Phytopathology. 1999 Oct;89(10):908-14. doi: 10.1094/PHYTO.1999.89.10.908.
ABSTRACT Aspergillus flavus is the causal agent of an ear and kernel rot in maize. In this study, we characterized an alpha-amylase-deficient mutant and assessed its ability to infect and produce aflatoxin in wounded maize kernels. The alpha-amylase gene Amy1 was isolated from A. flavus, and its DNA sequence was determined to be nearly identical to Amy3 of A. oryzae. When Amy1 was disrupted in an aflatoxigenic strain of A. flavus, the mutant failed to produce extracellular alpha-amylase and grew 45% the rate of the wild-type strain on starch medium. The mutant produced aflatoxin in medium containing glucose but not in a medium containing starch. The alpha-amylase-deficient mutant produced aflatoxin in maize kernels with wounded embryos and occasionally produced aflatoxin only in embryos of kernels with wounded endosperm. The mutant strain failed to produce aflatoxin when inoculated onto degermed kernels. In contrast, the wild-type strain produced aflatoxin in both the endosperm and embryo. These results suggest that alpha-amylase facilitates aflatoxin production and growth of A. flavus from a wound in the endosperm to the embryo. A 14-kDa trypsin inhibitor associated with resistance to A. flavus and aflatoxin in maize also inhibited the alpha-amylase from A. flavus, indicating that it is a bifunctional inhibitor. The inhibitor may have a role in resistance, limiting the growth of the fungus in the endosperm tissue by inhibiting the degradation of starch.
摘要黄曲霉是引起玉米穗部和籽粒腐烂的病原菌。本研究对一株α-淀粉酶缺陷突变株进行了鉴定，并评估了其侵染和产生黄曲霉毒素的能力。我们从黄曲霉中克隆到α-淀粉酶基因 Amy1，其 DNA 序列与米曲霉 Amy3 高度同源。当在产毒黄曲霉野生型菌株中敲除 Amy1 后，突变株丧失了产生胞外α-淀粉酶的能力，在淀粉培养基上的生长速度仅为野生型的 45%。该突变株在含有葡萄糖的培养基中可以产生黄曲霉毒素，但在含有淀粉的培养基中不能产生。α-淀粉酶缺陷突变株在带有损伤胚的玉米籽粒中产生黄曲霉毒素，但偶尔在损伤胚乳的玉米籽粒中仅产生黄曲霉毒素。当接种在去胚的玉米籽粒上时，突变株无法产生黄曲霉毒素。相比之下，野生型菌株在胚乳和胚中均能产生黄曲霉毒素。这些结果表明，α-淀粉酶促进了黄曲霉从胚乳的伤口向胚的生长，从而有利于黄曲霉毒素的产生。与玉米对黄曲霉和黄曲霉毒素的抗性相关的一种 14kDa 的胰蛋白酶抑制剂也能抑制黄曲霉的α-淀粉酶，这表明它是一种双功能抑制剂。该抑制剂可能在抗性中发挥作用，通过抑制淀粉的降解，限制真菌在胚乳组织中的生长。
