| Abiotic stresses such as drought and salt usually lead to the dehydration of plant,thus severely limiting plant growth and development.The high efficiency of water transport is an important factor maintaining the normal growth of plants,and the aquaporins play crucial roles in dominating the transmembrane transport of water by regulating the symplast pathway and water transport in plants.Aquaporins are the member of the major intrinsic proteins,widely present in the plants.They are involved in a variety of plant biological processes,and have positive regulatory roles in response to salt stress.Thellungiella salsuginea is one of the typical halophytes grown in coastal saline soils,and exhibits a strong salt tolerance.In our study,two aquaporins from Thellungiella salsuginea,TsPIP1;1gene and TsTIP1;1 gene,were isolated and transformed to rice,respectively,and the physiological and molecular response profiles of TsPIP1;1 and TsTIP1;1 under salt stress were analysed.TsPIP1;1 gene consists of four exons and three introns,and encodes 284 amino acid residues with855bp length.Protein structural prediction showed that the TsPIP1;1 had six transmembrane helices and contained two NPA motifs and amphiphilic molecular channels,which were specifically present in the MIPs family.RT-PCR analyses showed that the expression of TsPIP1;1 gene in transgenic rice was not affected by salt stress and revealed stable levels.Under salt stress,the physiological measurements showed that the transgenic lines had stronger salt tolerance than the wild type,and also demonstrated the less damage on the growth of transgenic rice comparing to the wild type.The transgenic rice lines could enhance the photosynthetic rates by maintaining the relative stability of chlorophyll content,and increasing stomatal conductance and intercellular CO2 concentration,thus improving the water use efficiency,fresh weight,and grain rates.Futhermore,the transgenic lines had a higher relative water content and water holding capacity though the accumulation of osmolytes and decrease of osmotic potentials in response to salt stress.Determination of Na+and K+contents and NMT results showed that the overexpression of the TsPIP1;1gene in the transgenic rice could maintain the balance of Na+and K+and enhance salt tolerance.The paraffin sections confirmed that the cells of the transgenic line OE-19 are orderly arranged with highly neat and compact styles,and the membrane structures were more complete in response to salt stress.The decrease of MDA content in the transgenic rice also demostrated that overexpression of the TsPIP1;1 gene reduced the damage of salt on the cell membrane and maintained the integrity of cell membrane.The transgenic line OE-19 overexpressing the TsPIP1;1 gene triggered different salt responses,and obviously exhibited differentially expression genes patterns compared with the wild type.Analyses showed that these differentially expressed genes were mainly involved in the biological processes and cell components.KEGG enrichment analysis indicated that DEGs were participated in the process of biological metabolism associated with photosynthesis.Additionally,the line OE-19 also showed multiple transcription factors,protein kinases and functional proteins in differentially expression genes in response to stress.The transgenic rice lines overexpressing TsTIP1;1 and TsPIP1;1 gene demonstrated different response mechanisms under salt stress.The comparison data showed that the transgenic rice overexpressing of the TsTIP1;1 gene maintained the normal growth and improved the salt tolerance by increasing photosynthetic rate and water use efficiency.The overexpression of the TsPIP1;1 in the transgenic rice increased the accumulation of intracellular osmolytes through the regulation of the osmotic potential and water loss rate,and enhanced the water holding capacity of rice and decrease in salt damage on the plant. |
