Differential plant response to toxins and elicitor proteins released by the potato and tomato pathogens Alternaria solani and Alternaria alternata

Abstract

Abstract Early blight of potato and tomato, caused principally by Alternaria solani, results in extensive damage to foliar tissues. Symptoms are seen as expanding necrotic lesions. Lesions are sometimes surrounded by a halo of chlorotic tissue, however the basis for presence or absence of the distinctive halo have not been determined. To dissect the basis for lesion development a series of Alternaria-associated toxins and potential elicitor proteins were tested in potato and tobacco. Infiltration of leaves demonstrated that, while most of the pure toxins did not have a visible effect, two anthraquinones, bostrycin and altersolanon A, elicited a strong necrosis-mediated response. Extracts of solid and liquid cultures of A. solani yielded anthraquinones that also elicited a necrotic response. Two potential elicitor proteins were identified and cloned from the potato brown spot and early blight pathogens Alternaria alternata and A. solani, respectively. Agrobacterium-mediated infiltration and expression of the A. alternata xyloglucanase cel12-A and A. solani Hrip1 revealed that cel12-A had no apparent effect, whereas Hrip1 induced expanding tissue death and development of chlorotic halos. Development of chlorotic halos was dependent on leaf age, with older leaves exhibiting halos. It is proposed that specific toxin and elicitor production, in conjunction with tissue susceptibility mediate the outcomes of early blight symptoms.