Abstract
Fusarium oxysporum f. sp. cubense race 4 (Foc4) causes Fusarium wilt that affects banana plants, and hence, the molecular mechanisms of its virulence need to be investigated. We purified an exo-polygalacturonase (exo-PG), Pgc4, from Foc4. Pgc4 has an apparent molecular weight of 50.87 kDa based on sodium dodecyl sulphate–polyacrylamide gel electrophoresis. We further performed its sequence analysis and biochemical characterization. The two pgc4 genes encoding Pgc4 from Foc4 and Foc1 were 1434 bp in length and encoded 477 amino acids with differences, due to some nucleotide differences between the two. The Km and Vmax values of Pgc4 purified from Foc4 were determined to be 0.45 mg/mL and 105.26 Units·mg·protein−1 ·min−1, respectively. The recombinant proteins, r-Foc1-Pgc4 and r-Foc4-Pgc4, were expressed and purified from Pichia pastoris and showed optimal Pgc4 activity at 55 °C and pH 4.0; both could induce tissue maceration and necrosis in the “Guangfen-1” and “Baxi” varieties of banana but to a different extent. Phenotypic assays and complementation analyses revealed that, compared to the wild-type, the generated Foc4Δpgc4 mutant strain showed a lower aerial hyphal growth, grew slower, and had a reduced virulence. Therefore, our results demonstrate the function of Pgc4 as a pathogenicity factor of Foc4.
Highlights
Fusarium oxysporum can induce the vascular wilt disease in many important cash crops and is one of the most common and important Fusarium species worldwide [1]
The Fusarium wilt of bananas caused by F. oxysporum f. sp. cubense is a serious threat to global banana (Musa spp.) production [2]
Many efforts have been made to improve the resistance of banana to Foc, the number of available varieties of banana that are resistant to Fusarium wilt disease are still limited
Summary
Fusarium oxysporum can induce the vascular wilt disease in many important cash crops and is one of the most common and important Fusarium species worldwide [1]. The Fusarium wilt of bananas caused by F. oxysporum f. Cubense (Foc) were divided into three races based on the banana cultivars they infect: race 1 (Foc1) infects the “Gros Michel” (AAA) and “Silk” (AAB) cultivars, race 2 (Foc2) causes disease only in the “Bluggoe” (ABB) cultivar, and race 4 (Foc4) infects most banana cultivars [3]. Many efforts have been made to improve the resistance of banana to Foc, the number of available varieties of banana that are resistant to Fusarium wilt disease are still limited. There are no banana varieties that are completely resistant to Foc, and there are no suitable management strategies for Fusarium wilt plants infected by Foc. The pathogenesis of the disease has not been fully defined and needs to be studied further
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