Biological Characteristics and Molecular Mechanism of Fludioxonil Resistance in Botrytis cinerea From Henan Province of China.

The gray mold caused by Botrytis cinerea has a significant impact on tomato production throughout the world. Although the synthetic fungicide fludioxonil can effectively control B. cinerea, there have been several reports of resistance to this fungicide. This study indicated that all of the fludioxonil-resistant strains tested, including one field-resistant isolate and four laboratory strains, had reduced fitness relative to sensitive isolates. In addition to having reduced growth, sporulation, and pathogenicity, the resistant strains were more sensitive to osmotic stress and had significantly (P < 0.05) higher peroxidase activity. BOs1, a kinase in the high-osmolarity glycerol stress response signal transduction pathway, is believed to harbor mutations related to fludioxonil resistance. Sequence analysis of their BOs1 sequences indicated that the fludioxonil-resistant field isolate, XXtom1806, had four point mutations resulting in four amino acid changes (I365S, S531G, T565N, and T1267A) and three amino acids (I365S, S531G, and T565N) in the histidine kinases, adenylyl cyclases, methyl-accepting chemotaxis receptors, and phosphatases domain, which associated with fludioxonil binding. Similarly, two of the laboratory strains, XXtom-Lab1 and XXtom-Lab4, had three (Q846S, I1126S, and G415D) and two (P1051S and V1241M) point mutations, respectively. A third strain, XXtom-lab3, had a 52-bp insertion that included a stop codon at amino acid 256. Interestingly, the BOs1 sequence of the fourth laboratory strain, XXtom-lab5, was identical to those of the sensitive isolates, indicating that an alternative resistance mechanism exists. The study also found evidence of positive cross-resistance between fludioxonil and the dicarboximide fungicides procymidone and iprodione, but no cross-resistance was detected with any other fungicides tested, including boscalid, carbendazim, tebuconazole, and fluazinam.

Characterization of 3-Oxacyl-Acyl Carrier Protein Reductase Homolog Genes in Pseudomonas aeruginosa PAO1.

Bacterial 3-oxoacyl-ACP reductase (OAR) catalyzes the 3-oxoacyl-ACP reduction step in the fatty acid synthesis pathway. At least 12 genes in the Pseudomonas aeruginosa genome are annotated as OAR-encoding genes. In this study, we characterized the functions of these genes with biochemical and genetic techniques. With the exception of PA2967, which encodes FabG, an essential protein in fatty acid synthesis, only the PA4389 and PA4786 gene products had OAR activity, and the single deletion of these two genes reduced the ability of P. aeruginosa to produce several specific quorum-sensing (QS) signals. However, PA4389 and PA4786 do not have key roles in fatty acid synthesis. Moreover, although most OAR homologs had no OAR activity, some may function in carbon utilization. The PA3128 product may play a role in the TCA cycle, and PA0182 and PA1470 seem to be required for the utilization of several amino acids. The rest of the OAR homologs have no roles in carbon utilization, but the deletion of one of these genes might affect the production of virulence factors by P. aeruginosa. We conclude that most OAR homolog genes do not encode OAR enzymes, and that these proteins do not function in fatty acid synthesis. IMPORTANCE: We report that although all P. aeruginosa OAR homologs have similar structures and the conserved catalytic triad of the bacterial OAR enzymes, only a few OAR homologs have OAR activity.