Characterization of the Low-Temperature Response of EARLI1 in Arabidopsis

One approach toward understanding adaptation of plants to their environment is to investigate environmental regulation of gene expression. Our focus is on the environmental regulation of EARLI, which is activated by cold and long-day photoperiods. Cold activation of EARLII in short-day photoperiods is slow, requiring several hours at 4°C before an increase in mRNA abundance can be detected. EARLII is not efficiently cold-activated in etiolated seedlings, suggesting that photomorphogenesis is necessary for its cold activation. Cold activation of EARLII is inhibited in the presence of the calcium channel blocker lanthanum chloride or the calcium chelator EGT A. Addition of the calcium ionophore Bay K8644 results in cold-independent activation of EARLII. These data suggest that EARLII is not an immediate target of the cold response, and that calcium flux affects its expression. EARLII is a putative secreted protein and has motifs found in lipid transfer proteins. Overexpression of EARLII in transgenic plants has no effect upon flowering time but did result in reduced electrolyte leakage during freezing damage, suggesting that EARLII may affect membrane or cell wall stability in response to low temperature stress. In addition a cold acclimated transgenic line carrying an RNAi construct designed to knockout EARLII and possibly three of its family members, shows greater leakage than wild type-acclimated plants at -6 and -8° C. The regulation of EARLII was reconstituted using promoter: :GUS fusions in transgenic plants to determine the minimal DNA fragment that responds to cold shock. A 100bp region between -1183 and -I085 appears to be sufficient to confer low-temperature induction upon a reporter gene, as assayed by northern hybridization. Within this region are two putative Myc and one Myb trariscription factor binding sites