Induction of pepper cDNA encoding a lipid transfer protein during the resistance response to tobacco mosaic virus

Pepper (Capsicum annuum) plants exhibit hypersensitive response (HR) against infection by many tobamoviruses. A clone encoding a putative nonspecific lipid transfer protein (CaLTP1) was isolated by differential screening of a cDNA library from resistant pepper leaves when inoculated with tobacco mosaic virus (TMV) pathotype P0. The predicted amino acid sequence of CaLTP1 is highly similar to that of the other plant LTPs. Southern blot analysis showed that a small gene family of LTP-related sequences was present in the pepper genome. Transcripts homologous to CaLTP1 accumulated abundantly in old leaves and flowers. CaLTP1 expression was induced in the incompatible interaction with TMV-P0 but was not induced in the compatible interaction with TMV-P1.2. In correlation with the temporal progression of HR in the inoculated leaves, CaLTP1 transcripts started to accumulate at 24 h after TMV-P0 inoculation, reaching a maximal level at 48 h. A strain of Xanthomonas campestris pv. vesicatoria (Xcv) that carries the bacterial avirulence gene, avrBs2, was infiltrated into leaves of a pepper cultivar containing the Bs2 resistance gene. A marked induction of CaLTP1 expression was observed in Xcv-infiltrated leaves. Effects of exogenously applied abiotic elicitors on CaLTP1 expression were also examined. Salicylic acid caused a rapid accumulation of CaLTP1 transcripts in pepper leaves and ethephon treatment also induced the expression of the CaLTP1 gene. Transient expression in the detached pepper leaves by biolistic gene bombardment indicated that CaLTP1 is localized mostly at the plant cell surface, possibly in the cell wall. These results suggest possible role(s) for LTPs in plant defense against pathogens including viruses.