Molecular cloning and characterization of wheat calreticulin (CRT) gene involved in drought-stressed responses

Abstract

Calreticulin (CRT) is a highly conserved and ubiquitously expressed Ca(2+)-binding protein in multicellular eukaryotes. CRT plays a crucial role in many cellular processes including Ca(2+) storage and release, protein synthesis, and molecular chaperone activity. To elucidate the function of CRTs in plant responses against drought, a main abiotic stress limiting cereal crop production worldwide, a full-length cDNA encoding calreticulin protein namely TaCRT was isolated from wheat (Triticum aestivum L.). The deduced amino acid sequence of TaCRT shares high homology with other plant CRTs. Phylogenetic analysis indicates that TaCRT cDNA clone encodes a wheat CRT3 isoform. Southern analysis suggests that the wheat genome contains three copies of TaCRT. Subcellular locations of TaCRT were the cytoplasm and nucleus, evidenced by transient expression of GFP fused with TaCRT in onion epidermal cells. Enhanced accumulation of TaCRT transcript was observed in wheat seedlings in response to PEG-induced drought stress. To investigate further whether TaCRT is involved in the drought-stress response, transgenic plants were constructed. Compared to the wild-type and GFP-expressing plants, TaCRT-overexpressing tobacco (Nicotiana benthamiana) plants grew better and exhibited less wilt under the drought stress. Moreover, TaCRT-overexpressing plants exhibited enhanced drought resistance to water deficit, as shown by their capacity to maintain higher WUE (water use efficiency), WRA (water retention ability), RWC (relative water content), and lower MDR (membrane damaging ratio) (P < or = 0.01) under water-stress conditions. In conclusion, a cDNA clone encoding wheat CRT was successfully isolated and the results suggest that TaCRT is involved in the plant response to drought stress, indicating a potential in the transgenic improvements of plant water-stress.

Molecular cloning of a new wheat calreticulin gene TaCRT1 and expression analysis in plant defense responses and abiotic stress resistance

“…Arabidopsis AtCRT3 expression was immediately activated after 30 min of salt treatment, then declined to its original expression level (Persson et al, 2003). Similar expression patterns to AtCRT3 were also found in TaCRT (Jia et al, 2008), OsCRO1 (Arun et al, 2004) and CpCRT (Chen et al, 2005) .In this study, the TaCRT1 was induced by low temperature and infection of CYR32 of Puccinia striiformis. Expression pattern of TaCRT1 after infection by CYR32 was similar to those of the four homologous calreticulin genes mentioned above.…”

“…Through function-known proteins in group I and II, it can be concluded that plant calreticulin protein conserved highly in its structure evolution, but with diversity in biological functions, thus promoting plant adaption abilities to environmental stresses. In addition, AtCRT3 and TaCRT in group III were identified to play roles in plant response to salt and drought stresses respectively (Persson et al, 2003;Jia et al, 2008). TaCRT1, a member of group III, is 97.2% identical to TaCRT, and so it may play certain roles in plant defense responses or stress resistance.…”

“…In Group II, tobacco ACH72686 and papaya CpCRT participate in plant defense responses (Lu et al, 2010;Shen et al, 2010), while tobacco NtRPL60 and caster bean AAB71420 play roles in plant growth and development (Denecke et al, 1995;Coughlan et al, 1997). In Group III, only Arabidopsis AtCRT3 and wheat TaCRT have been demonstrated to function in plant response to salt and drought stress (Persson et al, 2003;Jia et al, 2008). Therefore, the members in each group possess diverse biological functions (Figure 2).…”

“…The rice gene OsCRO1 from CRT family was induced by low temperature as a response mechanism to cold stress (Li et al, 2003). Wheat gene TaCRT enhanced tobacco drought tolerance whereas it was overexpressed in tobacco (Jia et al, 2008). AtCRT3 expression was inducible by high salt treatment (Persson et al, 2003).…”

Cloning and characterization of the calreticulin gene in Asian seabass (Lates calcarifer)

“…A number of functions have been ascribed to the CRT, including Ca 21 sequestration, transcriptional regulation, antithrombotic activity and cell proliferation (Michalak et al, 1999). Recently, it has been proposed to be a molecular chaperone (Kales et al, 2004;Jia et al, 2008), as it has been found to be transiently associated with folding intermediates of glycoprotein. The CRT gene is believed to play a main role as a lectin-like chaperone to viral peptides.…”