Characterization of the phosphoproteome of mature Arabidopsis pollen.
Successful pollination depends on cell-cell communication and rapid cellular responses. In Arabidopsis, the pollen grain lands on a dry stigma, where it hydrates, germinates and grows a pollen tube that delivers the sperm cells to the female gametophyte to effect double fertilization. Various studies have emphasized that a mature, dehydrated pollen grain contains all the transcripts and proteins required for germination and initial pollen tube growth. Therefore, it is important to explore the role of post-translational modifications (here phosphorylation), through which many processes induced by pollination are probably controlled. We report here a phosphoproteomic study conducted on mature Arabidopsis pollen grains with the aim of identifying potential targets of phosphorylation. Using three enrichment chromatographies, a broad coverage of pollen phosphoproteins with 962 phosphorylated peptides corresponding to 598 phosphoproteins was obtained. Additionally, 609 confirmed phosphorylation sites were successfully mapped. Two hundred and seven of 240 phosphoproteins that were absent from the PhosPhAt database containing the empirical Arabidopsis phosphoproteome showed highly enriched expression in pollen. Gene ontology (GO) enrichment analysis of these 240 phosphoproteins shows an over-representation of GO categories crucial for pollen tube growth, suggesting that phosphorylation regulates later processes of pollen development. Moreover, motif analyses of pollen phosphopeptides showed an over-representation of motifs specific for Ca²⁺/calmodulin-dependent protein kinases, mitogen-activated protein kinases, and binding motifs for 14-3-3 proteins. Lastly, one tyrosine phosphorylation site was identified, validating the TDY dual phosphorylation motif of mitogen-activated protein kinases (MPK8/MPK15). This study provides a solid basis to further explore the role of phosphorylation during pollen development.
Centre for Model Organism Proteomes, University of Zürich, Zürich, Switzerland.
Pururawa
P
Mayank
Jonas
J
Grossman
Samuel
S
Wuest
Aurélien
A
Boisson-Dernier
Bernd
B
Roschitzki
Paolo
P
Nanni
Thomas
T
Nühse
Ueli
U
Grossniklaus
D048948:14-3-3 Proteins / Q000378:metabolism; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000737:chemistry / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D030541:Databases, Genetic; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008969:Molecular Sequence Data; D009928:Organ Specificity; D010748:Phosphopeptides / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D010750:Phosphoproteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D010766:Phosphorylation; D011058:Pollen / Q000737:chemistry / Q000254:growth & development / Q000378:metabolism*; D053205:Pollen Tube / Q000254:growth & development / Q000378:metabolism; D054817:Pollination; D011499:Protein Processing, Post-Translational; D020543:Proteome; D059467:Transcriptome
D048948:14-3-3 Proteins; D029681:Arabidopsis Proteins; D010748:Phosphopeptides; D010750:Phosphoproteins; D020543:Proteome; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C558242:MPK8 protein, Arabidopsis; D020928:Mitogen-Activated Protein Kinases