An Exo-Polygalacturonase Pgc4 Regulates Aerial Hyphal Growth and Virulence in <i>Fusarium oxysporum</i> f. sp. <i>cubense</i> race 4

• Main Authors: Zhangyong Dong, Mei Luo, Zhenzhong Wang
• Format: Article
• Language: English
• Published: MDPI AG 2020-08-01
• Series: International Journal of Molecular Sciences
• Subjects: polygalacturonase; virulence; <i>Fusarium oxysporum</i> f. sp. <i>cubense</i> race 4
• Online Access: https://www.mdpi.com/1422-0067/21/16/5886
• ISSN: 1661-6596; 1422-0067

<i>Fusarium oxysporum</i> f. sp. <i>cubense</i> 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 <i>pgc4</i> 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 <i>K</i>m and <i>V</i>max 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 <i>Pichia pastoris</i> 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 Foc4Δ<i>pgc4</i> 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.