Department of Plant Pathology, The Pennsylvania State University, University Park, PA 16802, USA.
BMC Genomics. 2012 Jan 9;13:9. doi: 10.1186/1471-2164-13-9.
Desirable apple varieties are clonally propagated by grafting vegetative scions onto rootstocks. Rootstocks influence many phenotypic traits of the scion, including resistance to pathogens such as Erwinia amylovora, which causes fire blight, the most serious bacterial disease of apple. The purpose of the present study was to quantify rootstock-mediated differences in scion fire blight susceptibility and to identify transcripts in the scion whose expression levels correlated with this response.
Rootstock influence on scion fire blight resistance was quantified by inoculating three-year old, orchard-grown apple trees, consisting of 'Gala' scions grafted to a range of rootstocks, with E. amylovora. Disease severity was measured by the extent of shoot necrosis over time. 'Gala' scions grafted to G.30 or MM.111 rootstocks showed the lowest rates of necrosis, while 'Gala' on M.27 and B.9 showed the highest rates of necrosis. 'Gala' scions on M.7, S.4 or M.9F56 had intermediate necrosis rates. Using an apple DNA microarray representing 55,230 unique transcripts, gene expression patterns were compared in healthy, un-inoculated, greenhouse-grown 'Gala' scions on the same series of rootstocks. We identified 690 transcripts whose steady-state expression levels correlated with the degree of fire blight susceptibility of the scion/rootstock combinations. Transcripts known to be differentially expressed during E. amylovora infection were disproportionately represented among these transcripts. A second-generation apple microarray representing 26,000 transcripts was developed and was used to test these correlations in an orchard-grown population of trees segregating for fire blight resistance. Of the 690 transcripts originally identified using the first-generation array, 39 had expression levels that correlated with fire blight resistance in the breeding population.
Rootstocks had significant effects on the fire blight susceptibility of 'Gala' scions, and rootstock-regulated gene expression patterns could be correlated with differences in susceptibility. The results suggest a relationship between rootstock-regulated fire blight susceptibility and sorbitol dehydrogenase, phenylpropanoid metabolism, protein processing in the endoplasmic reticulum, and endocytosis, among others. This study illustrates the utility of our rootstock-regulated gene expression data sets for candidate trait-associated gene data mining.
理想的苹果品种是通过将营养枝接穗嫁接到砧木上来无性繁殖的。砧木会影响接穗的许多表型特征，包括对病原体的抗性，如引起火疫病的欧文氏菌，这是苹果最严重的细菌性疾病。本研究的目的是量化砧木对接穗火疫病易感性的影响，并鉴定与该反应相关的接穗中表达水平的转录本。
通过用欧文氏菌接种三年生、果园生长的苹果树上的“Gala”接穗，来量化砧木对接穗抗病性的影响。通过随时间推移的枝条坏死程度来衡量疾病严重程度。接穗嫁接到 G.30 或 MM.111 砧木上的“Gala”表现出最低的坏死率，而接穗嫁接到 M.27 和 B.9 砧木上的表现出最高的坏死率。接穗嫁接到 M.7、S.4 或 M.9F56 砧木上的坏死率居中。使用代表 55230 个独特转录本的苹果 DNA 微阵列，比较了同一系列砧木上温室中健康、未接种的“Gala”接穗的基因表达模式。我们鉴定了 690 个转录本，其稳态表达水平与接穗/砧木组合的火疫病易感性程度相关。这些转录本中不成比例地包含了在欧文氏菌感染过程中表达水平不同的转录本。开发了第二代苹果微阵列，代表 26000 个转录本，并在分离火疫病抗性的果园生长的树木群体中测试了这些相关性。在最初使用第一代微阵列鉴定的 690 个转录本中，有 39 个转录本的表达水平与繁殖群体中的火疫病抗性相关。
砧木对接穗的火疫病易感性有显著影响，并且砧木调控的基因表达模式可以与易感性差异相关。结果表明，砧木调控的火疫病易感性与山梨醇脱氢酶、苯丙烷代谢、内质网蛋白质加工和内吞作用等有关。本研究说明了我们的砧木调控基因表达数据集在候选性状相关基因数据挖掘中的应用。
