VuNIP1 (NOD26-like) and VuHSP17.7 gene expression are regulated in response to heat stress in cowpea nodule

In tropical areas, high soil temperatures frequently limit biological nitrogen fixation (BNF) activity in a number of legumes species. In contrast with other legumes growing under BNF, cowpea (Vigna unguiculata) nodules are very resistant to high-temperature stress. However, the molecular basis of nodule heat tolerance remains unclear. In order to identify genes involved in the heat stress response in cowpea nodules a cDNA library was screened with cDNA-AFLP derived probes. Two full-length cDNAs corresponding to a small heat shock protein (VuHSP17.7) and to a Nodulin 26 (VuNIP1) were isolated and characterized. VuHSP17.7 encodes a sHSP family class I protein, and VuNIP1 corresponds to a NOD26-like protein, member of NIP subfamily of plant membrane intrinsic protein (MIP). VuHSP17.7 was highly induced by high-temperature stress in nodule, leaves, flower, and bud flower, and VuNIP1 was repressed in nodule after heat stress. Moreover, the spatial expression pattern of VuNIP1 and VuHSP17.7 differs significantly indicating that distinct signaling pathways under heat stress may regulate the expression of these genes.     

昆虫的热休克反应和热休克蛋白

热休克（热激heatshock）是指短暂、迅速地向高温转换所诱导出的一种固定的应激反应。诱导该反应的温度在种与种之间有所不同。热休克反应最明显的特征是：伴随着正常蛋白质合成的抑制,一部分特殊蛋白质的诱导和表达增加,即为热休克蛋白（heatshockproteins,HSPs）。尽管热休克蛋白的合成也能被其它形式的应激反应所诱导,将它们认为是应激蛋白可能更恰当,但人们习惯上仍将这类蛋白质称为热休克蛋白。由于热休克反应和热休克蛋白是在果蝇（Drosophiliamelanogaster）中最初发现的,故在昆虫中,特别是果蝇等双翅目昆虫中研究得较深入…     

Heat shock induces changes in the expression and binding of ubiquitin in senescent Drosophila melanogaster

We examined the effect of aging on the expression of ubiquitin RNA and the binding of the ubiquitin polypeptide to proteins following heat shock in Drosophila melanogaster. Heat-shocked adult flies transcribe two major RNA species-one of 4.4 kb and one of about 6 kb that hybridize to the polyubiquitin-encoding probe. Several less abundant RNAs were also observed but the 4.4-kb band was present as the major RNA species in both stressed and nonstressed flies of both ages. The 6-kb fragment was more abundant in heat shocked aged flies than in younger flies. The quantitative expression of the polyubiquitin gene increased in proportion to the duration of the heat stress. Moreover, the induction of the polyubiquitin RNA was markedly elevated during aging following heat shock. Hybridization of Northern blots with the monoubiquitin gene probe revealed a band of 0.9 kb that was not significantly affected by heat stress. We also investigated the relationship between the changes in polyubiquitin gene expression and the formation of ubiquitin-protein complexes in aging heat-shocked flies. Heat shock to old flies results in a significant increase in the level of proteins immunoprecipitated by anti-ubiquitin antibodies. In the case of proteins synthesized 2 h before heat shock, most of the ubiquitinated proteins were of high molecular weight. For those proteins synthesized during a 30-min heat shock and the 2 h following heat shock, two major immunoprecipitated bands were observed: an 80-kD and a 70-kD polypeptide. The ubiquitination of a 60 kD protein was also observed in nonstressed flies, but its for mation was drastically reduced following heat shock. For proteins synthesized during and after heat shock from both age groups, the major ubiquitinated polypeptide is 70 kD. In all age groups, more ubiquitin complexes were formed with proteins synthesized before heat shock, than with proteins synthesized either during or after heat shock. This suggests that cellular proteins synthesized at physiological temperatures are more sensitive to heat induced damage than those synthesized during stress. These data support the hypothesis that in aging flies, heat shock induces an unusually high concentration of abnormal proteins which are targeted for degradation by the ubiquitin-dependent proteolytic system. © 1993Wiley-Liss, Inc.