A frameshift in the coding region of a novel tomato class I basic chitinase gene makes it a pseudogene with a functional wound-responsive promoter

A putative class I basic chitinase gene, assigned as ψBCH, was cloned from a tomato breeding line NC 24E. The gene contains a coding region with two introns. The predicted ψBCH open reading frame (ORF) is 971 bp and exhibits 81–88% identity at the nucleotide level with known class I basic chitinase genes from the Solanaceae family. However, the presence of a stop codon caused by a frameshift in the ORF of ψBCH makes it unusual among the other class I plant basic chitinases. This stop codon might be involved in the lower accumulation of fully spliced ψBCH RNA caused by nonsense-mediated decay (NMD), which is an RNA surveillance system universally found in eukaryotes. Sequence analysis of the 1883-bp 5′-flanking region of the ψBCH gene revealed the presence of potential wound-response promoter elements. To study the transcriptional regulation of the ψBCH gene, its 5′-flanking region containing the putative promoter was fused to the gus reporter gene and introduced into the tobacco genome via Agrobacterium tumefaciens-mediated transformation. Transgenic plants were functionally assayed for β-glucuronidase activity. The ψBCH promoter drives the reporter gene expression in response to wounding stimuli. ψBCH promoter-GUS analysis indicates that wound-response of the tobacco transgene was rapid and localized in the wounded area following mechanical wounding. Therefore, our results suggest that the ψBCH promoter can provide targeted expression of genes, such as protease inhibitors in response to pest attack.