The roles of salicylic acid-binding protein 2 and methyl salicylate in systemic acquired resistance to TMV in tobacco

• Published in: Phytopathology 2006-06, Vol.96 (6), p.S150-S150
• Main Authors: Park, S-W, Kumar, D, Vlot, A C, Kaimoyo, E, Klessig, D F
• Format: Article
• Language: English
• Subjects: Tobacco mosaic virus
• ISSN: 0031-949X

The salicylic acid-binding protein 2 (SABP2) of tobacco is a methyl salicylate (MeSA) esterase that has high affinity for SA, a critical signal for the activation of plant defenses against pathogens. The 3-D structure of SABP2, alone and in complex with SA, has been determined, confirming that it is a member of the alpha/beta hydrolase superfamily. SA binds in the active site of SABP2, thereby inhibiting its esterase activity. Silencing of SABP2 expression suppresses local resistance to tobacco mosaic virus (TMV) and blocks the development of systemic acquired resistance (SAR). Our recent grafting studies have extended theses findings. We found that SABP2 is required in the systemic tissue to respond to the SAR signal, but is not needed in the infected tissue to generate this signal. Its role is to convert biologically inactive MeSA to active SA in the systemic tissue. At the high levels of SA reached in the infected tissue, SABP2's esterase activity would be inhibited by SA bound in its active site. This feedback inhibition likely facilitates the build up of MeSA, which may serve as a primary (or secondary) phloem-mobile signal for SAR.