USDA, ARS, Appalachian Fruit Research Station, 2217 Wiltshire Road, Kearneysville, WV 25430, USA.
BMC Plant Biol. 2014 Jul 8;14:182. doi: 10.1186/1471-2229-14-182.
Individual plants adapt to their immediate environment using a combination of biochemical, morphological and life cycle strategies. Because woody plants are long-lived perennials, they cannot rely on annual life cycle strategies alone to survive abiotic stresses. In this study we used suppression subtractive hybridization to identify genes both up- and down-regulated in roots during water deficit treatment and recovery. In addition we followed the expression of select genes in the roots, leaves, bark and xylem of 'Royal Gala' apple subjected to a simulated drought and subsequent recovery.
In agreement with studies from both herbaceous and woody plants, a number of common drought-responsive genes were identified, as well as a few not previously reported. Three genes were selected for more in depth analysis: a high affinity nitrate transporter (MdNRT2.4), a mitochondrial outer membrane translocase (MdTOM7.1), and a gene encoding an NPR1 homolog (MpNPR1-2). Quantitative expression of these genes in apple roots, bark and leaves was consistent with their roles in nutrition and defense.
Additional genes from apple roots responding to drought were identified using suppression subtraction hybridization compared to a previous EST analysis from the same organ. Genes up- and down-regulated during drought recovery in roots were also identified. Elevated levels of a high affinity nitrate transporter were found in roots suggesting that nitrogen uptake shifted from low affinity transport due to the predicted reduction in nitrate concentration in drought-treated roots. Suppression of a NPR1 gene in leaves of drought-treated apple trees may explain in part the increased disease susceptibility of trees subjected to dehydrative conditions.
个体植物通过生化、形态和生命周期策略的组合来适应其直接环境。由于木本植物是长寿的多年生植物，它们不能仅依靠年度生命周期策略来应对非生物胁迫。在这项研究中，我们使用抑制差减杂交来鉴定在水分亏缺处理和恢复过程中根中上调和下调的基因。此外，我们还跟踪了 '皇家 Gala' 苹果根、叶、树皮和木质部中选定基因的表达，这些苹果受到模拟干旱和随后恢复的影响。
与草本和木本植物的研究一致，鉴定出了一些常见的耐旱响应基因，以及一些以前未报道过的基因。选择了三个基因进行更深入的分析：一个高亲和力硝酸盐转运蛋白（MdNRT2.4）、一个线粒体外膜转运蛋白（MdTOM7.1）和一个编码 NPR1 同源物的基因（MpNPR1-2）。这些基因在苹果根、树皮和叶中的定量表达与其在营养和防御中的作用一致。
与同一器官之前的 EST 分析相比，使用抑制差减杂交从苹果根中鉴定出了更多对干旱有反应的基因。还鉴定了根中干旱恢复过程中上调和下调的基因。在根中发现高亲和力硝酸盐转运蛋白水平升高，表明由于预测干旱处理根中硝酸盐浓度降低，氮吸收从低亲和力转运转移。干旱处理苹果树叶片中 NPR1 基因的抑制可能部分解释了树木在脱水条件下易患病的原因。
