Information concerning genes and signals regulating cold acclimation processes in plants is abundant; however, less is known about genes and signals regulating the deacclimation process. A population of primarily winter B. napus varieties was used to conduct a genome-wide association study and to compare the transcriptomes from two winter B. napus varieties showing time-dependent differences in response to cold acclimation and deacclimation treatments. These studies helped to identify loci, candidate genes, and signaling processes impacting deacclimation in B. napus. GWAS identified polymorphisms at five different loci associated with freezing tolerance following deacclimation. Local linkage decay rates near these polymorphisms identified 38 possible candidate genes. Several of these genes have been reported as differentially regulated by cold stress in arabidopsis (Arabidopsis thaliana), including a calcium-binding EF-hand family protein (encoded by BnaCnng10250D) that was also differentially expressed during deacclimation in this study. Thousands of other genes differentially expressed during the acclimation and deacclimation treatments implicated processes involving oxidative stress, photosynthesis, light-regulated diurnal responses, and growth regulation. Generally, responses observed during acclimation were reversed within one week of deacclimation. The primary differences between the two winter B. napus varieties with differential deacclimation responses involved protection from oxidative stress and the ability to maintain photosynthesis.

Winter canola can tolerate temperatures below -10°C for short periods of time if first cold acclimated. However, fully cold acclimated plants can deacclimated and lose this ability if exposed to temperature above 10°C for as little as three days. Multi-day warm spells in early winter and late spring are occurring more frequently due to climate resulting in damage and yield loss when freezing temperatures reoccur. We have phenotyped a previously genotyped diversity panel of 430 winter canola lines that demonstrate variation in deacclimation rates and have identified 4 loci that were associated with differential deacclimation responses. Ten potential candidate genes within the QTLs observed were identified and two independent arabidopsis mutants for each gene were obtained. We developed methods to quantify freezing tolerance in unacclimated acclimated, and deacclimated plants. Both arabidopsis lines with mutations in VERNALIZATION INDEPENDENCE 3 (VIP3) and also both lines with mutations in PHYTOCHROME KINASE SUBSTRATE 4 (PSK4) altered freezing tolerance in unacclimated and/or deacclimated plants but had little impact on survival of acclimated plants. Additionally, we determined that deacclimation in canola varied between varieties with most varieties deacclimating completely within three days at 15C but varied at 10C with some lines fully deacclimating, and others only partial deacclimating- even if deacclimated for more than two weeks. We expect these studies to identify mechanisms underlying deacclimation processes in canola and arabidopsis. Winter canola can tolerate temperatures below -10°C for short periods of time if first cold acclimated. However, fully cold acclimated plants can deacclimated and lose this ability if exposed to temperature above 10°C for as little as three days. Multi-day warm spells in early winter and late spring are occurring more frequently due to climate resulting in damage and yield loss when freezing temperatures reoccur. We have phenotyped a previously genotyped diversity panel of 430 winter canola lines that demonstrate variation in deacclimation rates and have identified 4 loci that were associated with differential deacclimation responses. Ten potential candidate genes within the QTLs observed were identified and two independent arabidopsis mutants for each gene were obtained. We developed methods to quantify freezing tolerance in unacclimated acclimated, and deacclimated plants. Both arabidopsis lines with mutations in VERNALIZATION INDEPENDENCE 3 (VIP3) and also both lines with mutations in PHYTOCHROME KINASE SUBSTRATE 4 (PSK4) altered freezing tolerance in unacclimated and/or deacclimated plants but had little impact on survival of acclimated plants. Additionally, we determined that deacclimation in canola varied between varieties with most varieties deacclimating completely within three days at 15C but varied at 10C with some lines fully deacclimating, and others only partial deacclimating- even if deacclimated for more than two weeks. We expect these studies to identify mechanisms underlying deacclimation processes in canola and arabidopsis.