Identification and Analysis of Cold Stress-inducible Genes in Korean Rapeseed Varieties

The rapeseed plant (Brassica napus) is one of the top five oil-producing crops in the world. However, its potential for global cultivation is limited due to its sensitivity to cold. We selected five varieties of rapeseed popular in Korea and analyzed their sensitivity to cold stress. Three - 'Naehan', 'Sandongchae', and 'Yudal' - proved more tolerant than the other two - 'Youngsan' and 'Tammi'. Because rapeseed is in the same family (Brassicacae) as Arabidopsis, one would expect that both share similar genes, with protein coding sequences that show >86% homology. We used a cDNA microarray enriched with Arabidopsis cold stress-related genes to examine the molecular background for differences in sensitivity among rapeseed varieties. Their hierarchical clustering patterns for expression were highly correlated with their cold-sensitive phenotypes. For example, expression patterns were similar between 'Naehan' and 'Sandongchae' as well as between 'Yudal' and our Arabidopsis samples. Using co-expression gene sets developed in this laboratory, we further analyzed expression patterns for three cultivars. Three distinct gene sets were commonly enriched in 'Naehan' against 'Youngsan' and 'Tammi', indicating that they could be the core gene sets that confer a high degree of cold tolerance in 'Naehan'. Knockout plants with down-regulated expression of GSTF2, TRXh5, LTI30, and LACS4 were highly cold-sensitive whereas overexpression of those four genes led to a reversal of this sensitivity. In fact, overexpression of GSTF2 and LTI30 enhanced tolerance, with plants that over-expressed GSTF2 having extremely high tolerance that enabled them to acclimate almost completely to freezing conditions. By comparison, only about 40% of the wild type demonstrated a similar acclimation. Therefore, the genes described here could be useful in furthering our knowledge about other stress responses in rapeseed, thereby facilitating the production of cold-tolerant plants.