Calcium reservoirs in the cell wall: AGPs driving reproductive success
Jessy Silva (Portugal)1 2; Maria João Ferreira (Portugal)1; Paul Dupree (UK)3; Matthew R. Tucker (Australia)4; Maria Manuela Ribeiro Costa (Portugal)5; Sílvia Coimbra (Portugal)1;
1 - LAQV/REQUIMTE, Department of Biology, Faculty of Sciences, University of Porto, Porto, Portugal; 2 - Department of Biology, University of Minho, Campus of Gualtar, Braga, Portugal; 3 - Department of Biochemistry, University of Cambridge, Cambridge, UK; 4 - School of Agriculture, Food and Wine, University of Adelaide, Waite Campus, Urrbrae, SA, Australia; 5 - Centre of Molecular and Environmental Biology (CBMA), Department of Biology, University of Minho, Campus of Gualtar, Braga, Portugal;
Keywords: Arabinogalactan-proteins (AGPs)-Ca2+ binding; Glucuronic acid (GlcA) modification; Arabidopsis double fertilization;
Abstract Topics: Theme 4: Arabinogalactan Proteins
Type of Presentation: Oral Communication

Abstract text: Arabinogalactan-proteins (AGPs) are highly glycosylated cell wall proteins essential for plant reproduction. AGPs are extensively decorated with 90% of arabinogalactan polysaccharides composed of arabinose and galactose, and minor sugars such as glucuronic acid (GlcA), fucose, and rhamnose. AGPs can bind and store calcium (Ca2+) via GlcA residues in a pH-dependent manner, potentially serving as Ca2+ reservoirs in the apoplast. As the sugar moiety is crucial for AGP function, we explored the role of the glucuronosyltransferases (GLCATs), responsible for GlcA presence on AGPs, during Arabidopsis reproduction. Previously, glcat14a glcat14b glcat14d mutants showed a reduction in methyl GlcA substitution in AGP-enriched preparations holding less Ca2+ than wild-type plants in vitro.

Here we report that Ca2+ binding by AGPs is required for successful double fertilisation in Arabidopsis. Analysis of glcat14a glcat14b glcat14d triple mutants revealed reduced seed set due to abortion of pollen grains, which lacked cytoplasmic content and an intine layer, confirmed by absence of cellulose, resembling AGP-deficient mutants. When grown under Ca2+-deficient conditions, GLCAT mutants showed exacerbated reproductive defects attenuated under standard Ca2+ conditions. Our findings establish a functional requirement for GlcA-mediated Ca2+ binding by AGPs and support their role as apoplastic Ca2+ stores essential for reproductive success in plants.