Overexpression Of LeHSP21.5 Alleviates The UPR In Tomato And Enhances Their Stress Tolerance

The accumulation of unfolded proteins in the endoplasmic reticulum (ER) lumen causes ER stress response, activates the unfolded protein response (UPR) signal pathway and consequently induces the expression of ER-located molecular chaperones (such as BiP, calnexin, etc.) in eukaryote cells. However, most researches about the function of ER-located molecular chaperones in UPR are only focused on high molecular chaperones, neglecting the small heat shock proteins (sHSPs). The analysis of expressive characterization and sub-cellular localization of LeHSP21.5 revealed that LeHSP21.5 was a typical ER-located small heat shock protein. In order to study its possible role in UPR signaling system, we constructed the eukaryotic expression vector overexpressing LeHSP21.5 and carried out tomato transformation. Transformation lines were generated and used for investigating the UPR response under different stress conditions.The main results were shown as follows:1. Northern and Western blot analyses revealed consistently the heat-inducible character of the LeHSP21.5 gene which possess of a low efficient promoter. No LeHSP21.5 expression was detected after chilling and salt stresses. A single copy of LeHSP21.5 was detected in tomato genome by Southern blot analysis. The similar distribution profile of LeHSP21.5 in microsome fractions of sucrose gradient with the ER marker protein-Calnexin, supported the interpretation that LeHSP21.5 was a small heat shock protein located in the ER.2. We introduced the full length LeHSP21.5 gene under the control of cauliflower mosaic virus 35S promoter into tomato, using an Agrobacterium-mediated transformation. The transgenic tomato plants overexpressing LeHSP21.5 were generated. Southern blot analysis showed that the LeHSP21.5 gene had already been integrated to tomato genome with one copy. Northern blot analysis showed that the LeHSP21.5 gene was constitutively expressed in transgenic tomato plants under normal growth conditions, and the transcripts level of LeHSP21.5 was different among independent transformation lines. It had been...