Transcriptional Profiling of Arabidopsis Tissues Reveals the Unique Characteristics of the Pollen Transcriptome

Abstract

Pollen tubes are a good model for the study of cell growth and morphogenesis because of their extreme elongation without cell division. Yet, knowledge about the genetic basis of pollen germination and tube growth is still lagging behind advances in pollen physiology and biochemistry. In an effort to reduce this gap, we have developed a new method to obtain highly purified, hydrated pollen grains of Arabidopsis through flowcytometric sorting, and we used GeneChips (Affymetrix, Santa Clara, CA; representing approximately 8,200 genes) to compare the transcriptional profile of sorted pollen with those of four vegetative tissues (seedlings, leaves, roots, and siliques). We present a new graphical tool allowing genomic scale visualization of the unique transcriptional profile of pollen. The 1,584 genes expressed in pollen showed a 90% overlap with genes expressed in these vegetative tissues, whereas one-third of the genes constitutively expressed in the vegetative tissues were not expressed in pollen. Among the 469 genes enriched in pollen, 162 were selectively expressed, and most of these had not been associated previously with pollen. Their functional classification reveals several new candidate genes, mainly in the categories of signal transduction and cell wall biosynthesis and regulation. Thus, the results presented improve our knowledge of the molecular mechanisms underlying pollen germination and tube growth and provide new directions for deciphering their genetic basis. Because pollen expresses about one-third of the number of genes expressed on average in other organs, it may constitute an ideal system to study fundamental mechanisms of cell biology and, by omission, of cell division.Pollen has been the subject of intense studies not only for its importance as the male partner in plant reproduction, but also as a model for the study of cell growth and morphogenesis in a broader sense (Feijó et al., 2001). Whereas early studies focused on pollen physiology and biochemistry (for review, see Mascarenhas, 1975), the last 20 years have been marked by increasing efforts to decipher the genetic basis of pollen development and functions (for reviews, see Scott et al., 1991;McCormick, 1993;Preuss, 1995;Taylor and Hepler, 1997; Franklin-Tong, 1999; Hepler et al., 2001;Lord and Russell, 2002). These efforts led to the identification of more than 150 pollenexpressed genes from more than 28 species (Twell, 2002). These genes encode proteins thought or known to be involved in pollen development, pollen germination, and pollen tube growth, as well as in interactions with the stigma/transmitting tissue or the female gametophyte. Many of these studies were conducted in Lilium sp. or in Solanaceae species, because their pollen is easily collected in sufficient quantities, and methods for in vitro germination are robust. However, the available genetic information for these species is limited. The availability of the genome sequence of Arabidopsis (The Arabidopsis Genome Initiative, 2000) and the concomitant increase in availab...

AtTIP1;3 and AtTIP5;1, the only highly expressed Arabidopsis pollen‐specific aquaporins, transport water and urea

“…In order to characterize the aquaporin genes that are expressed in mature pollen, we used information available from different transcriptional profilings of A. thaliana mature pollen [4][5][6][7][8][9]. We selected all aquaporin homologs that were selectively expressed in pollen and also ranked within the top 50% of pollen-expressed genes (according to [7]).…”

“…Interestingly, they both belonged to the TIP subfamily: AtTIP5;1 (GeneID: 823898, locus tag: At3g47440) and AtTIP1;3 (GeneID: 828051, locus tag: At4g01470). AtTIP5;1 and AtTIP1;3 are also both ranked within the top 10% of Arabidopsis mature pollen-expressed genes [4][5][6][7][8][9]. Microarray data available at GENEVESTIGA-TOR (http://www.genevestigator.ethz.ch) showed for At-TIP5;1 and AtTIP1;3 the highest expression level in mature pollen, moderate in flower, very low in inflorescence and non-detectable in any other plant tissue (Fig.…”

“…In particular the Arabidopsis thaliana genome has been an important source of information for the study of gene expression patterns in pollen through the use of commercial oligonucleotide microarrays [4][5][6][7][8][9]. Even though the Arabidopsis genome contains 35 loci for aquaporins, functional analyses of many of them are still missing.…”

A reference map of the Arabidopsis thaliana mature pollen proteome

“…The availability of the full genome sequence of Arabidopsis [8] has made genome-wide, microarray-based analyses of the male gametophyte transcriptome of this model plant possible [9][10][11][12]. 13,977 male gametophyte-expressed mRNAs were recently identified using the ATH1 Genome Array, which covers $81% of the currently estimated 28,000 protein-coding genes in Arabidopsis.…”

“…In the model plant Arabidopsis thaliana, the extremely reduced, tricellular male gametophyte constitutes an ideal experimental system for analyses of important biological processes in higher plant reproduction. In addition, it represents a very useful model for studying fundamental aspects of plant biology such as cell fate determination, cell-cell interactions, cell polarity, and tip-growth [5][6][7].The availability of the full genome sequence of Arabidopsis [8] has made genome-wide, microarray-based analyses of the male gametophyte transcriptome of this model plant possible [9][10][11][12]. 13,977 male gametophyte-expressed mRNAs were recently identified using the ATH1 Genome Array, which covers $81% of the currently estimated 28,000 protein-coding genes in Arabidopsis.…”