Barcala Marta, García Alejandra, Cubas Pilar, Almoguera Concepción, Jordano Juan, Fenoll Carmen, Escobar Carolina
Facultad de Ciencias del Medio Ambiente, Universidad de Castilla-La Mancha, Campus de la Real Fábrica de Armas, 45071 Toledo, Spain.
Plant Mol Biol. 2008 Jan;66(1-2):151-64. doi: 10.1007/s11103-007-9259-3. Epub 2007 Nov 28.
Genes coding small heat-shock proteins (sHSPs) show distinct behaviours with respect to environmental and developmental signals. Their transcriptional regulation depends on particular combinations of heat stress cis-elements (heat-shock elements; HSEs) but many aspects regarding their regulation remain unclear. Cyst and root-knot nematodes induce, in the roots of infected plants, the differentiation of special feeding cells with high metabolic activity (syncytia and giant cells, respectively), a process accompanied by extensive gene expression changes. The Hahsp17.7G4 (G4) promoter was active in giant cells and its HSE arrangements were crucial for this activation. In the present work, we provide further basis to associate giant cell expression with the heat-shock response of this gene class, by analysing additional promoters. The Hahsp17.6G1 (G1) promoter, not induced by heat shock, was silent in giant cells, while Hahsp18.6G2 (G2), which responds to heat shock, was specifically induced in giant cells. In addition, a mutated Hahsp17.7G4 promoter version (G4MutP) with a strong heat-shock induction was also induced in giant cells. The responses of the different promoters correlated with distinct HSE configurations, which might have implications on differential trans-activation. Furthermore, the shortest giant cell and heat-shock-inducible sHSP promoter version analysed in tobacco (-83pb Hahsp17.7G4) fully maintained its expression profile in Arabidopsis. Cyst nematodes did not induce the Hahsp17.7G4 promoter, revealing additional specificity in the nematode response. These findings, together with the fact that the class I sHSP products of endogenous genes accumulated specifically in tobacco giant cells, support the idea that these nematode-induced giant cells represent a transcriptional state very similar to that produced by heat shock regarding this class of genes. The high metabolic rate of giant cells may result in unfolded proteins requiring class I sHSPs as chaperones, which might, somehow, mimic heat-shock and/or other stress responses.
编码小分子热休克蛋白（sHSPs）的基因在环境信号和发育信号方面表现出不同的行为。它们的转录调控取决于热应激顺式元件（热休克元件；HSEs）的特定组合，但关于其调控的许多方面仍不清楚。胞囊线虫和根结线虫会在受感染植物的根中诱导具有高代谢活性的特殊取食细胞（分别为多核细胞和巨型细胞）的分化，这一过程伴随着广泛的基因表达变化。Hahsp17.7G4（G4）启动子在巨型细胞中具有活性，其HSE排列对这种激活至关重要。在本研究中，我们通过分析其他启动子，为将巨型细胞表达与该基因类别的热休克反应联系起来提供了进一步的依据。Hahsp17.6G1（G1）启动子不受热休克诱导，在巨型细胞中沉默，而对热休克有反应的Hahsp18.6G2（G2）在巨型细胞中被特异性诱导。此外，具有强烈热休克诱导作用的突变型Hahsp17.7G4启动子版本（G4MutP）在巨型细胞中也被诱导。不同启动子的反应与不同的HSE构型相关，这可能对差异反式激活有影响。此外，在烟草中分析的最短的巨型细胞和热休克诱导型sHSP启动子版本（-83pb Hahsp17.7G4）在拟南芥中完全保持其表达谱。胞囊线虫不会诱导Hahsp17.7G4启动子，这揭示了线虫反应中的额外特异性。这些发现，连同内源性基因的I类sHSP产物在烟草巨型细胞中特异性积累这一事实，支持了这样一种观点，即这些线虫诱导的巨型细胞在这类基因方面代表了一种与热休克产生的转录状态非常相似的状态。巨型细胞的高代谢率可能导致未折叠蛋白需要I类sHSP作为伴侣蛋白，这可能以某种方式模拟热休克和/或其他应激反应。
