| Soil saline-alkalinity shows significant constraints to crop productivity. Alkaline soil has high pH, which showed easy to harden, poor permeability and low fertility. The effect of soil alkalinization on plants resulting from NaHCO3 and Na2CO3 may be more destructive than the effect of soil salinization induced by the accumulation of neutral salts. The plant response to salinity stress has been exhaustively researched, but much less attention has been paid to analyze the mechanism of soil alkalinity on plant growth and development. It’s urgent to analyze the mechanism of plant tolerance to alkalinity, especially for crops.1. SR4 was a suitable material for studying the mechanism of alkalinity and identifying tolerance related genes.SR4 is a derivative of an asymmetric somatic hybridization involving as parents the wheat cultivar Jinan 177 (JN177) and tall wheatgrass (Thinopyrum ponticum 2n=70). In our research, yield index of SR4 and control wheat varieties in different saline-alkali land and saline-alkali pool were analyzed. In 2013, growth performance of SR4 and another salt resistance somatic hybrid introgression cultivar SR3 was much better than that of JN177 in saline-alkali land of Dongying. Moreover, growth performance of SR4 was also much better than that of salt resistance control cultivar DK961 in Weifang. In 2014, the yield of SR4 showed an increase of 15.0% and 35.4% when compared with SR3 and JN177 respectively, in saline-alkali land of Kenli, Dongying city. In addition, the yield of SR4 showed an increase of 18.6% and 42.4% when compared with SR3 and JN177 respectively, in saline-alkali land of Gudao, Dongying city. In saline-alkali pool, the yield of SR4 was still higher than that of JN177 and SR3. These results showed that SR4 could maintain higher yield under alkaline stress, which indicated that SR4 had higher tolerance to alkaline stress.2. Next-generation sequencing-based transcriptome profiling analysis of wheat alkaline stress-related genes in rootThe seedling growth of both SR4 and JN177 was inhibited under alkaline stress, but the inhibition effect was greater on JN177. SR4 maintained a higher level of proline content, higher reactive oxygen species (ROS) scavenging enzyme activities, lower Na+/K+ ratio and malondialdehyde (MDA) content. High-throught Illumina sequencing was used to analyze the differently expressed genes in JN177 and SR4 under control and alkaline stress for both 0.5 h and 24 h. A total of 2,814,938 unfiltered tags were recovered from the six libraries, reduced to 1,229,902 after filtering. Following mapping to the reference sequences,123,730 unigenes were recognized. The GO categories over-represented in both wheat cultivars were much similar, with most represent for metabolism of different compounds, response to stress and iron transport. A number of genes involved in nutrient ions transporters, controlling both intracellular and rhizosphere pH, ROS scavenging processes and epigenetic modification were induced in SR4, which may contribute to the tolerance of SR4 to alkaline stress.3. An Aux/IAA protein gene TaIAA10 enhanced tolerance to alkalinityThrough screening the wheat alkaline stress responsive genes, we found an auxin responsive gene TaIAA10, which expressed differently in SR4 and JN177 under alkalinity. Previous studies showed that auxin could reduce the inhibition of alkalinity on plant, but little was known about the exact mechanism. We compared the growth of SR4 under control condition, alkalinity stressed condition and also alkalinity accompanied with auxin, and found that auxin alleviated the inhibitory effect of alkalinity to SR4. TaIAA10 overexpression lines were generated in wheat (OX) and Arabidopsis (OE). Under alkaline stress, the non-transgenic wheat seedlings exhibited serious wilting and yellow leaves, whereas the OX lines showed green leaves and longer roots compared with the non-transgenic control wheat. After treatment with alkaline pH and NaHCO3, no difference was observed in seed germination rate between OE and wild type Col-0, however, the growth of OE was much better than that of Col-0 at post-germination stage. In the seedling stage, the relative growth rate of primary root and the growth of leaves were also better in OE than wild type Col-0 under alkaline treatment. These results indicated that overexpression of TalAA10 enhanced the tolerance of plants to alkaline stress.4. An Aux/IAA protein gene TaIAA10 influenced plant developmentTaIAA10 mainly localized in the nucleus and included four conserved domains characterized in other Aux/IAA proteins. TaIAA10 had orthologues in Gramineaes such as Brachypodium distachyon, rice, sorghum and maize. Overexpression of TaIAA10 in Arabidopsis thaliana didn’t influence seed germination rate, but inhibited the growth of cotyledons and roots after germination. However, the hypocotyls of OE lines were longer than that of wild type. Moreover, shoot of OX lines, hypocotyl and root of OE lines losed gravitropic responses. Lateral root formation was also inhibited in OE compared with the wild type. The expression of A/LBD29 was lower in overexpession lines, which may account for the inhibition of lateral root formation.In comparison with Col-0, the hypocotyl length of OE was longer under white light and was shorter under dark, far-red or blue light, indicating that TaIAA10 participated in photomorphogenesis.5. TaIAA10 improved abiotic stress tolerance by ABA biosynthetic and signaling pathwayThe OE lines showed more tolerant to ABA at post-germination stage and in seedling growth. Further analysis showed that the expressions of AtNCED3 involved in ABA synthesis and that of AtMYC2, AtRD29B and AtRAB18 involved in abiotic stress responsive pathways were induced in OE lines, while the expression of AtABI3, AtABI4 and AtABI5 were markedly reduced in OE lines. The OE lines also showed tolerance to osmotic and oxidative stress compared with Col-0. The expressions of AtAPX2 and AtSOD were found to be increased in OE lines. The phenotype of OE under ABA treatment was more obvious and the expression of genes involved in ABA signaling parthway were much more changed than the other two stress treatments, thus, TaIAA10 may improve tolerance to abiotic stress by promoting ABA biosynthetic and signaling pathway. |
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