Understanding the evolution of Sap54, a phyllody associated phytoplasma effector gene through phylogenetic network analysis

Abstract

Phytoplasmas, a large group of plant pathogenic bacteria, are transmitted from plant to plant by phloem feeding insects. They are associated with a wide variety of symptoms like stunting, development of numerous tiny shoots having small leaves (witches’ broom), yellowing, greening of flower organs (virescence), phyllody. It seems that these symptoms derive from effector molecules secreted from plant tissues adjacent to the phloem. Several effector molecules like SAP54, SAP11, SAP21 and TENGU have been identified in phytoplasmas. Among them, SAP54 (homolog of phyllogen, PHYL-1 gene) is reported as polymorphic compared to other effectors. The present study was conducted to verify the diversity and evolution of this phyllogen gene in various ribosomal phytoplasma groups with the help of phylogenetic networking. The network depicts evidence of multiple reticulation events as the PHYL-1 gene has undergone horizontal gene transfers and recombination events. It can also be concluded from the network that phyl-A group is predominant among the phytoplasmas under study and the horizontal gene transfers seems to have played a significant role in its evolution and diversification.