Identification of genes associated with cold acclimation in perennial ryegrass.

Cold acclimation dramatically increases freezing tolerance in many temperate plant species. An understanding of cold acclimation is important for extending adaptation areas of perennial ryegrass. Freezing tolerance is greatly increased in perennial ryegrass cv. 'Caddyshack' after cold acclimation. Genes differentially regulated during cold acclimation were identified by analyzing the abundance of expressed sequence tags (ESTs) randomly sampled from two cDNA libraries, one constructed from 14-d cold-acclimated (CA; LT(50)=-12.2 degrees C) and the other from nonacclimated (NA; LT(50)=-7.6 degrees C) leaves of 'Caddyshack'. More than 1400 quality ESTs were generated for each library. Over 60 EST groups were either increased or decreased three times or more in the CA library than in the NA library. Functional classification showed that for nine gene ontology (GO) subcategories, the ratio of CA ESTs to NA ESTs increased twice or more, whereas the ratio decreased by half or more for seven other GO subcategories. Expression analysis of 23 selected genes confirmed that 19 of them exhibited expression patterns consistent with the EST abundance analysis. Our results suggest that up-regulation of cold-regulated (COR), dehydration-responsive, and ice recrystallization inhibition (IRI) genes, and down-regulation of photosynthesis and respiration-related genes are important to increasing freezing tolerance in perennial ryegrass.