Polyploid plants often exhibit enhanced stress tolerance. The underlying physiological and molecular bases of such mechanisms remain elusive. Here, we characterized the drought tolerance of autotetraploid sour jujube at phenotypic, physiological and molecular levels. The study findings showed that the autotetraploid sour jujube exhibited a superior drought tolerance and enhanced regrowth potential after dehydration in comparison with the diploid counterpart. Under drought stress, more differentially expressed genes (DEGs) were detected in autotetraploid sour jujube and the physiological responses gradually triggered important functions. Through GO enrichment analysis, many DEGs between the diploid and autotetraploid sour jujube after drought-stress exposure were annotated to the oxidation–reduction process, photosystem, DNA binding transcription factor activity and oxidoreductase activity. Six reactive oxygen species scavenging-related genes were specifically differentially expressed and the larger positive fold-changes of the DEGs involved in glutathione metabolism were detected in autotetraploid. Consistently, the lower O2− level and malonaldehyde (MDA) content and higher antioxidant enzymes activity were detected in the autotetraploid under drought-stress conditions. In addition, DEGs in the autotetraploid after stress exposure were significantly enriched in anthocyanin biosynthesis, DNA replication, photosynthesis and plant hormone, including auxin, abscisic acid and gibberellin signal-transduction pathways. Under osmotic stress conditions, genes associated with the synthesis and transport of osmotic regulators including anthocyanin biosynthesis genes were differentially expressed, and the soluble sugar, soluble protein and proline contents were significantly higher in the autotetraploid. The higher chlorophyll content and DEGs enriched in photosynthesis suggest that the photosynthetic system in the autotetraploid was enhanced compared with diploid during drought stress. Moreover, several genes encoding transcription factors (TFs) including GRAS, Bhlh, MYB, WRKY and NAC were induced specifically or to higher levels in the autotetraploid under drought-stress conditions, and hub genes, LOC107403632, LOC107422279, LOC107434947, LOC107412673 and LOC107432609, related to 18 up-regulated transcription factors in the autotetraploid compared with the diploid were identified. Taken together, multiple responses contribute to the enhanced drought tolerance of autotetraploid sour jujube. This study could provide an important basis for elucidating the mechanism of tolerance variation after the polyploidization of trees.

中文翻译：

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多重响应有助于增强同源四倍体 Ziziphus jujuba Mill 的耐旱性。变种 刺

多倍体植物通常表现出增强的胁迫耐受性。这种机制的潜在生理和分子基础仍然难以捉摸。在这里，我们在表型、生理和分子水平上表征了同源四倍体酸枣的耐旱性。研究结果表明，与二倍体酸枣相比，四倍体酸枣表现出优异的耐旱性和脱水后的再生潜力。在干旱胁迫下，同源四倍体酸枣中检测到更多差异表达基因（DEGs），生理反应逐渐触发重要功能。通过 GO 富集分析，干旱胁迫暴露后二倍体和四倍体酸枣之间的许多 DEG 被注释为氧化还原过程、光系统、DNA结合转录因子活性和氧化还原酶活性。六个活性氧清除相关基因特异性差异表达，并且在同源四倍体中检测到参与谷胱甘肽代谢的 DEG 的较大正倍数变化。一致地，在干旱胁迫条件下，在同源四倍体中检测到较低的 O2− 水平和丙二醛 (MDA) 含量以及较高的抗氧化酶活性。此外，应激暴露后四倍体中的DEGs在花青素生物合成、DNA复制、光合作用和植物激素方面显着富集，包括生长素、脱落酸和赤霉素信号转导途径。在渗透胁迫条件下，包括花青素生物合成基因在内的与渗透调节剂合成和转运相关的基因差异表达，其可溶性糖、可溶性蛋白和脯氨酸含量在同源四倍体中显着升高。较高的叶绿素含量和光合作用中富含的 DEG 表明，在干旱胁迫期间，与二倍体相比，同源四倍体的光合系统得到增强。此外，在干旱胁迫条件下，同源四倍体中的几个编码转录因子 (TF) 的基因包括 GRAS、Bhlh、MYB、WRKY 和 NAC 被特异性诱导或达到更高水平，以及枢纽基因 LOC107403632、LOC107422279、LOC107434947、LOC107430C1206与二倍体相比，同源四倍体中的 18 个上调转录因子相关。综合起来，多重响应有助于增强同源四倍体酸枣的耐旱性。该研究可为阐明树木多倍化后耐受性变异的机制提供重要依据。