Timothy Lo: "Sibling Rivalry: Functional Diversification of a Pseudomonas syringae Virulence Protein Family" and Francisco Rodrigues: "Examining an Essential Role for an Arf-GAP in Cell Division"

Timothy Lo: Containing an armory of virulence proteins, termed type III secreted effectors (T3SEs), the bacterial plant pathogen Pseudomonas syringae infects a wide variety of plant hosts, including tomato and the model plant organism Arabidopsis thaliana. T3SEs are crucial for P. syringae pathogenesis and function primarily to suppress plant immunity. More than 60 families of T3SEs have been identified in P. syringae, including the HopF family of T3SEs. With the increasing number of sequenced P. syringae genomes, the HopF family now contains over forty different family members. Research has predominantly focused on two family members: HopF2 from the tomato/Arabidopsis pathogen P. syringae pathovar tomato DC3000 and HopF1 from the bean pathogen P. syringae pathovar phaseolicola 1449B. Research on the function of these two T3SEs has revealed that HopF2PtoDC3000 can promote virulence in Arabidopsis, while HopF1Pph1449B promotes virulence in beans; yet the function of the remaining HopF family members remains unknown. To investigate the functional differences within this diverse T3SE family, phylogenetic analyses were conducted along with functional characterization on Arabidopsis, beans and soybeans. This analysis revealed that HopF2 from P. syringae pathovar tomato T1 displayed markedly different functional phenotypes compared with the well characterized HopF2PtoDC3000 highlighting the functional diversification within a single T3SE family. Furthermore, the functional difference between these two closely related T3SEs influences the ability of P. syringae to infect Arabidopsis, emphasizing the contribution of T3SE functional diversification to pathogen host range. Francisco Rodrigues: Regulation of the plasma membrane is essential to ensure proper division of mitotic cells. However, it is still unclear how dividing cells supply membrane to the enclosing furrow. Here, we use the early Drosophila embryo to investigate the role of the ArfGAP Asap during cell division. ArfGAPs are key regulators of membrane trafficking via Arf G protein signaling. We show that the Drosophila Asap is required to promote growth of ingressing metaphase furrows. Potential mechanisms of how this is achieved will be discussed.