2,6-DICHLOROISONICOTINIC ACID-INDUCED RESISTANCE TO PATHOGENS WITHOUTTHE ACCUMULATION OF SALICYLIC-ACID

Systemic acquired resistance (SAR) is a pathogen-inducible defense mec hanism effective against a wide range of pathogens. Salicylic acid (SA ) is an essential component of this pathway, as transgenic plants unab le to accumulate salicylic acid are incapable of developing SAR. Here, we show that the synthetic chemical 2,6-dichloroisonicotinic acid (IN A) acts via the SAR signal transduction pathway. However, it does not induce SA accumulation during the time required for the induction of S AR gene expression or resistance to TMV. Furthermore, INA can induce b oth resistance and SAR gene expression in transgenic tobacco and Arabi dopsis plants that cannot accumulate SA. Thus, INA apparently activate s a component of the SAR signaling pathway downstream of SA accumulati on.