| Our laboratory is using the Brassica oleracea-Xanthomonas campestris pv. campestris (XCC) model system to investigate the physiological and molecular aspects of defense gene regulation. Because one of our primary goals is the cloning of specific defense related genes, we have constructed a cDNA library, from Hancock variety cabbage, and screened it with various probes in order to isolate and identify genes which may be involved in the defense responses of Brassica oleracea. As a result of this screening we have isolated several clones, one of which showed particular promise during our initial screening analysis. This clone, designated NPS45, is highly homologous to putative translation initiation factors of the eIF1/SUI1 gene family. Some translation initiation factors such as, eIF2 and eIF4, have been shown to act as regulators of gene expression. Recent research suggests that other factors, including eIF1, may also be involved in translational regulation.;The objective of our work is to characterize the expression patterns of the putative translation initiation factor, NPS45, in response to XCC and various other stresses. To examine the role that NPS45 might play in defense responses, we inoculated resistant and susceptible Brassica oleracea varieties with XCC. In addition to this we also examined the expression of this gene in plants treated with salicylic acid and jasmonic acid. We also examined the expression of this gene during plant development, wounding and thermal stress.;We were unable to make any specific correlation between the expression of NPS45 and disease resistance. The expression of NPS45 varied greatly among varieties tested and no distinctive pattern of expression was observed. Further characterization is needed before we can make a conclusive statement about the role of NPS45 in the defense responses of Brassica oleracea. We were, however, able to observe a distinct pattern of expression in Brassica plants exposed to thermal stress. In heat stressed plants the expression of NPS45 is greatly decreased in plants exposed to prolonged periods of heat stress. In cold stressed plants the expression of NPS45 first decreases and then increases during prolonged exposure to cold temperatures. Our results illustrate the complexity of translational mechanisms of regulation. Further research into the expression of translation initiation factors in response to physiological stresses will help to elucidate the specific mechanisms that underlie this type of regulation. |
