Bacterial Foodborne Pathogens and Mycology Research Unit, National Center for Agriculture Utilization Research, Peoria, IL 61604, USA.
Phytopathology. 2010 Jul;100(7):645-54. doi: 10.1094/PHYTO-100-7-0645.
Stenocarpella maydis causes both dry-ear rot and stalk rot of maize. Maize inbred lines have varying levels of resistance to ear rot caused by S. maydis. The genetic basis of resistance appears to rely on multiple genetic factors, none of which are known. The commonly used stiff-stalk inbred line B73 has been shown to be strongly susceptible to ear rot caused by S. maydis. Here, we report that the ChitA protein alloform from B73, ChitA-F, encoded by a known allele of the chiA gene, is susceptible to modification by a protein (Stm-cmp) secreted by S. maydis. We also identify a new allele of chiA (from inbred line LH82) which encodes ChitA-S, an alloform of ChitA that is resistant to Stm-cmp modification. Chitinase zymogram analysis of seed from a commercial field showed the presence of both ChitA alloforms in healthy ears, and showed that ChitA-F but not ChitA-S was modified in ears rotted by S. maydis. The ChitA-F protein was purified from inbred line B73 and ChitA-S from LH82. ChitA-F was modified more efficiently than ChitA-S by S. maydis protein extracts in vitro. The chiA gene from LH82 was cloned and sequenced. It is a novel allele that encodes six polymorphisms relative to the known allele from B73. This is the first demonstration that the susceptibility to modification of a fungal targeted plant chitinase differs among inbred lines. These findings suggest that the LH82 chiA allele may be a specific genetic determinant that contributes to resistance to ear rot caused by S. maydis whereas the B73 allele may contribute to susceptibility.
玉米弯孢菌可引起玉米干穗腐病和茎腐病。玉米自交系对玉米弯孢菌引起的穗腐病有不同程度的抗性。抗性的遗传基础似乎依赖于多个遗传因素，但目前尚不清楚。常用的硬秆自交系 B73 已被证明对玉米弯孢菌引起的穗腐病高度敏感。在这里，我们报告来自 B73 的 ChitA 蛋白同种型 ChitA-F，由 chiA 基因的一个已知等位基因编码，易受玉米弯孢菌分泌的蛋白（Stm-cmp）修饰。我们还鉴定了 chiA 的一个新等位基因（来自自交系 LH82），该等位基因编码 ChitA-S，是一种对 Stm-cmp 修饰具有抗性的 ChitA 同种型。来自商业田间的种子几丁质酶谱分析表明，健康穗中存在两种 ChitA 同种型，并且表明只有 ChitA-F 而不是 ChitA-S 在玉米弯孢菌引起的穗腐病中被修饰。从自交系 B73 中纯化了 ChitA-F 蛋白，从 LH82 中纯化了 ChitA-S 蛋白。在体外，ChitA-F 比 ChitA-S 更容易被玉米弯孢菌蛋白提取物修饰。从 LH82 克隆并测序了 chiA 基因。它是一个新的等位基因，与来自 B73 的已知等位基因相比，编码 6 个多态性。这是第一个证明真菌靶向植物几丁质酶的修饰易感性在自交系之间存在差异的证明。这些发现表明，LH82 chiA 等位基因可能是导致玉米弯孢菌引起的穗腐病抗性的特定遗传决定因素，而 B73 等位基因可能导致易感性。
