Abstract
Pollination in species with dry stigmas begins with the hydration of desiccated pollen grains on the stigma, a highly regulated process involving the proteins and lipids of the pollen coat and stigma cuticle. Self-incompatible species of the Brassicaceae block pollen hydration, and while the early signaling steps of the self-incompatibility response are well studied, the precise mechanisms controlling pollen hydration are poorly understood. Both lipids and proteins are important for hydration; loss of pollen coat lipids and proteins results in defective or delayed hydration on the stigma surface. Here, we examine the role of the pollen coat protein extracellular lipase 4 (EXL4), in the initial steps of pollination, namely hydration on the stigma. We identify a mutant allele, exl4-1, that shows a reduced rate of pollen hydration. exl4-1 pollen is normal with respect to pollen morphology and the downstream steps in pollination, including pollen tube germination, growth, and fertilization of ovules. However, owing to the delay in hydration, exl4-1 pollen is at a disadvantage when competed with wild-type pollen. EXL4 also functions in combination with GRP17 to promote the initiation of hydration. EXL4 is similar to GDSL lipases, and we show that it functions in hydrolyzing ester bonds. We report a previously unknown function for EXL4, an abundant pollen coat protein, in promoting pollen hydration on the stigma. Our results indicate that changes in lipid composition at the pollen–stigma interface, possibly mediated by EXLs, are required for efficient pollination in species with dry stigmas.
Similar content being viewed by others
References
Akoh CC, Lee G, Liaw Y, Huang T, Shaw J (2004) GDLS family of serine esterases/lipases. Prog Lipid Res 43:534–552
Alonso JM et al (2003) Genome-wide insertional mutagenesis of Arabidopsis thaliana. Science 301:653–657
Brick DJ, Brumlik MJ, Buckley JT, Cao J, Davies PC, Misra S, Tranbarger TJ, Upton C (1995) A new family of lipolytic plant enzymes with members in rice, Arabidopsis, and maize. FEBS Lett 377:475–480
Cronquist A (1981) An integrated system of classification of flowering plants. Columbia University Press, Columbia
Davies T (1998) The new automated mass spectrometry deconvolution and identification system (AMDIS). Spectroscopy (Europe) 10:24–27
Dickinson H (1995) Dry stigmas, water and self-incompatibility in Brassica. Sex Plant Reprod 8:1–10
Dixit R, Rizzo C, Nasrallah M, Nasrallah J (2001) The Brassica MIP-MOD gene encodes a functional water channel that is expressed in the stigma epidermis. Plant Mol Biol 45:51–62
Edlund AF, Swanson R, Preuss D (2004) Pollen and stigma structure and function: the role of diversity in pollination. Plant Cell 16:S84–S97
Fiebig A, Mayfield JA, Miley NL, Chau S, Fischer RL, Preuss D (2000) Alterations in CER6, a gene identical to CUT1, differentially affect long-chain lipid content on the surface of pollen and stems. Plant Cell 12:2001–2008
Fiebig A, Kimport R, Preuss D (2004) Comparisons of pollen coat genes across Brassicaceae species reveal rapid evolution by repeat expansion and diversification. Proc Natl Acad Sci USA 101:3286–3291
Helsop-Harrison Y, Shivanna KR (1977) The receptive surface of the angiosperm stigma. Ann Bot 41:1233–1258
Hicks GR, Rojo E, Hong S, Carter DG, Raikhel NV (2004) Germinating pollen has tubular vacuoles, displays highly dynamic vacuole biogenesis, and requires VACUOLESS1 for proper function. Plant Physiol 134:1227–1239
Hiscock SJ, McInnis SM (2003) Pollen recognition and rejection during the sporophytic self-incompatibility response: Brassica and beyond. Trends Plant Sci 8:606–613
Hiscock SJ, Brown D, Gurr SJ, Dickinson HG (2004) Serine esterases are required for pollen tube penetration of the stigma in Brassica. Sex Plant Reprod 15:65–74
Hülskamp M, Kopczak SD, Horejsi TF, Kihl BK, Pruitt RE (1995) Identification of genes required for pollen-stigma recognition in Arabidopsis thaliana. Plant J 8:703–714
Kemp BP, Doughty J (2003) Just how complex is the Brassica S-receptor complex? J Exp Bot 54:157–168
Lee YL, Chen JC, Shaw JF (1997) The thioesterase I of Escherichia coli has arylesterase activity and shows stereospecificity for protease substrates. Biochem Biophys Res Comm 231:452–456
Lolle SJ, Hsu W, Pruitt RE (1998) Genetic analysis of organ fusion in Arabidopsis thaliana. Genetics 149:607–619
Mayfield JA, Preuss D (2000) Rapid initiation of Arabidopsis pollination requires the oleosin-domain protein GRP17. Nat Cell Biol 2:128–130
Mayfield JA, Fiebig A, Johnstone SE, Preuss D (2001) Gene families from the Arabidopsis thaliana pollen coat proteome. Science 292:2482–2485
Nasrallah ME, Liu P, Nasrallah JB (2002) Generation of self-incompatible Arabidopsis thaliana by transfer of two S locus genes from A. lyrata. Science 297:247–249
NIST/EPA/NIH Mass Spectral Library (2005) National Institute of Standards and Technology, Gaithersburg, MD
Preuss D, Lemieux B, Yen G, Davis RW (1993) A conditional sterile mutation eliminates surface components from Arabidopsis pollen and disrupts cell signaling during fertilization. Genes Dev 7:974–985
Pruitt RE, Vielle-Calzada J-P, Ploense SE, Grossniklaus U, Lolle SJ (2000) FIDDLEHEAD, a gene required to suppress epidermal cell interactions in Arabidopsis, encodes a putative lipid biosynthetic enzyme. Proc Natl Acad Sci USA 97:1311–1316
Sarker RH, Elleman CJ, Dickinson HG (1988) Control of pollen hydration in Brassica requires continued protein-synthesis, and glycosylation is necessary for intraspecific incompatibility. Proc Natl Acad Sci USA 85:4340–4344
Swanson R, Edlund AF, Preuss D (2004) Species specificity in pollen-pistil interactions. Ann Rev Genet 38:793–818
Swanson R, Clark T, Preuss D (2005) Expression profiling of Arabidopsis stigma tissue identifies stigma-specific genes. Sex Plant Reprod 18:163–171
Upton C, Buckley JT (1995) A new family of lipolytic enzymes? Trends Biochem Sci 20:178–179
Wolters-Arts M, Lush WM, Mariani C (1998) Lipids are required for directional pollen-tube growth. Nature 392:818–821
Zimmerman P, Hirsch-Hoffmann M, Hennig L, Gruissem W (2004) GENEVESTIGATOR. Arabidopsis microarray database and analysis toolbox. Plant Physiol 136:2621–2632
Acknowledgments
We thank Beverly Chamberlain for assistance with GC-MS and Yimei Chen for assistance with electron microscopy. John Zdenek, Judy Coswell, and Sandra Suwanski provided greenhouse support. Aretha Fiebig, Elizabeth Bray, and Anna Dobritsa gave helpful comments on the manuscript. This study was supported by the University of Chicago Materials Research Science and Engineering Center and The Department of Energy (DP).
Author information
Authors and Affiliations
Corresponding author
Additional information
Communicated by Hugh Dickinson.
Rights and permissions
About this article
Cite this article
Updegraff, E.P., Zhao, F. & Preuss, D. The extracellular lipase EXL4 is required for efficient hydration of Arabidopsis pollen. Sex Plant Reprod 22, 197–204 (2009). https://doi.org/10.1007/s00497-009-0104-5
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00497-009-0104-5