ABSTRACT
Transcriptional activity of a 573-bp fragment of HSP101 (At1g74310) incorporated into a Mutator-like element (MULE) transposon was investigated in Arabidopsis thaliana Columbia. Sequence identity between the HSP101-MULE arrangement and a continuous segment of the original HSP101 promoter, 5' UTR exon, and open reading frame (ORF) was high (87%) but lower in the 5' UTR intron (69%). Collectively, the HSP101 ORF, the MULE 5' terminal inverted repeat (TIR), and the 1.3 kb immediately upstream of the TIR is located on chromosome IV, and we refer to it as HSP101B. Located within the HSP101B promoter, upstream of 2 heat shock elements (HSEs), are 4 COR15a-like low-temperature response elements (LTREs). The HSP101B ORF was transcribed in the leaves and influorescences of high-temperature stress (HTS) treated Arabidopsis thaliana but not in low-temperature stress (LTS) and control plants. Transiently transformed Arabidopsis seedlings, as well as stable transformed lines of Linum usitatissimum (flax) and Brassica napus (canola) containing a HSP101B promoter:GUS construct, showed either LTS-, or LTS- and HTS-, induced beta-glucuronidase expression. Results from PCR amplifications of HpaII- and MspI-digested Arabidopsis genomic DNA suggest that endogenous expression of HSP101B may be downregulated by partial methylation of the HSP101B sequence between the TIRs of the associated MULE.
Subject(s)
Arabidopsis/genetics , Cold Temperature , DNA Transposable Elements , Gene Expression Regulation, Plant/physiology , Hot Temperature , Mutagenesis , Plant Proteins/biosynthesis , Plant Proteins/genetics , Promoter Regions, Genetic , Transcription Factors/biosynthesis , Transcription Factors/genetics , Arabidopsis/metabolism , Base Sequence , DNA Transposable Elements/genetics , Flax/genetics , Flax/metabolism , Flowers/genetics , Flowers/metabolism , Molecular Sequence Data , Plant Leaves/genetics , Plant Leaves/metabolism , Plants, Genetically Modified/metabolismABSTRACT
High temperature stress (HTS), during flowering, decreases seed production in many plants. To determine the effect of a moderate HTS on flowering, fruit and seed set in Brassica napus, plants were exposed to a HTS (8/16 h dark/light, 18 degrees C night, ramped at 2 degrees C h-1, over 6 h, to 35 degrees C for 4 h, ramped at 2 degrees C h-1 back to 23 degrees C for 6 h) for 1 or 2 weeks after the initiation of flowering. Although flowering on the HTS-treated plants, during both the 1 week and 2 week HTS treatments, was equal to that of control-grown plants, fruit and seed development, as well as seed weight, were significantly reduced. Under HTS, flowers either developed into seedless, parthenocarpic fruit or aborted on the stem. At the cessation of the HTS, plants compensated for the lack of fruit and seed production by increasing the number of lateral inflorescences produced. During the HTS, pollen viability and germinability were slightly reduced. In vitro pollen tube growth at 35 degrees C, from both control pollen and pollen developed under a HTS, appeared abnormal, however, in vivo tube growth to the micropyle appeared normal. Reciprocal pollination of HTS or control pistils with HTS or control pollen indicated that the combined effects of HTS on both micro- and megagametophytes was required to knock out fruit and seed development. Expression profiles for a subset of HEAT SHOCK PROTEINs (HSP101, HSP70, HSP17.6) showed that both micro- and megagametophytes were thermosensitive despite HTS-induced expression from these genes.
