MODULATION OF STOMATAL APERTURE BY BENEFICIAL ENDOPHYTIC BACTERIA

COPPOLA-GUERREIRO F; STELLA G; ROMERO FM; TOUM L; SANNAZZARO A; ESTRELLA MJ; GUDESBLAT GE; PIECKENSTAIN FL

Workshop; III Latin American PGPR Workshop; 2016

Plant leaves normally host a large number of species of endophytic bacteria. Some of them can protect host plants from pathogens, and foliar inoculation of beneficial bacteria is a common practice in agriculture. It has been proposed that beneficial leaf endophytic bacteria colonize leaves through stomata, but stomata can close in response to bacterial MAMPs thus limiting bacterial penetration through them, a phenomenon known as stomatal immunity. Phytopathogenic bacteria such as Pseudomonas syringae and Xanthomonas campestris have evolved mechanisms to inhibit stomatal immunity through the synthesis of diffusible toxins, or through degradation of their own MAMPs. However, the possible existence of such mechanisms in non-pathogenic, leaf-associated bacteria has not been studied. On this basis, our goals are: 1) To determine if bacteria isolated from leaves which are capable of conferring protection against pathogens are able to inhibit stomatal immunity, and if such inhibition aids them to colonize leaves through stomatal pores. 2) To determine if the protective effect of certain bacteria against foliar pathogens depends on the ability of the former to access and colonize leaves through stomata.To attain these goals, we obtained a collection of bacteria associated to leaves of horticultural crops. We identified both innocuous and beneficial bacteria that either showed reduced promotion of stomatal closure, or induced stomatal re-aperture after initial closing in tomato, Arabidopsis and broad bean. We observed that cell-free culture filtrates from some of these isolates inhibited stomatal closure triggered by abscisic acid or the flagellin-derived peptide flg22. These results suggest that these bacteria are able either to evade or inhibit stomatal immunity. Some of these isolates were also capable of protecting leaves against gray mold caused by the fungus Botrytis cinerea. Current work is in progress to determine if the ability to manipulate stomatal aperture increases bacterial potential for endophytic colonization and protection against this and other pathogens.