Evil twins: attenuation of karrikin and strigolactone signaling by antagonistic paralogs

Abstract:
Subfunctionalization and neofunctionalization of paralogs produced by gene duplication are common evolutionary processes that create proteins with specialized or novel functions. For example, KAI2 proteins that function as receptors for karrikin-derived signals in many land plants have evolved into strigolactone receptors in root parasitic plants through extensive gene duplication and neofunctionalization. A less appreciated fate of duplicated genes is the formation of antagonistic paralogs, which have opposing functions. In karrikin and strigolactone signaling, alpha/beta-hydrolase receptors KAI2 and D14, respectively, work with the F-box protein MAX2 to target transcriptional regulator proteins in the SMAX1-like (SMXL) family for polyubiquitination and degradation. We found that a subset of SMXL proteins that are resistant to MAX2-mediated degradation inhibit strigolactone-induced degradation of other SMXL proteins, limiting strigolactone responses. We have also observed a set of KAI2 proteins in parasitic plants that inhibit rather than promote strigolactone responses. Their dominant-negative effects may be useful during chemiosmotic growth toward a host or for tuning host-specificity in strigolactone perception. Finally, we have found that DLK2, a paralog of KAI2 and D14, imposes feedback inhibition of karrikin signaling likely by hydrolyzing KAI2 ligands without initiating signal transduction. Thus, dominant or dominant-negative mutations can be a feature rather than a bug during gene evolution, particularly for fine-tuning signaling.

About the Speaker:
Dave Nelson received his PhD in Genetics in 2006 from the University of Wisconsin-Madison, where he worked with Mike Sussman. As a postdoctoral researcher with Steven Smith at the University of Western Australia and Winslow Briggs at the Carnegie Institution for Science, he pioneered the genetics of karrikin signaling and established an unexpected link between karrikins and strigolactones. He became an Assistant Professor at the University of Georgia in 2011, before moving to the University of California, Riverside in 2016. He is now a Professor in the Department of Botany and Plant Sciences. His lab studies how plants make and perceive strigolactones and karrikin-derived signals, and how these mechanisms have evolved.

Contact

  Jesse Lasky
  jrl35@psu.edu