Research assistant University of Florida GAINESVILLE, Florida
Body of Abstract: There is a tremendous yield loss of crops worldwide due to diseases caused by microbial pathogens. Many pathogens are inhabitants of the phyllosphere, using stomata as their primary route of entry. Stomatal pores formed by pairs of specialized guard cells in the leaf epidermis open and close to regulate CO2 intake and transpirational water loss. Plant pathogens have long been known to exploit stomatal pores as major entry points to the intracellular leaf space. Conversely, plants have evolved immune mechanisms to limit pathogen entry into the plant body. Efficient detection of pathogens and mounting of timely defense responses are essential for plant survival and crop viability.
Lipoxygenases (LOX) are non-heme iron-containing dioxygenases, which catalyze the incorporation of molecular oxygen in polyunsaturated fatty acids (PUFA) such as linoleic acid forming hydroperoxides or hydroperoxyl fatty acids. To date the role of oxylipin regulation on stomatal immunity is not well-characterized. Linolenic acid and linoleic acid were not altered much in wild-type Arabidopsis, while both decreased dramatically in lox1 mutant upon pathogen infection. In lox1 upon pathogen infection, the lipoxygenase products RES oxylipin 13HPODE was increased, while 9HPODE was decreased. In addition, several metabolites e.g., coumaric acid, ferulic acid, pipecolic acid, and phytohormone melatonin were regulated in oxylipins-mediated stomatal immunity. The bacteria entry assay showed fewer bacteria growth in leaves with the pretreatment of melatonin, and Evans blue and DAB staining showed less oxidative damage in leaves. Exogenous melatonin rescued lox1 defective stomata closure upon pathogen infection. We hypothesize that LOX pathway regulates downstream of melatonin and COR hijack signal cascades are regulated by LOX1 oxidized RES oxylipins. Our results suggest that exogenous melatonin improves stomatal immune responses by directly reducing ROS and alternating expression of genes involved in the metabolisms of phytohormones jasmonic acid and salicylic acid.