| Prunus mongolica Maxim, which is widely established in the southern Mongolian plateau, shows extreme tolerance to drought. However, there is a lack of available drought resistance mechanisms, especially the molecular mechanism for this species related to its response to water deficiency. Additionally, the presence of mycorrhizae improved the drought tolerance of P. mongolica, but the molecular mechanism for this improvement remains poorly understood. In this paper, to investigate the mechanisms that allow P. mongolica to maintain growth in extremely arid environments, the response of non-mycorrhizal P. mongolica seedlings to drought stress was analyzed using morphological, physiological, biochemical and high-throughput sequencing approaches. Then the mycorrhizal P. mongolica seedlings were selected for applying the same water treatment and culture condition, and harvested at the same time for the high-throughput sequencing. The transcriptome of these 2 treatments seedlings combined with the RNA-seq data of 2 treatments non-mycorrhizal P. mongolica seedlings and the physiolog-biochemical mechanisms of mycorrhizal P. mongolica seedlings in the previous research can reveale the drought resistance mechanism of mycorrhizal P. mongolica at the molecular level. The research results indicated that:(1) We generated 28,713,735 and 26,650,133 raw reads from no-stress control and drought-stressed P. mongolica seedlings, respectively. In total, we obtained 67,352 transcripts with an average length of 874.44 bp. Compared with the no-stress control, 3,365 transcripts were differentially expressed in the drought-stressed seedlings, including 55.75%(1,876 transcripts) up-regulated and 44.25%(1,489 transcripts) down-regulated transcripts.(2) The photosynthesis response showed a decreasing tendency under drought stress, but the changes in the levels of hormones (auxins, cytokinins and abscisic acid) resulted in the closing of stomata and decreased cell enlargement and division; these changes were effective for promoting P. mongolica survival in Gobi Desert.(3) Next, we analyzed the aquaporin and superoxide dismutase gene families due to their importance in plant resistance to drought stress. We found that all of the plasma membrane intrinsic protein transcripts were down-regulated in the drought-stressed treatment, whereas drought did not affect the expression of nodulin intrinsic protein or small basic intrinsic protein transcripts in P. mongolica seedlings. In addition, activation of iron superoxide dismutase transcription and enhanced transcription of manganese superoxide dismutase were observed in P. mongolica to promote tolerance of drought stress.(4) After the next generation sequencing for the 2 mycorrhizal treatments seedlings and re-assembly the transcriptomic data of 2 non-mycorrhizal libraries.43631 transcripts were obtained from 4 libraries. Compared with the mycorrhizal well-watered seedlings, 820 transcripts were differentially expressed in the mycorrhizal drought-stressed seedlings on the premise of p value threshold is 0.001, including 738 up-regulated and 82 down-regulated transcripts; Compared with the drought-stressed seedlings,3751 transcripts were differentially expressed in the mycorrhizal drought-stressed seedlings, including 2208 up-regulated and 1543 down-regulated transcripts; Compared with the well-watered seedlings,2315 transcripts were differentially expressed in the mycorrhizal well-watered seedlings, including 867 up-regulated and 1448 down-regulated transcripts.(5) The enriched analysis results of DETs related KEGG pathway, including ①the formation of mycorrhizae mainly increased the stability of PS Ⅱ system under the drought condition for maintaining a relatively high photosynthetic rate; the synthesis metabolism of organic macromolecular such as starch were increased at the same time, these are the reasons why the biomass of mycorrhizal P. mongolica was increased compared to the non-mycorrhizal P. mongolica seedlings;In addition, the formation of mycorrhiza increased the expression of genes related to C4 fixed pathway in P. mongolica, this is the reason why mycorrhiza improve the water use efficiency P. mongolica under the drought condition. ② The direct reason of mycorrhizal P. mongolica’s ABA contents further increased was the P. mongolica increased the synthesis of ABA under the dark condition after incoluated the Funneliformis mosseae; additionally, the formation of mycorrhizae also promoted the biosynthesis of auxin, zeatin and brassinosteroids, these hormones combined impact on the P. mongolica, make it better response to drought stress. ③ The N, P uptake of P. mongolica were mainly depended on the mycorrhizal pathway when P. mongolica associated with the Funneliformis mosseae; in addition, the mycorrhizal symbiosis enhanced the fixing ability of N and the synthesis of amine. ④ The catabolism of fructose was inhibited under normal water condition, in addition to the catabolism of fructose was suppressed, the sorbitol catabolism was inhibited but the mannose synthesis was increased under the drought stress, they are the reasons why mycorrhizal P. mongolica maintaining a relatively high soluble sugar content before the drought stress; mycorrhizal formation inhibited main proline biosynthesis pathway, but increased the proline synthesis by secondary pathway, it is the reason why the proline contents of mycorrhizal and non-mycorrhizal P. mongolica changes little under different water treatments; in addition, mycorrhizal formation promoted the synthesis of red beet alkali under drought stress, these osmotic substances commonly maintaining the suitable osmotic pressure of mycorrhiza P. mongolica under the drought condition.⑤ Whether the well-waterd or the drought-stressed condition, mycorrhizal formation, the formation of mycorrhiza could inhibit the ROS production and fatty acid oxidation, the expression of antioxidant enzymes were significantly increased, and the expression of anti oxidase would be further enhanced under drought stress; Mycorrhizal P. mongolica enhanced the transition from GSH to GSSG, which could increase the NADPH supply for maintaining normal metabolism. ⑥ P. mongolica could activate the phytochrome, affect the circadian rhythm of plants under the drought stress when assoicated with the Funneliformis mosseae; Moreover, the genes expression of MAPK signal transduction pathway and calcium signal transduction pathway underdifferent water treatments were very beneficial for P. mongolica response to drought stress.(6) The cluster analysis results indicated that four samples can divide into two groups, non mycorrhizal Mongolian almond (DS and WW) and mycorrhizal Mongolian almond (MD and MW); The correlation analysis results indicated that the correlation of MD and DS is minimum, Mongolian almond and mycorrhizal Mongolian almond used 2 differently drought response mechanism.Our results provide a significant contribution to genetic engineering of Prunus plants, which may help to elucidate the theoretical basis of the mycorrhizal P. mongolica’s directive breeding. |
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