Environmental Regulation Of Stomate-based Defense Against Bacterial Infection in Arabidopsis

Stomata are natural openings in the plant epidermis responsible for gas (O2 and CO2) exchange between plant interior and environment. They are formed by a pair of guard cells, which are able to close the stomatal pore in response to a number of external factors including light intensity, carbon dioxide concentration, and relative humidity. The stomatal pore is also the main route for pathogen entry into leaves, a crucial step for disease development. Recent studies have unveiled that closure of the pore is effective in preventing bacterial disease in Arabidopsis plants and the successful plant pathogen Pseudomonas syringae pv. tomato (Pst)DC3000 is able to re-open stomata by producing the phytotoxin coronatine. A major unanswered question is: "how do stomata respond to combined effect of biotic and abiotic stresses?" I found that coronatine can re-open dark-closed stomata as early as three hours post-incubation with purified coronatine or the coronatine producing Pst DC3000. Same trend did not hold for the coronatine deficient mutants, Pst DC3118 and Pst DB29. Moreover, diseaseexhibited by plants infected with Pst DC3000 was significantly severe even in dark. I also have evidence that high relative humidity (RH; 95 ± 5%) reduces bacterium-triggered stomatal closure. The same effect was not observed under low RH (60 ± 5%). Taken together, these results suggest that guard cells prioritize their response when exposed to multiple stimuli. Understanding this process should help elucidating the effectiveness of stomatal-based defense in nature where plant experiences constant influx of external stimuli and also implementing additional measures to control disease outbreaks in the field.