Cloning of a Zinc-binding Cysteine Proteinase Inhibitor in Citrus Vascular Tissue

Abstract

<jats:p>A partial cDNA (<jats:italic>cvzbp-1</jats:italic>) was cloned based on the N-terminal sequence of a citrus (<jats:italic>Citrus</jats:italic> L.) vascular Zn-binding protein (CVZBP) previously isolated from vascular tissue (Taylor et al., 2002). CVZBP has homology to the Kunitz soybean proteinase inhibitor (KSPI) family. Recombinant protein produced using the cDNA clone inhibited the cysteine proteinase, papain. Metal binding capacity has not been reported for any other member of this family. CVZBP was present in leaves, stems, and roots but not seeds of all citrus species examined. However, CVZBP was present in germinating seeds after the cotyledons had turned green. Within four hrs after wounding, CVZBP was undetectable in the wounded leaf and adjacent leaves. It has been suggested that many members of the KSPI family serve a function in defense. However, the expression of the CVZBP is in direct contrast with those of KSPI members that were implicated in defense response. Though systemically regulated during wounding, we suggest that CVZBP is not a defense protein but rather may function in vascular development.</jats:p>

Differential Expression of Candidate Defense Genes of Poplars in Response to Aphid Feeding

“…PIs comprise at least 10 distinct protein families classiÞed by their amino acid sequence and the mechanistic class of proteinases they inhibit (serine, cysteine, aspartic, and metalloproteases) (Ryan 1990, Jongsma and Bolter 1997, Koiwa et al 1997. PIs take part in regulating endogenous proteinases during germination and development of xylem cells, and they can function as storage proteins (Ellis andTaylor 2004, Jimenez et al 2008) and signaling molecules in plantÐ microbe interactions (Djordjevic et al 2007). PIs play a potent defensive role against insects and pathogens (Major and Constabel 2008), and they have been associated with response to abiotic stress conditions as water deÞcit (Downing et al 1992) or mechanical wounding (Christopher et al 2004).…”