Down-regulated gene expression of cold acclimated Poncirus trifoliata

Abstract

Citrus sp. are important commercial fruit crops throughout the world that are occasionally devastated by subfreezing temperatures. Poncirus trifoliata (maximum freeze tolerance of -26°C) is a close relative of commercial Citrus sp. (maximum freeze tolerance of -10°C) that has been used in breeding programs to develop more cold-hardy genotypes and as a rootstock to enhance freeze tolerance of the scion. Species with greater freeze tolerance vary in gene expression during cold acclimating temperatures. mRNA differential display (DDRT-PCR) and quantitative relative RT-PCR were used to study down regulation of gene expression in intact P. trifoliata exposed to a gradual cold acclimation regime to enhance our understanding of the mechanism that makes this specie so freeze tolerant. Six down-regulated genes were isolated and sequenced. These down-regulated genes showed high homology to the following known genes: chlorophyll a/b binding protein, photosystem II OEC 23, carbonic anhydrase, tumor related protein, pyrrolidone-carboxylate peptid ase and β-galactosidase. Photoprotection and the global control of gene expression related to photosynthesis appear to be important mechanisms for cold acclimation of P. trifoliata. Key words: Differential display, down-regulated genes, Poncirus trifoliata, cold acclimation and quantitative relative RT-PCR