A novel, conditional, lesion mimic phenotype in cotton cotyledons due to the expression of an endochitinase gene from...

We have observed a novel, lesion mimic phenotype (LMP) in the cotyledons of cotton seedlings expressing an endochitinase gene from Trichoderma virens. This phenotype, however, is conditional and is elicited only when the transgenic seedlings are germinating on a medium that is devoid of mineral nutrients. The LMP manifests itself around the 5th day in the form of scattered, dry necrotic lesions on the cotyledons. The severity of the LMP is correlated with the level of transgene activity. Production of reactive oxygen species and activities of certain defense related enzymes and genes were substantially higher in the cotyledons of seedlings that were growing under mineral nutrient stress. Molecular and biochemical analyses indicated significantly higher-level activities of certain defense-related genes/enzymes at the onset of the phenotype. Treatment with methyl jasmonate can induce LMP in the cotyledons of wild-type (WT) seedlings similar to that observed in the endochitinase-expressing seedlings grown on nutrient-free medium. On the other hand, salicylic acid (SA), its functional analog, benzo(1,2,3) thiadiazole-7-carbothioic acid (BTH), and ibuprofen can rescue the LMP induced by the seedling-growth on nutrient-deficient medium. Nutrient deficiency-induced activation of a defense response appears to be the contributing factor in the development of LMP in endochitinase-expressing cotton seedlings.