demonstrate the requirement of PAP5 for maintaining basal resistance against Pst DC3000. Furthermore, our results provide evidence that PAP5 acts upstream of SA accumulation to regulate the expression of other defense responsive genes. We also provide the first experimental evidence indicating the role PAP5 in plant defense responses.

Highlights

Plants have evolved an array of constitutive and inducible defense strategies to restrict pathogen ingress
Identification of mutants exhibiting altered defense responses One thousand two hundred unique Arabidopsis thaliana T-DNA insertion lines were spray inoculated with the virulent isolate of Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) and monitored for altered responses to the pathogen
The enhanced susceptibility phenotype of pap5-1 plants was confirmed by assessing bacterial growth in leaf tissues post inoculation

Summary

Introduction

Plants have evolved an array of constitutive and inducible defense strategies to restrict pathogen ingress. Previous studies have revealed several key regulators of defense responses, and efforts have been made to use this information to develop disease resistant crop plants. These efforts are often hampered by the complexity of defense signaling pathways. In recent years other phytohormones including abscisic acid (ABA), auxins, gibberellins (GA), cytokines (CK) and brassinosteriods (BR) have been shown to mediate specific plant defense responses (reviewed in [2,10]). As plants are exposed to an array of pathogens with diverse infection strategies, activation of appropriate, pathogenspecific defense responses is vital for plant growth and productivity [11]

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