Defence gene expression and the effects of leaf age and day length on the nonhost resistance of Arabidopsis to the cowpea rust fungus

Mutant and transgenic Arabidopsis thaliana plants deficient in defence signalling pathways were grown under 16 h days and used to demonstrate that the nonhost resistance of this species to the cowpea rust fungus required the presence of the salicylic acid signalling pathway. Under these conditions, resistance was affected by leaf age and associated with the expression of PR (pathogenesis-related) genes 2 and 5, but not PR-1, plant defensin 1.2 and basic-chitinase. However, data from wildtype plants grown under different day lengths suggested that PR-2 and PR-5 expression may not be the main factors contributing to nonhost resistance in this system.