In Vitro Interaction of Nuclear Proteins with the Promoter of Soybean Heat Shock Gene Gmhsp17.5E

Transcriptomic Analysis of the Interaction Between FLOWERING LOCUS T Induction and Photoperiodic Signaling in Response to Spaceflight

Spaceflight has an impact on the growth and development of higher plants at both the vegetative stage and reproductive stage. A great deal of information has been available on the vegetative stage in space, but relatively little is known about the influence of spaceflight on plants at the reproductive stage. In this study, we constructed transgenic Arabidopsis thaliana plants expressing the flowering control gene, FLOWERING LOCUS T (FT), together with the green fluorescent protein gene (GFP) under control of a heat shock-inducible promoter (HSP17.4), by which we induced FT expression inflight through remote controlling heat shock (HS) treatment. Inflight photography data showed that induction of FT expression in transgenic plants in space under non-inductive short-day conditions could promote flowering and reduce the length of the inflorescence stem in comparison with that of wild-type plants under the same conditions. Whole-genome microarray analysis of gene expression changes in leaves of wild-type and these transgenic plants grown under the long-day and short-day photoperiod conditions in space indicated that the function of the photoperiod-related spaceflight responsive genes is mainly involved in protein synthesis and post-translation protein modulation, notably protein phosphorylation. In addition, changes of the circadian component of gene expression in response to spaceflight under different photoperiods indicated that roles of the circadian oscillator could act as integrators of spaceflight response and photoperiodic signals in Arabidopsis plants grown in space.

Isolation and characterization of six heat shock transcription factor cDNA clones from soybean

Thermal stress in soybean seedlings causes the activation of pre-existing heat shock transcription factor proteins (HSFs). Activation results in the induction of DNA binding activity which leads to the transcription of heat shock genes. From a soybean cDNA library we have isolated cDNA clones corresponding to six HSF genes. Two HSF genes are expressed constitutively at the transcriptional level, and the remaining four are heat-inducible. Two of the heat inducible genes are also responsive to cadmium stress. Comparative analysis of HSF sequences indicated higher conservation of the DNA binding domain among plant HSFs than those from yeast or other higher eukaryotes. The putative plant HSF oligomerization domain contains hydrophobic heptapeptide repeats characteristic of coiled coils and seems to exist in two structural variants. The carboxy-terminal domains are reduced in size and the C-terminal heptad repeat is degenerate.

AT-rich promoter elements of soybean heat shock gene Gmhsp17.5E bind two distinct sets of nuclear proteins in vitro

A 33 bp double-stranded oligonucleotide homologous to two AT-rich sequences located upstream (-907 to -889 and -843 to -826) to the start of transcription of heat shock gene Gmhsp17.5E of soybean stimulated transcription when placed 5' to a truncated (-140) maize Adh1 promoter. The chimeric promoter was assayed in vivo utilizing anaerobically stressed sunflower tumors transformed by a pTi-based vector of Agrobacterium tumefaciens. Nuclear proteins extracted from soybean plumules were shown to bind double-stranded oligonucleotides homologous to AT-rich sequences in the 5' flanking regions of soybean beta-conglycinin, lectin, leghemoglobin and heat shock genes. These proteins were also shown to bind AT-rich probes homologous to homeobox protein binding sites from the Antennapedia and engrailed/fushi tarazu genes of Drosophila. Binding activity specific for AT-rich sequences showed a wide distribution among various plant organs and species. Preliminary characterization indicated that two sets of nuclear proteins from soybean bind AT-rich DNA sequences: a diverse high-molecular-weight (ca. 46-69 kDa) group, and a low-molecular-weight (23 and 32 kDa) group of proteins. The latter meets the operational criteria for high-mobility group proteins (HMGs).

Mutational analysis of a plant heat shock element

A total of 32 mutations were generated within the TATA-proximal site 1 (-72 to -47) of soybean heat shock gene Gmhsp17.5E in order to functionally define the optimal configuration of sequences within the heat shock element (HSE). Mutants were tested in vivo utilizing sunflower tumors transformed by a T-DNA based vector. Promoter activity was determined by S1 nuclease hybrid protection analysis of tumor transcripts. A total of five repeats (5'-nGAAn-3' or 5'-nTTCn-3') which comprise the HSE at site 1 were required for full transcription induction by heat stress. Analysis of non-conserved bases flanking the central trinucleotide block indicated that 5'-aGAAg'-3' is the optimum sequence for the 5 bp repeat.

Isolation and analysis of the expression of two genes for the 81-kilodalton heat-shock proteins from Arabidopsis

We have cloned and characterized two members of the family of genes for the 81-kilodalton heat-shock proteins from Arabidopsis thaliana, HSP81-1 and HSP81-2. Comparison of the entire genomic sequence of the HSP81-1 gene with the corresponding full-length cDNA previously reported as AtHS83 (TW Conner, PR LaFayette, RT Nagao, JL Key [1990] Plant Physiol 94: 1689-1695) reveals the presence of three introns of 315, 83, and 88 base pairs. By contrast, analysis of the HSP81-2 genomic and partial cDNA sequences suggests that the HSP81-2 gene is interrupted by only two introns of 304 and 106 base pairs. The 5'-initiation sites of the two corresponding mRNAs were mapped from results of experiments with S1 nuclease. The deduced amino acid sequences of the proteins encoded by these two genes show 88% identity, and they also show striking similarities to the hsp90 family of proteins in yeast and animal cells. From the results of northern blot analysis of transcripts, it appears that the expression of the HSP81-1 gene occurs at only very low levels in the absence of heat shock and is strongly induced by heat (35 degrees C). The HSP81-2 gene is constitutively expressed at much higher levels, and its expression is moderately enhanced by elevated temperatures. Severe heat shock appears to block the splicing of the pre-mRNA transcribed from HSP81-1. We also examined the effects of arsenite and cadmium on the expression of the HSP81 genes, as well as on other groups of hsp genes in Arabidopsis. Treatment with cadmium was marginally effective in inducing hsp genes, whereas arsenite stress strongly stimulated the accumulation of each mRNA in a coordinated fashion.

Synergistic effect of upstream sequences, CCAAT box elements, and HSE sequences for enhanced expression of chimaeric heat shock genes in transgenic tobacco

The thermoregulated expression of the soybean heat shock (hs) gene Gmhsp17.3-B is regulated via the heat shock promoter elements (HSEs), but full promoter activity requires additional sequences located upstream of the HSE-containing region. Structural features within this putative enhancer region include a run of simple sequences which are also present upstream of HSE-like sequences of other soybean hs genes, and three perfect CCAAT box sequences located immediately upstream from the most distal HSE of the promoter. A series of heterologous and homologous promoter fusions linked to the chloramphenicol acetyl transferase (CAT) gene was constructed and examined in transgenic tobacco plants. The region containing the AT-rich domain of the 5' flanking region was unable to direct transcription from the TATA box of a truncated delta CaMV35S promoter. Heat-inducible CAT activity was detectable when additional sequences from the native promoter containing three CCAAT boxes and a single HSE were present in the constructions. Complete reconstitution of the native hs promoter/enhancer region increased hs specific CAT activities only very little, but deletion of CCAAT box sequences reduced CAT expression five-fold. Our results suggest that AT-rich sequences have a moderate effect on thermoinducible expression levels of the soybean heat shock gene and that CCAAT box sequences act cooperatively with HSEs to increase the hs promoter activity.