IDENTIFICATION AND CHARACTERIZATION OF GENES REQUIRED FOR CHILLING TOLERANCE IN ARABIDOPSIS
Smith, Gracen Ann
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Chilling tolerance describes the ability of a plant to grow and reproduce in low, but non-freezing, temperatures between 2°C to 12°C. Many important agricultural crops that evolved in warm climates lack the mechanisms to withstand chilling stress. As we lack knowledge regarding genetic control of these chilling tolerance mechanisms, the model plant Arabidopsis thaliana, a chilling-tolerant plant, has often been used successfully to better identify and the molecular mechanisms required for survival at low temperature. To identify genes required for chilling tolerance in Arabidopsis I obtained large pools of insertional mutation lines and screened them for the development of chilling injuries. Using a phenomics approach to screen for decreases in photosynthetic efficiency at low temperature I identified five mutant lines with confirmed chilling symptoms. One of these lines had a mutation in KONJAC2, which codes for an enzyme known to act in L-ascorbic acid synthesis. L-ascorbic acid acts as a redox buffer in chilling. In a low temperature screen of confirmed homozygous insertional mutant lines I identified and characterized a role in chilling for two additional genes. One of the lines identified had a T-DNA, At4g03410, which produced an overexpression of unknown function. This overexpression resulted in chilling injury in the plant, whereas another line producing a knock-down of the gene produced a slight benefit in chilling over wild type. Due to the phenotype, I called this gene SENSITIVE when OVEREXPRESSED at LOW-TEMPERATURE (SOL). Another line that developed chilling injury at low temperature had an insertion in PRIORITY IN SWEET LIFE 4 (PSL4), the β-subunit of the ER resident glucosidase II required for proper N-glycosylation of proteins. Genetic and biochemical approaches suggested that the transcription factor LOS2 was N-glycosylated at 2°C in wild-type plants but not in the psl4-2 mutant, hindering the proper control of chilling responsive transcripts controlled by LOS2 and ZAT10, the transcription factor that acts between LOS2 and low-temperature responsive genes. These results reveal new roles in chilling tolerance for three genes, two of which had previously known regulatory functions in optimal growth conditions but no known roles in low temperature survival.