Polygalacturonase Beta-subunit Antisense Gene Expression in Tomato Plants Leads to a Progressive Enhanced Wound Response and Necrosis in Leaves and Abscission of Developing Flowers

Tomato (Lycopersicon esculentum var. Better Boy) plants were transformed with a tomato leaf wound-inducible polygalacturonase (PG) beta-subunit gene in the antisense orientation (PGbetaS-AS) under the control of the cauliflower mosaic virus 35S promoter. The leaves of the transgenic plants exhibited small localized lesions, which eventually enlarged and spread throughout the entire surfaces of the leaves, resulting in cell death. The same lesions were also observed in the peduncle of developing flowers, extending to the whole flower causing abscission, resulting in a sterile phenotype. Leaves of transgenic plants exhibited elevated levels of PG activity, hydrogen peroxide, and enhanced defense signaling in response to wounding and elicitor treatment. The defense signaling increased was accompanied by an increased resistance toward tobacco hornworm (Manduca sexta) larvae. The cumulative results suggest that in the absence of the beta-subunit protein in tomato leaves, an increase in PG activity occurred that led to an enhanced wound response, the formation of lesions leading to severe necrosis, and an abscission of developing flowers.