The extracellular lipase EXL4 is required for efficient hydration of Arabidopsis pollen |
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Authors: | Emily P Updegraff Fang Zhao Daphne Preuss |
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Institution: | (1) Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637, USA |
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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. |
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Keywords: | Pollen Hydration Extracellular lipase EXL4 GRP17 |
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