LOW-TEMPERATURE REGULATES ARABIDOPSIS LHCB GENE-EXPRESSION IN A LIGHT-INDEPENDENT MANNER

Low temperature treatment of dark-grown seedlings of Arabidopsis thali ana results in a rapid increase in the amount of mRNAs encoding for th e major polypeptides of the light-harvesting complex of photosystem II (Lhcb1 genes). This increase is transient and seems to be due mainly to the accumulation of Lhcb13 transcripts, indicating that low temper ature differentially regulates the expression of the Arabidopsis Lhcb1 gene family in the dark. A 1.34 kb fragment of the Lhcb13 promoter i s sufficient to confer low temperature regulation to a reporter gene i n transgenic Arabidopsis etiolated seedlings, suggesting that the regu lation is occurring at the transcriptional level. The cold-induced acc umulation of Lhcb13 mRNA is not part of a general response to stressf ul conditions since no accumulation is detected in response to water s tress, anaerobiosis or salt stress. The amount of Lhcb13 mRNA decreas e in response to exogenous abscisic acid (ABA) suggesting that this ph ytohormone acts as a negative regulator. Moreover, the accumulation of Lhcb13 mRNAs in cold-treated ABA deficient etiolated seedlings is hi gher than that of wild-type and ABA insensitive etiolated seedlings, i ndicating that low temperature regulation of Lhcb13 is not mediated b y ABA.