Role of the pathotype-specific ACRTS1 gene encoding a hydroxylase involved in the biosynthesis of host-selective ACR-toxin in the rough lemon pathotype of Alternaria alternata.
The rough lemon pathotype of Alternaria alternata produces host-selective ACR-toxin and causes Alternaria leaf spot disease of the rootstock species rough lemon (Citrus jambhiri) and Rangpur lime (C. limonia). Genes controlling toxin production were localized to a 1.5-Mb chromosome carrying the ACR-toxin biosynthesis gene cluster (ACRT) in the genome of the rough lemon pathotype. A genomic BAC clone containing a portion of the ACRT cluster was sequenced which allowed identification of three open reading frames present only in the genomes of ACR-toxin producing isolates. We studied the functional role of one of these open reading frames, ACRTS1 encoding a putative hydroxylase, in ACR-toxin production by homologous recombination-mediated gene disruption. There are at least three copies of ACRTS1 gene in the genome and disruption of two copies of this gene significantly reduced ACR-toxin production as well as pathogenicity; however, transcription of ACRTS1 and production of ACR-toxin were not completely eliminated due to remaining functional copies of the gene. RNA-silencing was used to knock down the remaining ACRTS1 transcripts to levels undetectable by reverse transcription-polymerase chain reaction. The silenced transformants did not produce detectable ACR-toxin and were not pathogenic. These results indicate that ACRTS1 is an essential gene in ACR-toxin biosynthesis in the rough lemon pathotype of A. alternata and is required for full virulence of this fungus.
Faculty of Agriculture, Kagawa University, Miki, Kagawa, Japan.
Yuriko
Y
Izumi
Eri
E
Kamei
Yoko
Y
Miyamoto
Kouhei
K
Ohtani
Akira
A
Masunaka
Takeshi
T
Fukumoto
Kenji
K
Gomi
Yasuomi
Y
Tada
Kazuya
K
Ichimura
Tobin L
TL
Peever
Kazuya
K
Akimitsu
D000528:Alternaria / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity*; D002957:Citrus / Q000382:microbiology*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D009183:Mycotoxins / Q000096:biosynthesis* / Q000235:genetics; D010935:Plant Diseases / Q000382:microbiology*; D014774:Virulence
D005656:Fungal Proteins; D009183:Mycotoxins