Identification and characterization of potato protease inhibitors able to inhibit pathogenicity and growth of Botrytis cinerea

Different tissues of potato, tobacco, and bean plants were screened for anti-fungal protease inhibitor (PI) activity, also following fungal pathogen inoculation or mechanical wounding. A potato (Solanum tuberosum var. Desireé) sprout protein extract showed a strong inhibitory activity against chymotrypsin and Botrytis cinerea fungal proteases, but also on spore germination, hyphal elongation, and development of necrotic lesions. An active mixture of different proteins was affinity column purified and sequenced. Two new anti-fungal genes, PKI1 and PPI3B2, coding, respectively, for a Kunitz-type inhibitor and a Proteinase Inhibitor 1 capable of reducing fungal lesion development, were cloned and partially characterized. Direct effect on leaf necrosis formation was found to be dependent on the anti-chymotrypsin activity of both selected inhibitors. The PKI1 transcript was found to accumulate in untreated sprout tissues, although homologues of this gene seemed to accumulate following Bemisia tabaci attack. In the case of PPI3B2, we provide preliminary evidence that a member of the Proteinase Inhibitor 1 family is active against not only herbivorous insects but also phytopathogenic fungi and foliar lesions caused by them.