Unlike wild-type strain 3937, which fully macerates inoculated Saintpaulia plants, HmpX mutants produce necrotic lesions or no symptoms. The gene was sequenced and the corresponding protein sequence analysed. We show that HmpX belongs to a family of flavohaemoproteins (HMP), previously identified in two yeasts and in . Comparisons of protein sequences at the secondary structure level by hydrophobic cluster analysis have shown that HmpX possesses two functional regions, a haemoglobin domain in its N-terminal part and a flavin reductase domain in its C-terminal part. In an HmpX strain, the synthesis of pectate lyases, which are pathogenicity determinants in , was reduced in conditions of low oxygen tension. Using fusion in , it was shown that transcription was induced in coculture with tobacco cells. A putative function for HmpX is discussed.


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