‘美人’梅在干旱胁迫下的生理响应及相关基因筛选

Physiological responses and transcriptional regulation of Prunus mume ‘Meiren’ under drought stress

摘要:

梅花(Prunus mume)是药食同源的生态经济型树种，然而，干旱严重限制了梅花在我国北方干旱、半干旱地区的推广栽培。本研究以‘美人’梅为试验材料，采用自然干旱法进行处理，测定渗透调节物质、光合参数和抗氧化酶活性等光合生理指标，并使用转录组测序探究梅花在干旱胁迫下的内在调控机制。结果表明，随着干旱胁迫程度加深，‘美人’梅的叶绿素a (chlorophyll a,Chla)、叶绿素b (chlorophyll b,Chlb)、叶绿素(a+b)[chlorophyll (a+b),Chl (a+b)]含量以及可溶性蛋白(soluble protein,SP)含量呈现先上升后下降的趋势，净光合速率(photosynthetic rate,Pn)、气孔导度(stomatal conductance,Gs)和蒸腾速率(transpiration rate,Tr)以及最大光化学效率(maximum photochemical efficiency,Fv/Fm)、实际光化学电子产量[effective photochemical quantum yield,Y (II)]、光化学猝灭系数(photochemical quenching,qP)、相对电子传递效率(electron transport rate,ETR)均显著下降，而丙二醛含量(malondialdehyde,MDA)、抗氧化酶如超氧化物歧化酶(superoxide dismutase,SOD)活性、过氧化物酶(peroxidase,POD)和渗透调节物质的积累显著增强。转录组测序共获得24 853个高质量基因。GO富集显示重度干旱下差异表达基因(differentially expressed genes,DEGs)富集程度最高。KEGG (Kyoto encylopaedia of genes and genomes,KEGG)分析显示次级代谢物的生物合成(biosynthesis of secondary metabolites)、植物与病原体相互作用(plant-pathogen interaction)、植物激素信号传导(plant hormone signal transduction)、淀粉和蔗糖代谢(starch and sucrose metabolism)、丝裂原活化蛋白激酶(mitogen-activated protein kinase,MAPK)信号通路是4个干旱时期中最显著富集的代谢通路。此外，还筛选到16个与‘美人’梅抗旱相关的关键基因。本研究发现梅花可能通过MYB、ERF、bHLH、NAC和WRKY等转录因子(transcription factors,TF)调节抗旱相关基因SUS、P5CS、LEA、SOD、POD、SOD1、TPPD、TPPA等的表达，促进蔗糖等渗透调节物质积累，提高SOD、POD等抗氧化酶活性，减弱逆境胁迫下活性氧的危害，保护膜系统的结构和功能以抵御干旱。本研究结果为进一步挖掘梅花响应干旱胁迫的候选基因和抗旱育种提供了理论参考。

关键词:梅花;干旱胁迫;生理特性;转录组

Abstract:

Prunus mume is an ecologically and economically valuable plant with both medicinal and edible values. However, drought severely limits the promotion and cultivation of P. mume in the arid and semi-arid areas in northern China. In this study, we treated P. mume ‘Meiren’ with natural drought and then assessed photosynthetic and physiological indexes such as osmoregulatory substances, photosynthetic parameters, and antioxidant enzyme activities. Furthermore, we employed transcriptome sequencing to explore the internal regulatory mechanism of P. mume under drought stress. As the drought stress aggravated, the levels of chlorophyll a (Chla), chlorophyll b (Chlb), chlorophyll (a+b)[Chl(a+b)], and soluble protein (SP) in P. mume first elevated and then declined. The net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), maximum photochemical efficiency (Fv/Fm), effective photochemical quantum yield [Y(II)], photochemical quenching (qP), and relative electron transport rate (ETR) all kept decreasing, while the levels of malondialdehyde, superoxide dismutase (SOD), peroxidase (POD), and osmoregulatory substances rose. Transcriptome sequencing revealed a total of 24 853 high-quality genes. Gene ontology (GO) enrichment showed that differentially expressed genes (DEGs) were the most under severe drought. Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis showed that the DEGs during the four drought periods were mainly involved in the biosynthesis of secondary metabolites, plant-pathogen interaction, plant hormone signal transduction, starch and sucrose metabolism, and mitogen-activated protein kinase signaling pathways. Furthermore, we identified 16 key genes associated with the drought tolerance of P. mume ‘Meiren’. This study discovered that P. mume might up-regulate or down-regulate the expression of drought tolerance-related genes such as SUS, P5CS, LEA, SOD, POD, SOD1, TPPD, and TPPA via transcription factors like MYB, ERF, bHLH, NAC, and WRKY to promote the accumulation of osmoregulatory substances like sucrose and enhance the activities of antioxidant enzymes such as SOD and POD, thus reducing the harm of reactive oxygen species and protecting the structure and function of the membrane system under drought stress. The findings provide theoretical references for further exploration of candidate genes of P. mume in response to drought stress and breeding of drought-tolerant varieties.

Key words:Prunus mume;drought stress;physiological characteristics;transcriptome