Park, Sang-Wook , Kaimoyo, Evans , Mosher, Stephen , Kumar, Dhirendra , Klessig, Daniel F. .
Methyl Salicylate is a Critical Mobile Signal for Plant Systemic Acquired Resistance.
We have previously reported the role of salicylic acid-binding protein 2 (SABP2) of tobacco as an integral component of systemic acquired resistance (SAR); SABP2 is a methyl salicylate (MeSA) esterase that has high affinity for SA which feedback inhibits its esterase activity (Kumar and Klessig PNAS 100:16101; Forouhar et al. PNAS 102:1773). SAR is a state of heightened defense, providing a long-lasting, broad spectrum resistance to pathogens that is activated throughout the plant following a primary infection. SAR requires systemic movement through the phloem of an as-yet unidentified signal molecule from infected tissue to systemic tissue. Results presented here argue that MeSA is a phloem-mobile SAR signal and SABP2 perceives this signal in systemic tissue. Results of grafting studies indicate that SABP2ís MeSA esterase activity, which converts biologically inactive MeSA into active SA, is required in systemic tissue. A mutation, which destroys SABP2ís SA-binding activity and the resulting feedback inhibition leading to unregulated MeSA esterase activity, has no effect on SAR if expressed in systemic tissue but compromises SAR if expressed in primary infected tissue that generates the SAR signal. MeSA levels increase in primary infected leaves, phloem exudates from these leaves and systemic leaves of control plants but not in these tissues of transgenic tobacco expressing the unregulated SABP2. The rise in SA levels in systemic tissue after primary infection of wild-type plants, also is suppressed in these plants expressing its unregulated SABP2, as well as in plants silenced for SABP2 expression. Moreover, treatment of lower leaves of tobacco with MeSA induces SAR in the upper untreated leaves; SABP2 is required in the untreated, but not in the treated, leaves.
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1 - Boyce Thompson Institute for Plant Research, Tower Road, Ithaca, NY, 14850, USA
systemic acquired resistance
salicylic acid-binding protein 2
mobile SAR signal.
Presentation Type: ASPB Minisymposium
Location: Continental A/Hilton
Date: Monday, July 9th, 2007
Time: 9:45 AM