About this Research Topic
The plant specific class of hybrid proline- or glycine-rich proteins (HyP/GRP) are putative cell-wall/plasma membrane associated proteins. Their coding regions form gene families, and even small plant genomes such as that of Arabidopsis thaliana contain approximately 30 HyP/GRP genes. The mature proteins have two distinct domains: a hydrophilic proline-rich or glycine-rich repetitive domain (PRD or GRP, respectively) at the N-terminus, and a hydrophobic domain with eight cysteine residues in a specific order called the eight-cysteine motif (8CM) at the C-terminus. The unprocessed proteins contain putative signal peptides at the immediate N-terminus for presumed secretion into the cell wall and/or cell membrane. While they share similarity with lipid transfer proteins and protease inhibitors, the specific cysteine spacing and hydrophobicity of the C-terminus makes them a distinct class of enigmatic proteins. Although a few HyP/GRPs were implicated to play auxiliary and pleiotropic roles in embryogenesis, germination, and in response to biotic and abiotic stresses, the overall function of this gene family remains enigmatic. This research topic is thus focused on addressing numerous unanswered questions to understand what these proteins do during plant development. Questions include, but are not limited to: How do HyP/GRP help protect plants against freezing, drought, and salinity? What is their role during embryogenesis? Do they participate in endosperm cell weakening during germination, and if so, how? Do they regulate cell elongation, and if so, how? Are they involved in programmed cell death during pathogen attack? Do they have distinct or redundant functions? What is the role of posttranscriptional modifications? What are their precise subcellular localizations? Are there distinct subfamilies with redundant functions or do they work together to achieve pleiotropic effects? All types of articles (original research, method, opinion and review) that provide new insights into these fascinating questions are welcomed.
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