Abstract
Centaurium erythraea (centaury) is a medicinal plant with exceptional developmental plasticity in vitro and vigorous, often spontaneous, regeneration via shoot organogenesis and somatic embryogenesis, during which arabinogalactan proteins (AGPs) play an important role. AGPs are highly glycosylated proteins belonging to the super family of O-glycosylated plant cell surface hydroxyproline-rich glycoproteins (HRGPs). HRGPs/AGPs are intrinsically disordered and not well conserved, making their homology-based mining ineffective. We have applied a recently developed pipeline for HRGP/AGP mining, ragp, which is based on machine learning prediction of proline hydroxylation, to identify HRGP sequences in centaury transcriptome and to classify them into motif and amino acid bias (MAAB) classes. AGP sequences with low AG glycomotif representation were also identified. Six members of each of the three AGP subclasses, fasciclin-like AGPs, receptor kinase-like AGPs and AG peptides, were selected for phylogenetic and expression analyses. The expression of these 18 genes was recorded over 48 h following leaf mechanical wounding, as well as in 16 tissue samples representing plants from nature, plants cultivated in vitro, and developmental stages during shoot organogenesis and somatic embryogenesis. None of the selected genes were upregulated during both wounding recovery and regeneration. Possible functions of AGPs with the most interesting expression profiles are discussed.
Highlights
Hydroxyproline-rich glycoproteins (HRGPs) are a super family of plant cell surfaceO-linked glycoproteins
The ragp pipeline incorporates N-sp prediction based on majority vote among Phobius 1.01, SignalP 4.1 and TargetP 1.1
Our results confirm that wounding causes changes in arabinogalactan proteins (AGPs)’ expression profiles, but a more systematic approach is required to clarify the role of AGPs such as CeAGP6 and CeAGP7 in wound and healing responses
Summary
They are embedded into the cellulose/hemicellulose and pectic polysaccharide networks of the cell wall and are involved in the cell dynamics through diverse functions in growth and development, environmental sensing, signaling and defense [1,2,3]. Based on the patterns of proline hydroxylation and subsequent glycosylation, HRGPs are traditionally classified into three families: the highly glycosylated arabinogalactan proteins (AGPs), the moderately glycosylated extensins (EXTs) and the lightly glycosylated proline-rich proteins (PRPs). The distinction among these groups is often blurred, since many sequences have shared characteristics. Among the three classical HRGP families, AGPs have attracted considerable attention due to their structural diversity and roles in many physiological processes [5]
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