Carter, M. E., Carpenter, S. C., Dubrow, Z. E., Sabol, M. R., Rinaldi, F. C., Lastovetsky, O. A., ... & Bogdanove, A. J. (2020). A TAL effector-like protein of an endofungal bacterium increases the stress tolerance and alters the transcriptome of the host. Proceedings of the National Academy of Sciences, 117(29), 17122-17129.
Morgan Carter et al. (2020)'s article "A TAL effector-like protein of an endofungal bacterium increases the stress tolerance and alters the transcriptome of the host" suggests that the TAL-like effector molecules secretable via the T3SS by Mycetohabitans bacteria are nuclear-localizing, but have diverse functions. Carter uses a variety of functional assays and mutants to tease out the role and (trans)localization of the TAL-like Btl19-13 effector within the Rhizopus-Mycetohabitans symbiosis, revealing its role in membrane stress (i.e. SDS%) tolerance. The authors sought to reveal similarities or differences between these Btl proteins and the TAL effectors of plant pathogenic bacteria in order to better understand the establishment and maintenance of endosymbiosis.
Does this imply the HGT events from plant pathogenic Xanthomonas sp., given the presence of the plant hormone-promoted gene control via HrpB? Were they descendents of an ancestor with TALs that then diversified, or did some ancestral bacterium get TAL-like effector from Xanthomonas? I believe higher oligomeric states have been implicated in the function of these TAL effectors [1]. Is there potentially an effect of higher oligomeric states that may have been missed here? Maybe not, because why wouldn't that have occurred if necessary?
1. Richter, I., Uzum, Z., Stanley, C. E., Moebius, N., Stinear, T. P., Pidot, S. S., ... & Hertweck, C. (2020). Secreted TAL effectors protect symbiotic bacteria from entrapment within fungal hyphae. bioRxiv.