Mulozi Lungowe, Vennapusa Amaranatha R, Elavarthi Sathya, Jacobs Oluwatomi E, Kulkarni Krishnanand P, Natarajan Purushothaman, Reddy Umesh K, Melmaiee Kalpalatha
Department of Agriculture and Natural Resources, Delaware State University, Dover, DE, United States.
Department of Biology and Gus R. Douglass Institute, West Virginia State University, Institute, WV, United States.
Front Plant Sci. 2023 Apr 19;14:1150204. doi: 10.3389/fpls.2023.1150204. eCollection 2023.
Sugar maple ( Marshall) is a temperate tree species in the northeastern parts of the United States and is economically important for its hardwood and syrup production. Sugar maple trees are highly vulnerable to changing climatic conditions, especially drought, so understanding the physiological, biochemical, and molecular responses is critical. The sugar maple saplings were subjected to drought stress for 7, 14, and 21 days and physiological data collected at 7, 14, and 21 days after stress (DAS) showed significantly reduced chlorophyll and Normalized Difference Vegetation Index with increasing drought stress time. The drought stress-induced biochemical changes revealed a higher accumulation of malondialdehyde, proline, and peroxidase activity in response to drought stress. Transcriptome analysis identified a total of 14,099 differentially expressed genes (DEGs); 328 were common among all stress periods. Among the DEGs, transcription factors (including NAC, HSF, ZFPs, GRFs, and ERF), chloroplast-related and stress-responsive genes such as peroxidases, membrane transporters, kinases, and protein detoxifiers were predominant. GO enrichment and KEGG pathway analysis revealed significantly enriched processes related to protein phosphorylation, transmembrane transport, nucleic acids, and metabolic, secondary metabolite biosynthesis pathways, circadian rhythm-plant, and carotenoid biosynthesis in response to drought stress. Time-series transcriptomic analysis revealed changes in gene regulation patterns in eight different clusters, and pathway analysis by individual clusters revealed a hub of stress-responsive pathways. In addition, qRT-PCR validation of selected DEGs revealed that the expression patterns were consistent with transcriptome analysis. The results from this study provide insights into the dynamics of physiological, biochemical, and gene responses to progressive drought stress and reveal the important stress-adaptive mechanisms of sugar maple saplings in response to drought stress.
糖枫（马歇尔）是美国东北部的一种温带树种，因其硬木和糖浆生产而具有重要的经济价值。糖枫极易受到气候变化的影响，尤其是干旱，因此了解其生理、生化和分子反应至关重要。对糖枫树苗进行了7天、14天和21天的干旱胁迫处理，在胁迫后7天、14天和21天收集的生理数据显示，随着干旱胁迫时间的增加，叶绿素和归一化植被指数显著降低。干旱胁迫诱导的生化变化表明，在干旱胁迫下，丙二醛、脯氨酸积累增加，过氧化物酶活性增强。转录组分析共鉴定出14099个差异表达基因（DEG）；其中328个在所有胁迫时期都有出现。在这些差异表达基因中，转录因子（包括NAC、HSF、锌指蛋白、GRF和ERF）、与叶绿体相关的基因以及应激反应基因如过氧化物酶、膜转运蛋白、激酶和蛋白质解毒剂占主导地位。基因本体（GO）富集分析和京都基因与基因组百科全书（KEGG）通路分析显示，与蛋白质磷酸化、跨膜运输、核酸、代谢、次生代谢物生物合成途径、昼夜节律-植物以及类胡萝卜素生物合成相关的过程在干旱胁迫下显著富集。时间序列转录组分析揭示了八个不同簇中基因调控模式的变化，对各个簇的通路分析揭示了一个应激反应通路枢纽。此外，对选定差异表达基因的qRT-PCR验证表明，其表达模式与转录组分析一致。本研究结果为深入了解糖枫树苗对渐进性干旱胁迫的生理、生化和基因反应动态提供了见解，并揭示了糖枫树苗应对干旱胁迫的重要应激适应机制。
