Analysis Of Gene Expression In Roots Tissue Of Tamarix Hispida In Response To NaHCO₃Stress

Tamarix plants, which include shrubs or small trees, are widely distributed in drought-stricken areas and in salinic soil in Central Asia and Western of China. Tamarix plants are highly tolerant to different abiotic stresses including drought, salinity and high temperatures, thus making them ideal plants to aid reversing environmental degradation. These characteristics make them also valuable for the study of mechanisms of stress resistance.To investigate stress responses in plant roots, four transcriptomes from roots of Tamarix hispida treated with NaHC03for0,12,24and48h were built using Solexa technology. In total,81,344unigenes were generated. There were3,976,6,057and3,069genes significantly differentially expressed after stress for12,24and48h, respectively. The dynamic changes in the differentially expressed genes (DEGs) and their relationship to stress were identified. Ten clusters of genes were found to be significantly co-expressed. GO-enriched analysis showed that the processes of cellular protection, protection and repair of damaged structural proteins, signal pathway responses to stress, and maintaining and re-establishing cellular ion homeostasis may play major roles in the stress tolerance of T. hispida. We examined15transcriptional factor (TF) families from the transcriptomes, including Myb, Myc, bZIP, ERF, WRKY, NAC, ABRE, DREB, bHLH, and MADS Box. These TF families contained1605unique TF genes. DGE analysis showed that the largest numbers of TFs were differentially expressed at24h, followed by12and48h. Under NaHCO3stress, genes involved in proline and trehalose synthesis were highly induced, suggesting that proline and trehalose levels were highly increased in T. hispida. Fifty heat shock proteins (45%in total) were DEGs, suggesting important roles in stress tolerance. Novel genes accounted for a high percentage (32.7%-50.5%) of total DEGs, indicating their importance for an in-depth characterization of stress tolerance mechanisms. This systematic analysis has identified several stress response genes pivotal for an in-depth characterization of stress tolerance mechanisms in plants.In this study, we cloned14unique LTPs genes (ThLTP1-14) from T. hispida to investigate their roles under various abiotic stress conditions. The expression profiles of the14ThLTPs in response to various abiotic stresses and abscisic acid (ABA) exposure in root, stem and leaf tissues were investigated using real time RT-PCR. The results showed that all14ThLTPs were expressed in root, stem and leaf tissue under normal growth conditions. However, under normal growth conditions, ThLTP abundance varied from each organ, with expression differences of9000-fold in leaves,540-fold in stems, and3700-fold in roots. These results indicated that activity and/or physiological importance of these ThLTPs are quite different. Differential expression of the14ThLTPs and18ThAQPs were observed (>2-fold) for NaCl, PEG, NaHCO3and CdCl2in at least one tissue indicating they were all involved in abiotic stress responses. All ThAQPs were highly induced (>2-fold) under ABA treatment in roots, stems and/or leaves, and suggesting they are regulated by the ABA signal transduction pathway. In addition, ThAQPs were more highly induced in roots than in stem and leaf tissues, indicating that these genes may play roles in stress responses mainly in the roots rather than the stem and leaves. We hypothesize that ThLTPs and ThAQPs expression constitutes an adaptive response to abiotic stresses in T. hispida and plays an important role in abiotic stress tolerance.To investigate the expression pattern of ThAQP11, the promoter of ThAQPll was isolated using TAIL-PCR approach. The obtained promoter sequence is1605bp in length and contains some stress-response cis-acting elements such as MYB, MYC, WRKY, ABRE and so on. The promoter of ThAQP11was inserted into a plant expression vector pCAMBIA1301to replace CaMV35S promoter (PAQ11:GUS). The Arabidopsis seedlings tansformed with PAQ11: GUS were obtained. The histochemical GUS staining analysis showed that the ThAQP11mainly expressed in cotyledon, leaf veins and taproot.To screen the upstream regulatory genes of ThAQP11promoter using yeast one-hybrid, a bZIP transcription factor binding to cis-element ABRE was obtained. The results indicated that the bZIP can regulate the expression of ThAQP11through interaction with the cis-acting elements ABRE under abiotic stresses.