Comparative Study On Roteomics Between Salt And Drought Stress Of An Introgression Line Of Wheat

At the present time, environment is becoming worse and worse, which has harmful impact on agricultural productivity around the world. In all, the useable lands for cultivation are less than 10%, the great mass of lands are in drought, salinity, quagmire and cold. Therefore, it is an important task to dissect the mechanisms of salt and drought adaptive plants with the aim to cultivate new salt and drought tolerant varieties.In our group, a new wheat variety, Shanrong No. 3 (SR3), with high salt/drought tolerance and high yield was successfully bred via asymmetric somatic hybridization between wheat (Triticum aestivum L. cv. Jinan177 (JN177) and Thinopyrum ponticum. This novel cultivar is an introgression line containing chromatin of Thinopyrum ponticum. In this study, a proteomic study was conducted to determine the difference in young root and leaf proteomes of SR3 and its somatic hybrid parent JN177. Differences in proteomics response of the hybrid and the parent between drought and salt stress were analysed. RT-PCR assay was used to analyse the transcription patterns of 25 selected differentially expressed proteins. Taken together, responsive characteristics of SR3 and JN177 under salt/drought stress were systematically investigated at transcriptional and translational levels, and the mechanism of salt/drought resistance is discussed:1. In total, 93 differentially expressed proteins were obtained in roots of JN177 and SR3 seedlings under drought and salt stress. Of them, eighty-eight were identified by MALDI TOF-TOF MS. First, root proteome of SR3 was markedly different from that of JN177. Results showed that thirteen spots were special to SR3 and 21 spots were particular to JN177. Second, significant difference was there in expression patterns of salt/drought-induced proteins between SR3 and JN177. Among the 20 salt/drought-induced proteins, three were specific to SR3 and five were specific to JN177, the others were induced in both of them. Third, there were distinguishing differences in expression patterns between salt- and drought-responsive proteins. Compared with drought stress, Up-regulated and down-regulated proteins under salt stress were increased by 19.2% and 11.7% respectively. This suggested that salt stress could bring harder and broader stress responsive processes and changed the expression patterns of more proteins than drought stress. The other proteins such as quinone reductase (root 90) and eukaryotic translation initiation factor 5A3 (root 74) were down-regulated under drought stress but inhibited under salt stress in roots of JN177 suggested that there were some difference in signal transduction pathways between salt and drought stress. Fourth, there were variety-differences in expression patterns of salt/drought stress responsive proteins between SR3 and JN177, and it was shown that expression patterns of the same protein were different between JN177 and SR3. For instance, nucleotide-excision repair protein (root 21) was down-expressed in JN177 but unchanged in SR3 under salt/drought stress; Aldolase (root 8) was unchanged in JN177 but up-regulated in SR3 under drought stress; eukaryotic translation initiation factor 5A3 (root 74) was inhibited in JN177 but down-regulated in SR3. It was the somatic hybridization that changed the expression patterns of stress responsive proteins.2. Sixty-five differentially expressed proteins were found in leaves of JN177 and SR3 seedlings under salt and drought stress, 63 ones were identified by MALDI TOF-TOF MS. Comparative analysis showed that the state was similar to roots. For example, there were also remarkable differences in expression patterns between salt-and drought-responsive proteins in leaves: chlorophyll a/b-binding apoprotein CP24 precursor (leaf 1) was increased by 12.7 times under drought stress in SR3 whereas increased by 6.1 times under salt stress; Expression of catalase (leaf 23) was inhibited under salt stress in JN177; superoxide dismutase (leaf 51) was up-regulated under drought stress whereas unchanged under salt stress. This reflected the difference in the signal transduction pathways between salt and drought stress. Furthermore, obvious differences were there in expression patterns between SR3 and JN177 in leaves: such as chlorophyll a/b-binding apoprotein CP24 precursor (leaf 1) was down-regulated in leaves of JN177 whereas increased in that of SR3 under salt/drought stress, 2-Cys peroxiredoxin-like protein (leaf 21) was up-regulated in SR3 whereas unchanged in JN177 under drought stress, expression of catalase (leaf 23) was inhibited in JN177 whereas increased in SR3 under salt stress. But differences in proteomes of leaves between JN77 and SR3 were not so marked as in those of roots; differences between JN177 and SR3 in leaves were smaller than in roots, among 14 salt/drought-induced proteins, one was specific to SR3, the others were induced in both of them under salt and drought stress.3. Twenty-eight proteins (including 25 differentially expressed proteins in root 2-D map and SOS 1/2/3 which tied up with salt stress) were selected for RT-PCR assay. Results indicated that: 1) transcription patterns of encoding sequences of 17 selected proteins under salt/drought stress were different from those under control condition except for 11 proteins whose expression patterns were identical between salt/drought stress and control. It showed that transcription and translation are relatively independent processes and there are no direct relationships between the characteristics of expression patterns of stress responsive proteins in transcriptional and translational level, their expressions under salt/drought stress are comprehensively regulated at different levels. 2) At transcription level, no proteins were found with variety-specific whereas in proteomes of root and leaf, many variety-specific proteins existed. Hereby, regulations of variety-specific proteins were carried out at post-transcriptional level; somatic hybridization inhibited the transcriptions of some mRNA and activated the transcriptions of some mRNA which could not transcript originally. 3) The percentage of proteins with changed transcription patterns under salt stress were higher than those under drought stress (increased by 7.1-14.3% in roots and 28.6%-32.2% in leaves, respectively). We suggested that salt stress can bring broader stress responsive processes and changed the transcription patterns of more proteins than drought stress. This case was the same to the proteomes.4. Significant difference between root and leaf proteomes under salt/drought stress was found. 1) A remarkable difference was the photosynthesis associated proteins which was the biggest group (25.81%) in leaf but not found in root. The other three chloroplast proteins were identified in roots: Transketolase, chloroplast (root 4), Ferredoxin-nitrite reductase, chloroplast precursor (root 29), Glutamine synthetase leaf isozyme, chloroplast precursor (root) 45. Functions of them in roots need further study. 2) Antioxidants in roots and leaves were different significantly. Six and one antioxidants were found in roots and leaves of SR3 respectively, whereas in JN177, three were found in roots and none in leaves. It showed that antioxidant ability was stronger in root than in leave, and antioxidant ability of SR3 was more powerful than JN177. 3). Transporting associated proteins of roots were different from that of leaves. Six transporting associated proteins were identified in roots whereas three in leaves. Vacuolar proton ATPase subunit E (root 70) and putative potassium channel beta subunit (root 86) detected in root are of great importance in maintenance of vacuolar proton homeostasis and ion transportation. This showed that root played important role in salt/drought resistance than leaf.5. Somatic hybridization affect greatly on the proteome of wheat: 1) Somatic hybridization impacted the expression of proteins in chloroplasts and mitochondria; 2) In comparison with JN177, expression of some proteins was inhibited whereas some new proteins were synthesized, as well as post-translational modifications of some proteins occurred in SR3. 3) Somatic hybridization changed the expression patterns of some stress-related proteins: such as dehydroascorbate reductase (root 38) up-regulated for 20.3 times in JN177 but not expressed in SR3 under drought stress; whereas under salt stress, expressions were up-regulated for 14 and 25.1 times in J 77 and SR3 respectively. Catalase (leaf 23) was up-regulated for 7.8 times in SR3 but not changed in JN177 under drought stress; whereas under salt stress, expression was up-regulated for 9.4 times in SR3 but not expressed in JN177.According to the above results and analysis, we can conclude as follows:1) Somatic hybridization significantly changed the root and leaf proteomes and transcriptomes of wheat seedlings, and made the systems of the photosynthesis, energy synthesis, antioxidants and proton homeostasis of SR3 more effective than its parent, JN177. It was the systematic change that enhanced the salt/drought resistance controlled by multiple genes of the hybrid.2) Signal transduction pathways of salt and drought stress are largely identical but with minor differences, not only at proteome level but also at transcription level. This was shown by some stress responsive proteins with different expression patterns between salt and drought stress.3) Compared with root and leaf proteomes, root was found to be more important than leaf under salt/drought stress, thus root proteome is more accurate than that of leaf to reflect the salt and drought resistance of plants.