Ito Kaoru, Tanaka Takayoshi, Hatta Rieko, Yamamoto Mikihiro, Akimitsu Kazuya, Tsuge Takashi
Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya 464-8601, Japan.
Mol Microbiol. 2004 Apr;52(2):399-411. doi: 10.1111/j.1365-2958.2004.04004.x.
The filamentous fungus Alternaria alternata contains seven pathogenic variants (pathotypes), which produce different host-specific toxins and cause diseases on different plants. The strawberry pathotype produces host-specific AF-toxin and causes Alternaria black spot of strawberry. This pathotype is also pathogenic to Japanese pear cultivars susceptible to the Japanese pear pathotype that produces AK-toxin. The strawberry pathotype produces two related molecular species, AF-toxins I and II: toxin I is toxic to both strawberry and pear, and toxin II is toxic only to pear. Previously, we isolated a cosmid clone pcAFT-1 from the strawberry pathotype that contains three genes involved in AF-toxin biosynthesis. Here, we have identified a new gene, designated AFTS1, from pcAFT-1. AFTS1 encodes a protein with similarity to enzymes of the aldo-ketoreductase superfamily. Targeted mutation of AFTS1 diminished the host range of the strawberry pathotype: Delta aftS1 mutants were pathogenic to pear, but not to strawberry, as is the Japanese pear pathotype. These mutants were found to produce AF-toxin II, but not AF-toxin I. These data represent a novel example of how the host range of a plant pathogenic fungus can be restricted by modification of secondary metabolism.
丝状真菌链格孢菌包含七个致病变种（致病型），它们产生不同的寄主特异性毒素，并在不同植物上引发病害。草莓致病型产生寄主特异性AF毒素，并导致草莓链格孢黑斑病。该致病型对易受产生AK毒素的日本梨致病型影响的日本梨品种也具有致病性。草莓致病型产生两种相关的分子种类，即AF毒素I和II：毒素I对草莓和梨都有毒，而毒素II仅对梨有毒。此前，我们从草莓致病型中分离出一个黏粒克隆pcAFT - 1，它包含三个参与AF毒素生物合成的基因。在此，我们从pcAFT - 1中鉴定出一个新基因，命名为AFTS1。AFTS1编码一种与醛酮还原酶超家族的酶具有相似性的蛋白质。对AFTS1进行靶向突变缩小了草莓致病型的寄主范围：ΔaftS1突变体对梨具有致病性，但对草莓不具有致病性，就像日本梨致病型一样。这些突变体被发现能产生AF毒素II，但不能产生AF毒素I。这些数据代表了一个新的例子，说明植物病原真菌的寄主范围如何通过次生代谢的修饰而受到限制。
