Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2007
Publication Date: 5/7/2007
Citation: Mozoruk, J.J., Hunnicutt, L.E., Hunter, W.B., Bausher, M.G. 2008. CsV03-3 is a member of a novel gene family from citrus that encodes a protein with DNA binding activity and whose expression is responsive to defense signals and abiotic stress. Journal of Plant Physiology. 165(5):531-543. Interpretive Summary: Plants are exposed to wide array of stressful challenges not only in their natural environment but also when cultivated for agricultural use. The recent outbreak of citrus canker and citrus greening in Florida gives impetus to study mechanisms underlying pathogen and insect resistance in non-model species such as Citrus sinensis. A better understanding of the interplay between how a stress is perceived and how a defense response is mounted will be crucial for the development of optimized crop protection strategies that augment or increase the effectiveness of the citrus defensive mechanisms through molecular breeding and transgenic methods. The research presented here aims to decipher and understand the molecular mechanisms of inducible defense by studying its underlying genetic basis. To this end, we have discovered and begun to characterize a novel family of stress responsive genes from orange. This work will increase our understanding of how defense mechanisms against stress challenges are perceived and/or mounted in orange.
Technical Abstract: We have identified a novel gene designated CsV03-3 from Citrus sinensis (L.) Osbeck that encodes a 50 amino acid polypeptide with a predicted molecular mass of 5.4 kDa and a pI of 3.7. CsV03-3 expression is up-regulated by application of methyl jasmonate, salicylic acid, and abscisic acid as well as by abiotic stress and insect herbivory. CsV03-3 belongs to a small gene family consisting of at least three other closely related members (CsV03-1, CsV03-2, CsV03-4) whose expression is also responsive to phytohormone pathways and abiotic stress. Sequence similarity searches of the public databases were unsuccessful in finding sequence homologs to CsV03-3 or any CsV03 family member; however, structural prediction models coupled with model comparison with Protein Data Bank folds indicated that the predicted polypeptide of CsV03-3 has structural similarity to proteins with nucleic acid binding activity. Gel mobility shift assays performed on recombinant CsV03-3 protein demonstrated active binding with dsDNA and, to a lesser extent, ssDNA. Based on the phytohormone inducible expression patterns, the ability to bind nucleic acids and the lack of significant sequence homology, we propose that CsV03-3 and its related homologs defines a new class of nucleic acid binding proteins that are responsive to defense and stress signaling in woody perennials.