Abstract: Products of plant resistance (R) genes Pto and Cf contain distinct domains, and have different cellular localization. It is intriguing to compare the development mechanisms of resistance conferred by the two R genes. In the present report, two hypersensitive response (HR) initiation systems were employed to study the time course expression induced by Avr/Cf interaction of the genes encoding Pti4, Pti5 and Pti6 which interact directly with Pto: (1) Seeds of tomato (Lycopersicon esculentum Mill.) containing complementary gene pairs Avr4/Cf 4 and Avr9/Cf9 were obtained through crossing. Their seedlings developed HR under room temperature. (2) Avr/Cf seedlings grew normally at 33℃. When the temperature was shifted down to 25℃, HR occurred within hours in the seedlings. Results of both experiments showed that expression of Pti4, Pti5 and Pti6 was induced upon development of hypersensitive necrosis in Avr/Cf seedlings. However, the expression levels and patterns of these Ptis differed. This finding indicated that these Ptis function complementarily, and might be involved in regulation of both Pto and Cf conferred resistance.

Key words: Pti, Cf, hypersensitive response, resistance