Chakrabarti Apratim, Panter Stephen N, Harrison Kate, Jones Jonathan D G, Jones David A
Research School of Biology, The Australian National University, Canberra ACT 0200, Australia.
Mol Plant Microbe Interact. 2009 Oct;22(10):1214-26. doi: 10.1094/MPMI-22-10-1214.
The tomato Cf-9 and Cf-9B genes both confer resistance to the leaf mold fungus Cladosporium fulvum but only Cf-9 confers seedling resistance and recognizes the avirulence (Avr) protein Avr9 produced by C. fulvum. Using domain swaps, leucine-rich repeats (LRR) 5 to 15 of Cf-9 were shown to be required for Cf-9-specific resistance to C. fulvum in tomato, and the entire N-terminus up to LRR15 of Cf-9B was shown to be required for Cf-9B-specific resistance. Finer domain swaps showed that nine amino-acid differences in LRR 13 to 15 provided sufficient Cf-9-specific residues in a Cf-9B context for recognition of Avr9 in Nicotiana tabacum or sufficient Cf-9B residues in a Cf-9 context for a novel necrotic response caused by the expression of Cf-9B in N. benthamiana. The responses conferred by LRR 13 to 15 were enhanced by addition of LRR 10 to 12, and either region of Cf-9B was found to cause necrosis in N. benthamiana when the other was replaced by Cf-9 sequence in a Cf-9B context. As a consequence, the domain swap with LRR 13 to 15 of Cf-9 in a Cf-9B context gained the dual ability to recognize Avr9 and cause necrosis in N. benthamiana. Intriguingly, two Cf-9B-specific domain swaps gave differing results for necrosis assays in N. benthamiana compared with disease resistance assays in transgenic tomato. The different domain requirements in these two cases suggest that the two assays detect unrelated ligands or detect related ligands in slightly different ways. A heat-sensitive necrosis-inducing factor present in N. benthamiana intercellular washing fluids was found to cause a necrotic response in N. tabacum plants carrying Hcr9-9A, Cf-9B, and Cf-9 but not in plants carrying only Cf-9. We postulate that this necrosis-inducing factor is recognized by Cf-9B either directly as a ligand or indirectly as a regulator of Cf-9B autoactivity.
番茄Cf - 9和Cf - 9B基因均赋予对叶霉病菌（Cladosporium fulvum）的抗性，但只有Cf - 9赋予幼苗抗性并识别叶霉病菌产生的无毒（Avr）蛋白Avr9。通过结构域交换实验表明，Cf - 9的富含亮氨酸重复序列（LRR）5至15对于番茄中Cf - 9对叶霉病菌的特异性抗性是必需的，而Cf - 9B直至LRR15的整个N端对于Cf - 9B的特异性抗性是必需的。更精细的结构域交换表明，LRR 13至15中的九个氨基酸差异在Cf - 9B背景下提供了足够的Cf - 9特异性残基，用于在烟草中识别Avr9，或者在Cf - 9背景下提供了足够的Cf - 9B残基，用于由Cf - 9B在本氏烟草中的表达引起的新的坏死反应。LRR 13至15赋予的反应通过添加LRR 10至12而增强，并且当Cf - 9B的一个区域在Cf - 9B背景下被Cf - 9序列取代时，发现Cf - 9B的任何一个区域都会在本氏烟草中引起坏死。因此，在Cf - 9B背景下与Cf - 9的LRR 13至15进行结构域交换获得了识别Avr9和在本氏烟草中引起坏死的双重能力。有趣的是，与转基因番茄中的抗病性测定相比，两个Cf - 9B特异性结构域交换在本氏烟草中的坏死测定给出了不同的结果。这两种情况下不同的结构域要求表明，这两种测定检测的是不相关的配体，或者是以略有不同的方式检测相关配体。在本氏烟草细胞间洗涤液中发现的一种热敏感坏死诱导因子，在携带Hcr9 - 9A、Cf - 9B和Cf - 9的烟草植株中会引起坏死反应，但在仅携带Cf - 9的植株中则不会。我们推测，这种坏死诱导因子要么被Cf - 9B直接识别为配体，要么被间接识别为Cf - 9B自身活性的调节剂。
