Comparative Analysis of the Arabidopsis Pollen Transcriptome  

Abstract

We present a genome-wide view of the male gametophytic transcriptome in Arabidopsis based on microarray analysis. In comparison with the transcriptome of the sporophyte throughout development, the pollen transcriptome showed reduced complexity and a unique composition. We identified 992 pollen-expressed mRNAs, nearly 40% of which were detected specifically in pollen. Analysis of the functional composition of the pollen transcriptome revealed the over-representation of mRNAs encoding proteins involved in cell wall metabolism, cytoskeleton, and signaling and under-representation of mRNAs involved in transcription and protein synthesis. For several gene families, we observed a common pattern of mutually exclusive gene expression between pollen and sporophytic tissues for different gene family members. Our results provide a 50-fold increase in the knowledge of genes expressed in Arabidopsis pollen. Moreover, we also detail the extensive overlap (61%) of the pollen transcriptome with that of the sporophyte, which provides ample potential to influence sporophytic fitness through gametophytic selection.

A reference map of the Arabidopsis thaliana mature pollen proteome

“…Interestingly, the majority of these proteins (75%) are preferentially implicated in the determination of protein fate rather than in protein synthesis. This is consistent with the idea that Arabidopsis mature pollen is charged with a pre-formed translational apparatus enabling rapid activation upon hydration and germination [10]. A considerable number (27%, i.e., 33 proteins) of the experimentally identified polypeptides are of unknown function.…”

“…Presence of proteins identified in our study was compared to data obtained by a previous transcriptome analysis of mature pollen [10]. In terms of functional categories, general metabolism (20.6%), protein processing (9%), and stress-related (4%) functions assigned on the basis of our proteomic approach reflect similar proportions, namely 18%, 6%, and 6%, respectively, in the microarraybased transcriptome study.…”

“…Alternatively, since metabolic enzymes are generally highly abundant, soluble proteins, this functional category might be overrepresented in our analysis. The latter hypothesis appears more likely since only $19% of the pollen transcriptome encodes metabolic proteins (see below; [10]). In detail, $19% of the identified proteins implicated in metabolic functions are related to carbohydrate metabolism (e.g., triosephosphate isomerase -At3g55440-, glycoside hydrolase -At3g5440-, glucose dehydrogenase -At5g15490-, or fructose-bisphospate aldolase -At3g52930) and $51% to energy metabolism.…”

“…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.…”

“…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.…”