Graham Terrence L, Graham Madge Y, Subramanian Senthil, Yu Oliver
Department of Plant Pathology and Plant Molecular Biology and Biotechnology Program, Ohio State University, Columbus, Ohio 43210, USA.
Plant Physiol. 2007 Jun;144(2):728-40. doi: 10.1104/pp.107.097865. Epub 2007 Apr 6.
Isoflavonoids are thought to play an important role in soybean (Glycine max) resistance to Phytophthora sojae. This was addressed by silencing two genes for their biosynthesis and a third gene controlling their elicitation. Silencing of genes for isoflavone synthase (IFS) or chalcone reductase (CHR) was achieved in soybean roots through an Agrobacterium rhizogenes-mediated RNAi approach. Effectiveness of silencing was followed both by quantitative reverse transcriptase-polymerase chain reaction and high-performance liquid chromatography analyses. Silencing either IFS or CHR led to a breakdown of Rps-mediated resistance to race 1 of P. sojae in 'W79' (Rps 1c) or 'W82' (Rps 1k) soybean. Loss of resistance was accompanied by suppression of hypersensitive (HR) cell death in both cultivars and suppression of cell death-associated activation of hydrogen peroxide and peroxidase. The various results suggest that the 5-deoxyisoflavonoids play a critical role in the establishment of cell death and race-specific resistance. The P. sojae cell wall glucan elicitor, a potent elicitor of 5-deoxyisoflavonoids, triggered a cell death response in roots that was also suppressed by silencing either CHR or IFS. Furthermore, silencing of the elicitor-releasing endoglucanase (PR-2) led to a loss of HR cell death and race-specific resistance to P. sojae and also to a loss of isoflavone and cell death responses to cell wall glucan elicitor. Taken together, these results suggest that in situ release of active fragments from a general resistance elicitor (pathogen-associated molecular pattern) is necessary for HR cell death in soybean roots carrying resistance genes at the Rps 1 locus, and that this cell death response is mediated through accumulations of the 5-deoxyisoflavones.
异黄酮类化合物被认为在大豆（Glycine max）对大豆疫霉（Phytophthora sojae）的抗性中发挥重要作用。通过沉默两个参与其生物合成的基因和另一个控制其诱导的基因来研究这一问题。通过发根农杆菌介导的RNA干扰方法在大豆根中实现了异黄酮合酶（IFS）或查尔酮还原酶（CHR）基因的沉默。通过定量逆转录聚合酶链反应和高效液相色谱分析跟踪沉默的有效性。沉默IFS或CHR均导致‘W79’（Rps 1c）或‘W82’（Rps 1k）大豆中Rps介导的对大豆疫霉1号小种的抗性丧失。抗性丧失伴随着两个品种中超敏（HR）细胞死亡的抑制以及与细胞死亡相关的过氧化氢和过氧化物酶激活的抑制。各种结果表明，5-脱氧异黄酮类化合物在细胞死亡和小种特异性抗性的建立中起关键作用。大豆疫霉细胞壁葡聚糖激发子是5-脱氧异黄酮类化合物的有效激发子，可在根中引发细胞死亡反应，该反应也可通过沉默CHR或IFS来抑制。此外，激发子释放内切葡聚糖酶（PR-2）的沉默导致HR细胞死亡丧失、对大豆疫霉的小种特异性抗性丧失，还导致对细胞壁葡聚糖激发子的异黄酮和细胞死亡反应丧失。综上所述，这些结果表明，从一般抗性激发子（病原体相关分子模式）原位释放活性片段对于携带Rps 1位点抗性基因 的大豆根中的HR细胞死亡是必要的，并且这种细胞死亡反应是通过5-脱氧异黄酮的积累介导的。
