Molecular cloning of a novel pathogen-inducible cDNA encoding a putative acyl-CoA synthetase from Capsicum annuum L.

By means of differential display, a pool of salicylic acid (SA)-induced mRN As were identified and subsequently their cDNAs were isolated from a cDNA l ibrary prepared from SA-induced leaf tissues of hot pepper. One of these cD NA clones, designated CaSIG4, was 1900 bp and contained an open reading fra me encoding 523 amino acids with a calculated molecular mass of 56.3 kDa. T he predicted amino acid sequence of CaSIG4 showed high sequence similarity to the AMP-binding protein family of both prokaryotic and eukaryotic acyl-C oA synthetases. CaSIG4 transcripts accumulated rapidly after SA treatment a nd in response to both incompatible and compatible interactions with Xantho monas campestris pv. vesicatoria race 1. To investigate the cis-acting elem ents mediating CaSIG4 expression, the CaSIG4 5'-flanking region was isolate d by inverse PCR. Database searches indicated that a potential cis-regulato ry element is almost identical to the consensus core sequences ACC(A/T)ACC( A/C) which are conserved among promoters of other phenylpropanoid biosynthe tic genes. The subcellular localization of the CaSIG4 protein was studied b y using a soluble modified GFP gene fusion delivered into epidermal cells o f onion by biolistic bombardment. The CaSIG4-smGFP fusion protein was local ized to the plasma membrane. Taken together, CaSIG4 encoding a putative acy l-CoA synthetase could function as a plasma membrane-bound protein with a r ole in signaling in plant defense.