Ph.D. Program in Plant Molecular Biology

Friday Seminar by Mr. Vishal Vashisth

Speaker  :    Mr. Vishal Vashisth
Topic        :  "PGAP1 mediated remodelling of GPI-APs regulates self- incompatibility (SI) response in angiosperms".
Date & Time : April 8, 2022 at 3.30PM via online mode
Category: Research

PGAP1 mediated remodelling of GPI-APs regulates self- incompatibility (SI) response in angiosperms


Vishal Vashisth

Glycosylphosphatidylinositol-anchored proteins (GPI-APs), tethered to the outer leaflet of plasma membrane in eukaryotes, are reported to be key regulators of plethora of biological processes. Biosynthesis and addition of GPI anchors to its target proteins takes place in the ER. GPI anchoring is one of the most important post-translational modifications of proteins and is crucial for the biosynthesis and targeting of the GPI anchored proteins to the outer leaflet of plasma membrane in eukaryotes. Defective biosynthesis, targeting and/or remodeling of GPI-APs strongly affect plant development.  Self-incompatibility (SI) in flowering plants is one of the most important system to prevent inbreeding and promote outbreeding. SI involves recognition of self/non-self-pollen and rejection of self-pollen. SI is controlled by single polymorphic-multiallelic locus, the S-locus.
Interestingly, mutants of Highlander (HLD1/AtPGAP1), an ortholog of animals post-GPI attachment to proteins 1 (PGAP1) completely abolished SI response in self-incompatible Arabidopsis lines (At-SI) co-expressing Papaver pollen and pistil S determinants, PrpS and PrsS, respectively, suggesting its crucial role in SI response. PGAP1 functions as a GPI-inositol-deacylase and removes the acyl chain from the GPI anchors after its attachment to its target proteins. Papaver ortholog of PGAP1, PrPGAP1 induces pollen tube growth inhibition and cell death in Papaver, suggesting its conserved role in SI response. AtPGAP1 regulates SI irrespective of the S-alleles involved, evidenced by SI suppression in plants expressing an alternative pair of cognate S-alleles, PrpS and PrsS. Besides reproductive context, the AtPGAP1 induces ectopic ‘SI-like PCD’’ in Arabidopsis roots. One of the key features of PGAP1 is the presence of a catalytic serine-containing motif, V***GHSMGG, in the PGAP1- like domain and highly conserved across all eukaryotes, and also present around serine 218 in AtPGAP1. GPI-inositol deacylase function of AtPGAP1 is essential for SI in Angiosperms. Mutations in the catalytic core of AtPGAP1 phenocopy hld phenotype/SI suppression. In-vivo, GPI-inositol deacylation activity of AtPGAP1 is critical for the proper cleavage and release of membrane bound GPI-APs, as PLC cleaves only deacylated GPI-APs. Therefore, AtPGAP1 regulates SI possibly by affecting PLC mediated cleavage & release of GPI-APs, that is otherwise resistant to cleavage in atgap1 mutants. Thus, mammalian PGAP1 orthologs, AtPGAP1 & PrPGAP1, mediated remodeling of GPI-APs regulates SI responses in Arabidopsis & Papaver rhoeas, respectively.

Suggested readings:

  • Lin, Zongcheng, et al. "The Papaver rhoeas S determinants confer self-incompatibility to Arabidopsis thaliana in planta." Science 350.6261 (2015): 684-687.
  • Lin, Zongcheng, et al. "Ectopic expression of a self-incompatibility module triggers growth arrest and cell death in vegetative cells." Plant Physiology 183.4 (2020): 1765-1779.
  • Lin, Zongcheng, et al. "Self-incompatibility requires GPI anchor remodeling by the poppy PGAP1 ortholog HLD1." Current Biology (2022)