Mongolian Almond (<i>Prunus mongolica</i> Maxim): The Morpho-Physiological, Biochemical and Transcriptomic Response to Drought Stress

<div><p><i>Prunus mongolica</i> Maxim, which is widely established in the Gobi Desert, shows extreme tolerance to drought. However, there is a lack of available transcriptomic resources for this species related to its response to water deficiency. To investigate the mechanisms that allow <i>P</i>. <i>mongolica</i> to maintain growth in extremely arid environments, the response of <i>P</i>. <i>mongolica</i> seedlings to drought stress was analyzed using morphological, physiological, biochemical and high-throughput sequencing approaches. We generated 28,713,735 and 26,650,133 raw reads from no-stress control and drought-stressed <i>P</i>. <i>mongolica</i> 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. 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 <i>P</i>. <i>mongolica</i> survival in Gobi Desert. 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 <i>P</i>. <i>mongolica</i> seedlings. In addition, activation of iron superoxide dismutase transcription and enhanced transcription of manganese superoxide dismutase were observed in <i>P</i>. <i>mongolica</i> to promote tolerance of drought stress. This study identified drought response genes in <i>P</i>. <i>mongolica</i> seedlings. Our results provide a significant contribution to the understanding of how <i>P</i>. <i>mongolica</i> responds to drought stress at the transcriptome level, which may help to elucidate molecular mechanisms associated with the drought response of almond plants.</p>