A new role for green leaf volatile esters in tomato stomatal defense against Pseudomonas syringe pv. tomato

[EN] The volatile esters of (Z)-3-hexenol with acetic, propionic, isobutyric, or butyric acids are synthesized by alcohol acyltransferases (AAT) in plants. These compounds are differentially emitted when tomato plants are efficiently resisting an infection with Pseudomonas syringae pv. tomato. We have studied the defensive role of these green leaf volatile (GLV) esters in the tomato response to bacterial infection, by analyzing the induction of resistance mediated by these GLVs and the phenotype upon bacterial infection of tomato plants impaired in their biosynthesis. We observed that treatments of plants with (Z)-3-hexenyl propionate (HP) and, to a greater extent with (Z)-3-hexenyl butyrate (HB), resulted in stomatal closure, PR gene induction and enhanced resistance to the bacteria. HB-mediated stomatal closure was also effective in several plant species belonging to Nicotiana, Arabidopsis, Medicago, Zea and Citrus genus, and both stomatal closure and resistance were induced in HB-treated NahG tomato plants, which are deficient in salicylic acid (SA) accumulation. Transgenic antisense AAT1 tomato plants, which displayed a reduction of ester emissions upon bacterial infection in leaves, exhibited a lower ratio of stomatal closure and were hyper-susceptible to bacterial infection. Our results confirm the role of GLV esters in plant immunity, uncovering a SA-independent effect of HB in stomatal defense. Moreover, we identified HB as a natural stomatal closure compound with potential agricultural applications.This work was funded by Grant AICO/2017/048 from the Generalitat Valenciana and by Grant INNVAL10/18/005 from the Agencia Valenciana de la Innovacio (Spain). We would like to thank the Metabolomics Service of the IBMCP (Valencia, Spain), especially to Teresa Caballero for her excellent technical support in the VOCs quantification. We also thank Eduardo Moya for technical assistance.López-Gresa, MP.; Payá, C.; Ozáez-Martínez, M.; Rodrigo Bravo, I.; Conejero Tomás, V.; Klee, H.; Belles Albert, JM.... (2018). A new role for green leaf volatile esters in tomato stomatal defense against Pseudomonas syringe pv. tomato. Frontiers in Plant Science. 9:1-12. https://doi.org/10.3389/fpls.2018.01855112