VANGUARD1 Encodes a Pectin Methylesterase That Enhances Pollen Tube Growth in the Arabidopsis Style and Transmitting Tract

Abstract

In flowering plants, penetration of the pollen tube through stigma, style, and transmitting tract is essential for delivery of sperm nuclei to the egg cells embedded deeply within female tissues. Despite its importance in plant reproduction, little is known about the underlying molecular mechanisms that regulate the navigation of the pollen tube through the stigma, style, and transmitting tract. Here, we report the identification and characterization of an Arabidopsis thaliana gene, VANGUARD1 (VGD1) that encodes a pectin methylesterase (PME)-homologous protein of 595 amino acids and is required for enhancing the growth of pollen tubes in the style and transmitting tract tissues. VGD1 was expressed specifically in pollen grain and the pollen tube. The VGD1 protein was distributed throughout the pollen grain and pollen tube, including the plasma membrane and cell wall. Functional interruption of VGD1 reduced PME activity in the pollen to 82% of the wild type and greatly retarded the growth of the pollen tube in the style and transmitting tract, resulting in a significant reduction of male fertility. In addition, the vgd1 pollen tubes were unstable and burst more frequently when germinated and grown on in vitro culture medium, compared with wild-type pollen tubes. Our study suggests that the VGD1 product is required for growth of the pollen tube, possibly via modifying the cell wall and enhancing the interaction of the pollen tube with the female style and transmitting tract tissues

Global analysis of gene expression in flower buds of Ms-cd1 Brassica oleracea conferring male sterility by using an Arabidopsis microarray

“…An ASK-beta gene (At3g61160) (Wellmer et al 2004) expressed in pollen and inside ovules was suppressed 3.9 fold. VGD1 (At2g47040), a pectin methylesterase gene, and 3 of it's homologues are expressed in the pollen grain and pollen tube (Jiang et al 2005 Plant Mol Biol (2008) 66:177-192 185 expressed before tetrad stage was detected being differentially expressed in the present study.…”

“…(Honys and Twell 2004) and stamen transcriptome (Wellmer et al 2004). PS, pollen specific; PS*, pollen specific gene confirmed by other reference (Jiang et al,2005);SP, stamen preferential; PP, pollen preferential; PE, pollen expressed; NDP, not detected in pollen previously c The data were concluded from pollen transcriptome dataset from reported pollen transcriptome (Honys and Twell 2004) …”

“…Notably, 13 genes including 4 genes classified as SP and 9 genes classified as NDP have expression levels of zero in the pollen transcriptome identified by Honys and Twell (2004). Except for AT2G47040 (VGD1), which was not detectable in Hony and Twell's experiment but was confirmed to be a pollen specific gene (Jiang et al 2005), the other 12 down regulated genes in Ms-cd1 flower buds including a reported tapetum specific gene MS2 (Aarts et al 1997) are most likely tapetum expressed or tapetum specific. To further clarify the association with fertility abortion in Ms-cd1, we compared expression patterns of these 12 genes with flower development expression data downloaded from Tair (http://www.arabidopsis.org) ( Table 3).…”

“…The gene MIA itself did not show an expression change in the Ms-cd1 mutant. A pectinase gene cluster Vanguard1 (VGD1) (Jiang et al 2005), AT2G47030, AT2G47040 and AT2G47050, which was down regulated in Ms-cd1, did not show differential expression in mia. AHA 9 (AT1G80660) which was significantly down regulated in Ms-cd1 was upregulated in mia.…”

Signaling Events in Pollen Acceptance or Rejection in the Arabidopsis Species

“…A specifi c example is the A. thaliana VANGUARD1 (VGD1) gene, which encodes a pectin methylesterase and is expressed in the pollen grain and pollen tube. VGD1 is required for pollen tube growth through the pistil as the vgd1 mutant displayed reduced levels of pectin methylesterase activity in the pollen grain and the pollen tube growth proceeded at a much slower rate compared to wild-type pollen (Jiang et al 2005 ). After a pollen tube grows through the stigmatic papillar cell wall to the base of the stigma, it enters into the transmitting tract, growing down to an ovule, where fertilization takes place (Lennon et al 1998 ;Cheung et al 2010 ).…”