ALTERATION OF BETA-TUBULIN GENE-EXPRESSION DURING LOW-TEMPERATURE EXPOSURE IN LEAVES OF ARABIDOPSIS-THALIANA

Responses of beta-tubulin gene expression to low-temperature exposure (4-degrees-C) have been investigated in leaves of Arabidopsis thaliana. During low-temperature exposure, the patterns of both alpha- and beta-tubulin isoforms are altered; the effect is smaller for the alpha-tubulins than for the beta-tubulins, however. An examination of beta-tubulin gene expression revealed that during low-temperature exposure, transcript levels of TUB2, TUB3, TUB6, and TUB8 decrease, whereas those of TUB4, TUB5, and TUB7 remain constant, and the TUB9 transcript level increases. The changes in transcript levels of TUB6, TUB8, and TUB9 were detectable after 6 h of low-temperature treatment. As shown by transcription-blocking experiments, the in vivo decay rates at 25-degrees-C are comparable to those at 4-degrees-C for TUB5, TUB6, and TUB8 mRNAs, whereas TUB9 mRNA appears to be more stable at 4-degrees-C than at 25-degrees-C. Thus, decreases in transcript levels of TUB6 and TUB8 in response to low temperature appear to be regulated at the transcriptional level, and the increase in TUB9 transcript level that results from lowering the temperature from 25-degrees-C to 4-degrees-C may be due in part to its slower rate of decay at 4-degrees-C. When a chimeric gene containing 1061 base pairs of TUB8 5' flanking DNA fused to the beta-glucuronidase coding region was used to produce transgenic Arabidopsis plants, the chimeric gene expression was down-regulated in response to low temperature as assayed by histochemical localization and RNA gel blots. These results confirm that the alteration of transcript levels of TUB8 in response to low temperature is regulated at the transcriptional level.