Miyamoto Y, Ishii Y, Honda A, Masunaka A, Tsuge T, Yamamoto M, Ohtani K, Fukumoto T, Gomi K, Peever T L, Akimitsu K
United Graduate School and Faculty of Agriculture, Kagawa University, Miki, Kagawa 761-0795 Japan.
Phytopathology. 2009 Apr;99(4):369-77. doi: 10.1094/PHYTO-99-4-0369.
The tangerine pathotype of Alternaria alternata produces host-selective ACT-toxin and causes Alternaria brown spot disease. Sequence analysis of a genomic cosmid clone identified a part of the ACTT gene cluster and implicated two genes, ACTT5 encoding an acyl-CoA synthetase and ACTT6 encoding an enoyl-CoA hydratase, in the biosynthesis of ACT-toxin. Genomic Southern blots demonstrated that both genes were present in tangerine pathotype isolates producing ACT-toxin and also in Japanese pear pathotype isolates producing AK-toxin and strawberry pathotype isolates producing AF-toxin. ACT-, AK-, and AF-toxins from these three pathotypes share a common 9,10-epoxy-8-hydroxy-9-methyl-decatrienoic acid moiety. Targeted gene disruption of two copies of ACTT5 significantly reduced ACT-toxin production and virulence. Targeted gene disruption of two copies of ACTT6 led to complete loss of ACT-toxin production and pathogenicity and a putative decatrienoic acid intermediate in ACT-toxin biosynthesis accumulated in mycelial mats. These results indicate that ACTT5 and ACTT6 are essential genes in ACT-toxin biosynthesis in the tangerine pathotype of A. alternata and both are required for full virulence of this fungus.
链格孢菌的柑橘致病型产生寄主选择性ACT毒素并引发链格孢褐斑病。对一个基因组黏粒克隆进行序列分析，鉴定出了ACTT基因簇的一部分，并表明两个基因，即编码酰基辅酶A合成酶的ACTT5和编码烯酰辅酶A水合酶的ACTT6参与了ACT毒素的生物合成。基因组Southern杂交显示，这两个基因既存在于产生ACT毒素的柑橘致病型分离株中，也存在于产生AK毒素的日本梨致病型分离株和产生AF毒素的草莓致病型分离株中。来自这三种致病型的ACT、AK和AF毒素都有一个共同的9,10-环氧-8-羟基-9-甲基-癸三烯酸部分。对两个拷贝的ACTT5进行靶向基因敲除显著降低了ACT毒素的产生和毒力。对两个拷贝的ACTT6进行靶向基因敲除导致ACT毒素的产生和致病性完全丧失，并且在菌丝垫中积累了ACT毒素生物合成中的一个假定的癸三烯酸中间体。这些结果表明，ACTT5和ACTT6是链格孢菌柑橘致病型ACT毒素生物合成中的必需基因，并且两者都是该真菌完全毒力所必需的。
