Archana Kumari, Aurore Chételat, Chi Tam Nguyen, and Edward E. Farmer

 PNAS October 1, 2019 116 (40) 20226-20231

 Significance

Phosphorylation (P)-type ATPases act to maintain and modulate charge distribution across membranes and these proteins have been coopted for electrical signaling in animals. When wounded, membranes in the leaves of Arabidopsis thaliana depolarize rapidly. This is followed by a slower repolarization phase. We found that the proton pump AHA1 acted to control membrane potential when these plants were wounded. Specifically, the repolarization phase in aha1 mutants is prolonged relative to that in wild-type plants. In parallel, the jasmonate defense pathway is activated strongly and the mutant plants are better defended against herbivores than the wild type. We reveal that plants, like animals, use P-type ATPases in electrical signaling and show that AHA1 couples membrane potential to anti-herbivore defense.

Abstract

Electrogenic proton pumps have been implicated in the generation of slow wave potentials (SWPs), damage-induced membrane depolarizations that activate the jasmonate (JA) defense pathway in leaves distal to wounds. However, no defined H⁺-ATPases have been shown to modulate these electrical signals. Pilot experiments revealed that the proton pump activator fusicoccin attenuated SWP duration in Arabidopsis. Using mutant analyses, we identified Arabidopsis H⁺-ATPase 1 (AHA1) as a SWP regulator. The duration of the repolarization phase was strongly extended in reduced function aha1 mutants. Moreover, the duration of SWP repolarization was shortened in the presence of a gain-of-function AHA1 allele. We employed aphid electrodes to probe the effects of the aha1 mutation on wound-stimulated electrical activity in the phloem. Relative to the wild type, the aha1-7 mutant increased the duration and reduced the amplitudes of electrical signals in sieve tube cells. In addition to affecting electrical signaling, expression of the JA pathway marker gene JAZ10 in leaves distal to wounds was enhanced in aha1-7. Consistent with this, levels of wound-response jasmonoyl-isoleucine were enhanced in the mutant, as was defense against a lepidopteran herbivore. The work identifies a discrete member of the P-type ATPase superfamily with a role in leaf-to-leaf electrical signaling and plant defense.

See https://www.pnas.org/content/116/40/20226

Figure 1: Phenotype and wound-activated surface potential measurements in aha1-7, complemented aha1-7, and ost2-2D. (A) Five weeks-old wild-type (WT) rosette, +/aha1-7, and aha1-7/ aha1-7 rosettes. (B) Surface potential changes on leaf 8. Broken columns indicate measurements after wounding where repolarization taking more than 300 s was not quantified. (C) Surface potentials on distal leaf 13. (D) Five weeks-old WT, aha1-7, and aha1-7 complemented with AHA1p::AHA1-Venus. (E) Wound-activated surface potential changes on leaf 8, and (F) on distal leaf 13 (n = 10–12). (G and H) Wound-activated surface potential changes in distal leaf 13 of ost2-2D. (G) Amplitude and (H) duration, (n = 15). Data shown are means ± SD. Asterisks indicate a significant difference with WT. Student t test: *P < 0.05, **P < 0.01.