Regulation of <i>corA</i>, the Magnesium, Nickel, Cobalt Transporter, and Its Role in the Virulence of the Soft Rot Pathogen, <i>Pectobacterium versatile</i> Strain Ecc71

<i>Pectobacterium versatile</i> (formally <i>P. carotovorum</i>) causes disease on diverse plant species by synthesizing and secreting copious amount of plant-cell-wall-degrading exoenzymes including pectate lyases, polygalacturonases, cellulases, and proteases. Exoenzyme production and virulence are controlled by many factors of bacterial, host, and environmental origin. The ion channel forming the magnesium, nickel, and cobalt transporter CorA is required for exoenzyme production and full virulence in strain Ecc71. We investigated CorA’s role as a virulence factor and its expression in <i>P</i>. <i>versatile</i>. Inhibiting the transport function of CorA by growing a CorA⁺ strain in the presence of specific CorA inhibitor, cobalt (III) hexaammine (Co (III)Hex), has no effect on exoenzyme production. Transcription of <i>pel-1</i>, encoding a pectate lyase isozyme, is decreased in the absence of CorA, suggesting that CorA influences exoenzyme production at the transcriptional level, although apparently not through its transport function. CorA⁻ and CorA⁺ strains grown in the presence of Co (III)Hex transcriptionally express <i>corA</i> at higher levels than CorA⁺ strains in the absence of an inhibitor, suggesting the transport role of <i>corA</i> contributes to autorepression. The expression of <i>corA</i> is about four-fold lower in HrpL⁻ strains lacking the <i>hrp</i>-specific extracytoplasmic sigma factor. The <i>corA</i> promoter region contains a sequence with a high similarity to the consensus Hrp box, suggesting that <i>corA</i> is part of Hrp regulon. Our data suggest a complex role, possibly requiring the physical presence of the CorA protein in the virulence of the <i>Pectobacterium versatile</i> strain Ecc71.