Characterization of the fusaric acid gene cluster in Fusarium fujikuroi

Abstract

The "bakanae" fungus Fusarium fujikuroi is a common pathogen of rice and produces a variety of mycotoxins, pigments, and phytohormones. Fusaric acid is one of the oldest known secondary metabolites produced by F. fujikuroi and some other Fusarium species. Investigation of its biosynthesis and regulation is of great interest due to its occurrence in cereal-based food and feed. This study describes the identification and characterization of the fusaric acid gene cluster in F. fujikuroi consisting of the PKS-encoding core gene and four co-regulated genes, FUB1-FUB5. Besides fusaric acid, F. fujikuroi produces two fusaric acid-like derivatives: fusarinolic acid and 9,10-dehydrofusaric acid. We provide evidence that these derivatives are not intermediates of the fusaric acid biosynthetic pathway, and that their formation is catalyzed by genes outside of the fusaric acid gene cluster. Target gene deletions of all five cluster genes revealed that not all of them are involved in fusaric acid biosynthesis. We suggest that only two genes, FUB1 and FUB4, are necessary for the biosynthesis. Expression of the FUB genes and production of fusaric acid and the two derivatives are favored under high nitrogen. We show that nitrogen-dependent expression of fusaric acid genes is positively regulated by the nitrogen-responsive GATA transcription factor AreB, and that pH-dependent regulation is mediated by the transcription factor PacC. In addition, fusaric acid production is regulated by two members of the fungal-specific velvet complex: Vel1 and Lae1. In planta expression studies show a higher expression in the favorite host plant rice compared to maize.

Fusarins and Fusaric Acid in Fusaria

“…In F. fujikuroi , FUB1 has also been deleted resulting in total loss of FA production. However, deletion of the other four assumed biosynthetic genes, FUB2 -FUB5 , revealed that all mutants except for Δ(Delta) FUB4 still produced FA suggesting that only two of the co-regulated genes, FUB1 and FUB4 , are responsible for FA biosynthesis [ 14 ]. To confi rm this unexpected result, a multiple Δ(Delta) FUB 2-5 deletion mutant expressing only the PKS-encoding gene FUB1 , was transformed with FUB4 .…”

“…To confi rm this unexpected result, a multiple Δ(Delta) FUB 2-5 deletion mutant expressing only the PKS-encoding gene FUB1 , was transformed with FUB4 . The generated strains containing only the two cluster genes FUB1 and FUB4 were able to produce FA-though in lower amounts than the wild type [ 14 ].…”

“…As the polyketide gene cluster responsible for FA biosynthesis has been recently identifi ed in F. verticillioides (FVEG_12523-FVEG_12519) ( [ 1 ]) and F. fujikuroi [ 14 ] the biosynthetic pathway can be studied now in more detail by using FUB gene deletion and overexpression mutants. Based on the data known so far, Niehaus et al [ 14 ] showed that only two of the fi ve co-regulated genes in the FA cluster are sufficient for FA production.…”

“…Thus, fusarinolic acid [ 111 , 112 ] and dehydrofusaric acid [ 113 ] are found together with FA in cultures of Gibberella fujikuroi [ 112 ], F. fujikuroi [ 14 ] or F. nygamai where they occur together with their methyl esters [ 13 ]. 10,11-dihydroxyfusaric acid and diacid of FA have been identifi ed in a Fusarium moniliforme strain [ 12 ].…”

Rapid Detection Method for Fusaric Acid-producing Species of Fusarium by PCR

“…FA F. verticillioides, F. crookwellense, F. subglutinans, F. sambucinum, F. napiforme, F. oxysporum, F. solani, F. proliferatum, F. fujikuroi (Bacon , 1996;Niehaus , 2014 (Brown , 2012;2015;Niehaus , 2014 (Fig. 1).…”