Short-term transcriptomic responses of Populus euphratica roots and leaves to drought stress

Populus euphratica Oliv.,the Euphrates poplar,is the tallest tree species in the arid desert areas of Northwest China.Investigation of its drought-resistance genes is valuable to increase understanding of drought resistance mechanisms.RNA-seq of leaves and roots under drought simulation by 25%polyethylene glycol-6000(PEG 6000)were performed at 0,4,and 12 h.Leaves and roots responded differently to drought via differentially upregulated and downregulated genes;more genes were downregulated than upregulated in both leaves and roots.Additionally,these differentially expressed genes were enriched in different GO terms and KEGG pathways.For example,GO term‘response to organic substance’and KEGG pathway‘nitrogen metabolism’were enriched for drought-stressed leaves,while GO term‘cell wall organization or biogenesis’and KEGG pathway‘zeatin biosynthesis’were enriched for drought-stressed roots.The enrichment of the GO term‘enzyme linked receptor protein signalling pathway’in both leaf and root drought responses suggests that these tissues may also have similar mechanisms.However,roots under drought stress for four hs responded by activating programed cell death.The KEGG pathway‘plant hormone signal transduction’was detected for 4-and 12-h droughtstressed leaves and 12-h drought-stressed roots,suggesting that plant hormone signal transduction plays an important role in both roots and leaves.GO enrichment of upregulated and downregulated genes for leaves and roots reflect differentially regulatory mechanisms of response to drought stress via different biological processes such as the regulation of photosynthesis and auxin signalling pathway in leaves,and the regulation of defence response and water homeostasis in roots.Fifteen candidate genes,including transcription factors,protein kinase,transporter,late embryogenesis abundant protein and mannitol dehydrogenase,were further selected to determine their response to drought using qRTPCR.The results show that the expression patterns of 13 of the 15 genes correspond to the RNA-seq results.This study provides new insights into the drought response mechanism of P.euphratica and suggests new candidate gene resources.

中国西北地区天然胡杨群体遗传多样性及核心保护单元的构建

胡杨(Populus euphratica)是极端干旱荒漠区的珍稀乔木树种。为了确定天然胡杨群体遗传多样性保护单元并挖掘优异的种质资源,本研究以中国西北地区新疆、青海、甘肃、宁夏、内蒙古的58个天然胡杨群体为研究对象,利用120个位点的SNPs标记对这些胡杨群体进行群体遗传结构和遗传多样性分析,并根据不同群体间Nei’s遗传相似度,采用逐步聚类优先取样法对初始群体、遗传多样性保护单元和剩余群体进行t检验。群体结构和主成分分析表明,胡杨群体可分为新疆南疆(SX)、新疆北疆(NX)、青海(QH)和混合群(甘肃、宁夏和内蒙古混合群,GNM)4个分支,遗传多样性分析表明新疆南疆(SX)遗传多样性高于其他群体。分子方差分析(AMOVA)表明天然胡杨群体的遗传变异主要分布在各个群体内。构建了天然胡杨群体一级核心保护单元3个群体(CU3),二级核心保护单元33个群体(CU33)。南疆存在较多优异抗逆的天然胡杨古树资源,南疆分布区的平均遗传多样性水平最高。综上所述,南疆地区胡杨古树遗传多样性整体高于北疆及疆外地区,结合新疆地区干旱严重指数等生境信息,建议加大对南疆胡杨古树群体的保护力度,重视北疆胡杨林的更新换代。