Danger-Associated Peptides Close Stomata by OST1-Independent Activation of Anion Channels in Guard Cells

Abstract

The plant elicitor peptides (Peps), a family of damage/danger-associated molecular patterns (DAMPs), are perceived by two receptors, PEPR1 and PEPR2, and contribute to plant defense against pathogen attack and abiotic stress. Here, we show that the Peps-PEPR signaling pathway functions in stomatal immunity by activating guard cell anion channels in <i>Arabidopsis thaliana</i> The mutant plants lacking both <i>PEPR1</i> and <i>PEPR2</i> (<i>pepr1 pepr2</i>) displayed enhanced bacterial growth after being sprayed with <i>Pseudomonas syringae</i> pv <i>tomato</i> (<i>Pst</i>) DC3000, but not after pathogen infiltration into leaves, implicating PEPR function in stomatal immunity. Indeed, synthetic Arabidopsis Peps (<i>At</i>Peps) effectively induced stomatal closure in wild-type but not <i>pepr1 pepr2</i> mutant leaves, suggesting that the <i>At</i>Peps-PEPR signaling pathway triggers stomatal closure. Consistent with this finding, patch-clamp recording revealed <i>At</i>Pep1-induced activation of anion channels in the guard cells of wild-type but not <i>pepr1 pepr2</i> mutant plants. We further identified two guard cell-expressed anion channels, SLOW ANION CHANNEL1 (SLAC1) and its homolog SLAH3, as functionally overlapping components responsible for <i>At</i>Pep1-induced stomatal closure. The <i>slac1 slah3</i> double mutant, but not <i>slac1</i> or <i>slah3</i> single mutants, failed to respond to <i>At</i>Pep1 in stomatal closure assays. Interestingly, disruption of <i>OPEN STOMATA1</i> (<i>OST1</i>), an essential gene for abscisic acid-triggered stomatal closure, did not affect the <i>At</i>Pep1-induced anion channel activity and stomatal response. Together, these results illustrate a DAMP-triggered signaling pathway that, unlike the flagellin22-FLAGELLIN-SENSITIVE2 pathway, triggers stomata immunity through an OST1-independent mechanism.