Kuluev Bulat, Avalbaev Azamat, Mikhaylova Elena, Nikonorov Yuriy, Berezhneva Zoya, Chemeris Alexey
Institute of Biochemistry and Genetics, Ufa Research Centre, Russian Academy of Sciences, pr. Oktyabrya 71, Ufa 450054, Russia.
Institute of Biochemistry and Genetics, Ufa Research Centre, Russian Academy of Sciences, pr. Oktyabrya 71, Ufa 450054, Russia.
J Plant Physiol. 2016 Nov 1;206:1-12. doi: 10.1016/j.jplph.2016.09.001. Epub 2016 Sep 9.
Changes in the expression levels of tobacco expansin genes NtEXPA1, NtEXPA4, NtEXPA5, and NtEXPA6 were studied in different organs of tobacco (Nicotiana tabacum L.) as well as in response to phytohormone and stress treatments. It was shown that NtEXPA1, NtEXPA4 and NtEXPA5 transcripts were predominantly expressed in the shoot apices and young leaves, but almost absent in mature leaves and roots. The NtEXPA6 mRNA was found at high levels in calluses containing a large number of undifferentiated cells, but hardly detectable in the leaves of different ages and roots. In young leaves, expression levels of NtEXPA1, NtEXPA4 and NtEXPA5 genes were induced by cytokinins, auxins and gibberellins. Cytokinins and auxins were also found to increase NtEXPA6 transcripts in young leaves but to the much lower levels than the other expansin mRNAs. Expression analysis demonstrated that brassinosteroid phytohormones were able either to up-regulate or to down-regulate expression of different expansins in leaves of different ages. Furthermore, transcript levels of NtEXPA1, NtEXPA4, and NtEXPA5 genes were increased in response to NaCl, drought, cold, heat, and 10μM abscisic acid (ABA) treatments but reduced in response to more severe stresses, i.e. cadmium, freezing, and 100μM ABA. In contrast, no substantial changes were found in NtEXPA6 transcript level after all stress treatments. In addition, we examined the involvement of tobacco expansins in the regulation of abiotic stress tolerance by transgenic approaches. Transgenic tobacco plants with constitutive expression of NtEXPA1 and NtEXPA5 exhibited improved tolerance to salt stress: these plants showed higher growth indices after NaCl treatment and minimized water loss by reducing stomatal density. In contrast, NtEXPA4-silenced plants were characterized by a considerable growth reduction under salinity and enhanced water loss. Our findings indicate that expression levels of all studied tobacco expansins genes are modulated by plant hormones whereas NtEXPA1, NtEXPA4, and NtEXPA5 expansins may be involved in the regulation of stress tolerance in tobacco plants.
研究了烟草（Nicotiana tabacum L.）不同器官中烟草扩张蛋白基因NtEXPA1、NtEXPA4、NtEXPA5和NtEXPA6的表达水平变化，以及它们对植物激素和胁迫处理的响应。结果表明，NtEXPA1、NtEXPA4和NtEXPA5转录本主要在茎尖和幼叶中表达，但在成熟叶和根中几乎不表达。在含有大量未分化细胞的愈伤组织中发现NtEXPA6 mRNA水平较高，但在不同年龄的叶片和根中几乎检测不到。在幼叶中，细胞分裂素、生长素和赤霉素可诱导NtEXPA1、NtEXPA4和NtEXPA5基因的表达水平。还发现细胞分裂素和生长素可增加幼叶中NtEXPA6转录本，但增加幅度远低于其他扩张蛋白mRNA。表达分析表明，油菜素甾体类植物激素能够上调或下调不同年龄叶片中不同扩张蛋白的表达。此外，NtEXPA1、NtEXPA4和NtEXPA5基因的转录水平在NaCl、干旱、低温、高温和10μM脱落酸（ABA）处理后升高，但在更严重的胁迫（即镉、冷冻和100μM ABA）处理后降低。相比之下，所有胁迫处理后NtEXPA6转录水平均未发现显著变化。此外，我们通过转基因方法研究了烟草扩张蛋白在非生物胁迫耐受性调控中的作用。组成型表达NtEXPA1和NtEXPA5的转基因烟草植株对盐胁迫的耐受性增强：这些植株在NaCl处理后表现出更高的生长指标，并通过降低气孔密度使水分损失最小化。相比之下，NtEXPA4基因沉默的植株在盐胁迫下生长显著降低，水分损失增加。我们的研究结果表明，所有研究的烟草扩张蛋白基因的表达水平受植物激素调控，而NtEXPA1、NtEXPA4和NtEXPA5扩张蛋白可能参与烟草植株胁迫耐受性的调控。
