Spontaneous lesions and HR in transgenic plants overexpressing the wild-type and mutant Pto transgenes. Northern blot shows the accumulation of transgene transcripts in primary transgenic plants. Non-transgenic PtoS plants were used as a control. Lines 104, 160, 345, 93, 124, 135, 455, 456, 458, and 471 carrying respective transgenes were examined in the T2 generation for the presence (+) or absence (−) of visible spontaneous lesions (SL) in leaves without infection. The plants were also tested for the presence (+) or absence (−) of HR in response to P. s. pv tomato (avrPto).