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 bet a-tubulin isoforms are altered; the effect is smaller for the alpha-tu bulins than for the beta-tubulins, however. An examination of beta-tub ulin gene expression revealed that during low-temperature exposure, tr anscript 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 w ere detectable after 6 h of low-temperature treatment. As shown by tra nscription-blocking experiments, the in vivo decay rates at 25-degrees -C are comparable to those at 4-degrees-C for TUB5, TUB6, and TUB8 mRN As, 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 i n response to low temperature appear to be regulated at the transcript ional level, and the increase in TUB9 transcript level that results fr om lowering the temperature from 25-degrees-C to 4-degrees-C may be du e 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 b eta-glucuronidase coding region was used to produce transgenic Arabido psis plants, the chimeric gene expression was down-regulated in respon se to low temperature as assayed by histochemical localization and RNA gel blots. These results confirm that the alteration of transcript le vels of TUB8 in response to low temperature is regulated at the transc riptional level.