RAR1 positively controls steady state levels of barley MLA resistance proteins and enables sufficient MLA6 accumulation for effective resistance
RAR1 positively controls steady state levels of barley MLA resistance proteins and enables sufficient MLA6 accumulation for effective resistance
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DOI：
10.1105/tpc.104.026682
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发表时间：
2004-12-01
期刊：
影响因子：
11.6
通讯作者：
Schulze-Lefert, P
中科院分区：
文献类型：
--
作者：
Bieri, S;Mauch, S;Schulze-Lefert, P
多态性大麦（Hordeum vulgare）Mla基因座具有对白粉病真菌大麦白粉病菌大麦亚种（Blumeria graminis f sp hordei）的等位小种特异性抗性（R）基因。高度序列相关的MLA蛋白含有N-末端卷曲螺旋结构、中心核苷酸结合（NB）位点、富含亮氨酸重复序列（LRR）区和C-末端非LRR区。使用转基因大麦株系表达表位标记的MLA 1和MLA 6衍生物驱动的天然调控序列，我们显示了可逆的和盐浓度依赖性分布的细胞内MLA蛋白在可溶性和膜相关的池。转录后过程指导MLA 1超过MLA 6四倍的积累。出乎意料的是，在MLA 6抗性受损而不是MLA 1抗性受损的rar 1突变体植物中，两种MLA同种型的稳态水平降低。此外，MLA 1/MLA 6杂合蛋白的差异稳态水平与它们对RAR 1的需求相关; RAR 1独立杂合蛋白积累到较高水平，RAR 1依赖杂合蛋白积累到较低水平。有趣的是，酵母双杂交研究表明，RAR 1独立但不依赖RAR 1的MLA亚型的LRR结构域与SGT 1相互作用，SGT 1是许多NB-LRR型R蛋白功能所需的RAR 1相互作用蛋白。我们的研究结果暗示存在一种保守的机制，以达到触发有效抗性反应所需的最低NB-LRR R蛋白阈值。
The polymorphic barley (Hordeum vulgare) Mla locus harbors allelic race-specific resistance (R) genes to the powdery mildew fungus Blumeria graminis f sp hordei. The highly sequence-related MLA proteins contain an N-terminal coiled-coil structure, a central nucleotide binding (NB) site, a Leu-rich repeat (LRR) region, and a C-terminal non-LRR region. Using transgenic barley lines expressing epitope-tagged MLA1 and MLA6 derivatives driven by native regulatory sequences, we show a reversible and salt concentration-dependent distribution of the intracellular MLA proteins in soluble and membrane-associated pools. A posttranscriptional process directs fourfold greater accumulation of MLA1 over MLA6. Unexpectedly, in rar1 mutant plants that are compromised for MLA6 but not MLA1 resistance, the steady state level of both MLA isoforms is reduced. Furthermore, differential steady state levels of MLA1/MLA6 hybrid proteins correlate with their requirement for RAR1; the RAR1-independent hybrid protein accumulates to higher levels and the RAR1-dependent one to lower levels. Interestingly, yeast two-hybrid studies reveal that the LRR domains of RAR1-independent but not RAR1-dependent MLA isoforms interact with SGT1, a RAR1 interacting protein required for the function of many NB-LRR type R proteins. Our findings implicate the existence of a conserved mechanism to reach minimal NB-LRR R protein thresholds that are needed to trigger effective resistance responses.