Abstract：Plant lipoxygenases(LOX) play an important role in plant response to environmental stress, as well as in plant growth and development. A novel LOX gene designated as CaLOX2(GenBank accession number: JQ219046) was isolated using in silico cloning from Capsicum annuum L. and characterized by RT-PCR. The length of the gene was 2 843 bp, which contained a 2 730 bp long open reading frame(ORF), coding a 910 animo acid polypeptide. The deduced amino acid sequence of the gene contained the typical domain of lipoxygenase and putative transit peptides for chloroplast import. Phylogenetic analysis revealed that CaLOX2 clustered together with well-characterized plastidic typeⅡ13-LOXs genes from tomato(Solanum lycopersicum)TomLOXD, potato(Solanum tuberosum) StLOXH3 and tobacco(Nicotiana attenuate) NaLOX3. Real-time quantitative PCR analysis showed that CaLOX2 transcripts were expressed in all tissues of pepper, however the expression patterns of the gene had tissue specificity，the transcripts were most abundantly expressed in the leaf but much less in flower; the expression level of the CaLOX2 mRNA could be up-regulated significantly after inoculation with zoospores of Phytophthora capsici in both incompatible and compatible interaction. But, its expression level was much higher and earlier at time point in the incompatible interaction than that in the compatible interaction., which indicated CaLOX2 was involed in race-specific resistance to Phytophthora capsici in pepper. The gene expression patterns differed in different pepper organs, its expression level was much higher but later at time point in the leaves than that in the roots after inoculated with Phytophthora capsici race ph1. The expression of CaLOX2 was up-regulated after treatment with mechanical wounding and NaCl stress, but down-regulated by low temperature. This gene was highly induced by H2O2, salicylic acid (SA), and methy jasmonic acid (MeJA). The comparison of CaLOX2 with the well-studied LOXs from other plant species in phylogenetic analysis and expression patterns indicated that the most likely biochemical function of CaLOX2 was in the biosynthesis of JA through allene oxide synthase(AOS) pathway but not in the hydroperoxide lyase mediated (HPL-mediated) production of C6-aldehydes. These results indicated that CaLOX2 is probably involved in the disease resistance and defense response to Phytophthara capsici and other environment stress，such as low temperature and high salt, through SA and JA pathways. The study may provide basic information for further functional analysis of the genes involved in resistance to Phytophthara capsici and other environmental stress in pepper.
