Role of the Host-Selective ACT-Toxin Synthesis Gene ACTTS2 Encoding an Enoyl-Reductase in Pathogenicity of the Tangerine Pathotype of Alternaria alternata

The tangerine pathotype of Alternaria alternata produces host-selective ACT-toxin and causes Alternaria brown spot disease of tangerines; and tangerine hybrids Sequence analysis of a genomic BAC clone identified a previously uncharacterized portion of the ACT-toxin biosynthesis gene cluster (ACTI) A L034-bp gene encoding a putative enoyl-reductase Was identified by using rapid amplification of CDNA ends and polymerase chain reaction and designated ACTTS2 Genomic Southern blots demonstrated that ACTTS2 is present only in ACT-toxin producers and is carried on a 1 9 Mb conditionally dispensable chromosome by the tangerine pathotype Targeted gene disruption of ACTTS2 led to a reduction in ACT-toxin production and pathogenicity, and transcriptional knockdown of ACTTS2 using RNA silencing resulted in complete loss of ACT-toxin production and pathogenicity. These results indicate that ACTTS2 is in essential gene for ACT-toxin biosynthesis in the tangerine pathotype of A alternata and is required for pathogenicity of this fungus