PECTIN METHYLESTERASE48 Is Involved in Arabidopsis Pollen Grain Germination

• Published in: Plant physiology (Bethesda) Vol. 167; no. 2; pp. 367 - 380
• Main Authors: Leroux, Christelle, Bouton, Sophie, Kiefer-Meyer, Marie-Christine, Fabrice, Tohnyui Ndinyanka, Mareck, Alain, Guénin, Stéphanie, Fournet, Françoise, Ringli, Christoph, Pelloux, Jérôme, Driouich, Azeddine, Lerouge, Patrice, Lehner, Arnaud, Mollet, Jean-Claude
• Format: Journal Article
• Language: English
• Published: United States American Society of Plant Biologists 01-02-2015; Oxford University Press ; American Society of Plant Biologists
• Subjects: American culture; Arabidopsis - drug effects; Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis - growth & development; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Biochemistry; Biochemistry, Molecular Biology; Biology; Biotechnology; Calcium - pharmacology; Carboxylic Ester Hydrolases - genetics; Carboxylic Ester Hydrolases - metabolism; Cell Behavior; CELL BIOLOGY; Cell growth; Cell walls; Cellular Biology; Chemical Sciences; Culture Media - pharmacology; Development Biology; Esterification - drug effects; Gametogenesis; Gene Expression Regulation, Plant - drug effects; Genomics; Germination; Grains; Homozygote; Life Sciences; Molecular biology; Molecular Networks; Mutation - genetics; Organ Specificity - drug effects; Organ Specificity - genetics; Pectins - metabolism; Phenotype; Phytopathology and phytopharmacy; Plant breeding; Plant cells; Plants; Pollen; Pollen - enzymology; Pollen - genetics; Pollen - growth & development; Pollen Tube - drug effects; Pollen Tube - metabolism; Pollen tubes; Polymers; Reverse Transcriptase Polymerase Chain Reaction; Subcellular Processes; Vegetal Biology
• ISSN: 0032-0889; 1532-2548; 1532-2548
• DOI: 10.1104/pp.114.250928

Germination of pollen grains is a crucial step in plant reproduction. However, the molecular mechanisms involved remain unclear. We investigated the role of PECTIN METHYLESTERASE48 (PME48), an enzyme implicated in the remodeling of pectins in Arabidopsis (Arabidopsis thaliana) pollen. A combination of functional genomics, gene expression, in vivo and in vitro pollen germination, immunolabeling, and biochemical analyses was used on wild-type andAtpme48mutant plants. We showed thatAtPME48is specifically expressed in the male gametophyte and is the second most expressedPMEin dry and imbibed pollen grains. Pollen grains from homozygous mutant lines displayed a significant delay in imbibition and germination in vitro and in vivo. Moreover, numerous pollen grains showed two tips emerging instead of one in the wild type. Immunolabeling and Fourier transform infrared analyses showed that the degree of methylesterification of the homogalacturonan was higher inpme48−/− pollen grains. In contrast, the PME activity was lower inpme48−/−, partly due to a reduction of PME48 activity revealed by zymogram. Interestingly, the wild-type phenotype was restored inpme48−/− with the optimum germination medium supplemented with 2.5 mM calcium chloride, suggesting that in the wild-type pollen, the weakly methylesterified homogalacturonan is a source of Ca²⁺ necessary for pollen germination. Although pollen-specific PMEs are traditionally associated with pollen tube elongation, this study provides strong evidence that PME48 impacts the mechanical properties of the intine wall during maturation of the pollen grain, which, in turn, influences pollen grain germination.