Sequence characterization of four putative membrane‐associated proteins from sweet potato little leaf strain V4 phytoplasma

Abstract

To increase understanding of the genetic architecture of phytoplasmas, a random clone (pH80) of the sweet potato little leaf strain‐V4 (SPLL‐V4) phytoplasma and the glucose‐inhibited division protein A (gidA) gene were analysed. Clone pH80 and the gidA gene are located in a 100‐kb region near the putative origin of replication. Three ORFs were identified within the pH80 random clone, encoding the proteins PotB, PotC and PotD, which form part of an ABC transport system for polyamine import. Sequence data were supported by structural analysis which indicated that SPLL‐V4 PotB and PotC were integral membrane proteins, and PotD was a substrate‐binding, surface‐exposed membrane protein. The gidA gene in the SPLL‐V4 phytoplasma was also putatively identified as a membrane protein. The complete gidA gene sequences were characterized for the tomato big bud and SPLL‐V4 phytoplasmas. The proteins identified here were found to share high similarity with those recently identified in the onion yellows phytoplasma genome. Both the gidA and polyamine transport operons are believed to be associated with DNA replication.