Genetics/Genomics

Abstract

CS-22-4 - Hydroxyproline O-Arabinosylation in Pollen Tube Growth

Tuesday, July 17
9:33 AM - 9:53 AM

Sexual reproduction in flowering plants relies on the remarkably rapid elongation of pollen tubes to deliver sperm nuclei to receptive ovules triggering seed development. The pollen tube grows quickly and over considerable distances and must reorient its growth in response to several distinct guidance cues as it traverses the pistil tissue. These pollen tube abilities rely on its highly polarized and compositionally unique cell wall. This specialized cell wall is composed of various polysaccharides, including callose, pectins, as well as various glycoproteins. We have found that a specific type of glycoprotein modification is required for full pollen fertility: Hydroxyproline O-arabinosylation, the stepwise addition of short linear chains of arabinose sugars onto hydroxyproline residues. Pollen from Arabidopsis mutants of the enzymes that initiate or extend this sugar chain fail to fertilize ~90% of their available ovules leading to poor seed yield. The mutant pollen tubes show reduced total elongation in vitro, disrupted pollen tube morphology and meandering in vivo growth. Despite this strong effect on male fertility, female fertility and vegetative growth are normal, suggesting that the pollen tube is particularly sensitive to the loss of this modification although it is found broadly in plant cell walls. Both the modification itself and the hydroxyproline O-arabinosyltransferase enzymes that produce it are plant-specific, yet deeply conserved across all plants and green algae. Interestingly, we have found that in tomato, two of the four hydroxyproline O-arabinosyltransferases have been specifically devoted to modification of pollen proteins. They are expressed specifically in pollen, unlike their broadly expressed Arabidopsis counterparts, and are non-redundantly required for efficient male transmission, indicating a broadly conserved function for this modification in angiosperm reproduction.


 

Co-Authors

Steven Beuder – University of Michigan; Syeda Roop Fatima Jaffri – University of Michigan; Alexandria Dorchak – University of Michigan; Alyssa Clearwood – University of Michigan

Cora A. MacAlister, PhD

Assistant Professor
University of Michigan

Cora MacAlister is an Assistant Professor in the University of Michigan Department of Molecular, Cellular and Developmental Biology. The MacAlister lab studies sexual reproduction in flowering plants with particular emphasis on the role of glycoproteins (proteins modified by the addition of sugars). Plants produce a large and diverse group of secreted and cell wall-associated glycoproteins, the glycosylation of which can have profound impacts on protein structure and activity. Glycoproteins play important roles in both male and female reproductive tissues. The pollen tube is dependent on its specialized cell wall to quickly penetrate the pistil and redirect its growth to ultimately reach a receptive ovule. Meanwhile, the transmitting tissue of the pistil secretes a rich extracellular matrix that nutritionally and physically supports and guides pollen tube growth. The intimate interaction between pollen tube and pistil relies on these extracellular regions and their glycoproteins to ensure fertilization.

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