Penetration of the Stigma and Style Elicits a Novel Transcriptome in Pollen Tubes, Pointing to Genes Critical for Growth in a Pistil

Abstract

Pollen tubes extend through pistil tissues and are guided to ovules where they release sperm for fertilization. Although pollen tubes can germinate and elongate in a synthetic medium, their trajectory is random and their growth rates are slower compared to growth in pistil tissues. Furthermore, interaction with the pistil renders pollen tubes competent to respond to guidance cues secreted by specialized cells within the ovule. The molecular basis for this potentiation of the pollen tube by the pistil remains uncharacterized. Using microarray analysis in Arabidopsis, we show that pollen tubes that have grown through stigma and style tissues of a pistil have a distinct gene expression profile and express a substantially larger fraction of the Arabidopsis genome than pollen grains or pollen tubes grown in vitro. Genes involved in signal transduction, transcription, and pollen tube growth are overrepresented in the subset of the Arabidopsis genome that is enriched in pistil-interacted pollen tubes, suggesting the possibility of a regulatory network that orchestrates gene expression as pollen tubes migrate through the pistil. Reverse genetic analysis of genes induced during pollen tube growth identified seven that had not previously been implicated in pollen tube growth. Two genes are required for pollen tube navigation through the pistil, and five genes are required for optimal pollen tube elongation in vitro. Our studies form the foundation for functional genomic analysis of the interactions between the pollen tube and the pistil, which is an excellent system for elucidation of novel modes of cell–cell interaction.

Two Arabidopsis Loci Encode Novel Eukaryotic Initiation Factor 4E Isoforms That Are Functionally Distinct from the Conserved Plant Eukaryotic Initiation Factor 4E

“…EIF4E1B was identified as a gene up-regulated during pollen tube growth (Wang et al, 2008). Additionally, EIF4E1B was significantly enriched in pollen tubes grown by a semi in vivo method (Qin et al, 2009). EIF4E1B was identified as a sperm-enriched gene, while EIF4E was sperm depleted (Borges et al, 2008).…”

Dynamic Adaption of Metabolic Pathways during Germination and Growth of Lily Pollen Tubes after Inhibition of the Electron Transport Chain

“…So far, the majority of transcriptome studies did not consider time-dependent aspects during germination and tube growth but were focused on the differences between pollen and sporophytic tissue or emphasized specific biological processes in pollen physiology and development or described differences between pollen grains and tubes of various species (Becker et al, 2003;Honys and Twell, 2003;Bock et al, 2006;Haerizadeh et al, 2009;Qin et al, 2009;Hafidh et al, 2012). A metabolic network was presented for Arabidopsis pollen using the transcriptome data of Pina et al (2005) and the MAPMAN software (Thimm et al, 2004).…”

“…The majority of studies including proteomic studies focused on differences between the expression levels of pollen and sporophytic tissue or of different states in pollen development (Becker et al, 2003;Honys and Twell, 2003;Pina et al, 2005;Bock et al, 2006). Only few studies focused on pollen tube growth (Dai et al, 2006;Wang et al, 2008;Grobei et al, 2009;Qin et al, 2009). Although metabolic pathway networks were reconstructed from these data (Boavida et al, 2005;Colaço et al, 2012) using the MAPMAN tool (Thimm et al, 2004), the correlation between the presence of mRNA, the amount of protein, and its specific activity remains uncertain (Gry et al, 2009;Taniguchi et al, 2010).…”

Whole Genome Analysis of Gene Expression Reveals Coordinated Activation of Signaling and Metabolic Pathways during Pollen-Pistil Interactions in Arabidopsis

“…A primary transcriptomic comparison of UP, ovules, and siliques enriched the UP and ovule data sets for stage-specific transcripts by excluding common sporophyte-expressed genes potentially involved in carpel and ovule determination, such as SEEDSTICK (STK; Rounsley et al, 1995) and SHATTERPROOF1 (SHP1; Flanagan et al, 1996), a phosphogluconolactonase (At5g24420) that is expressed in ovule integuments and in the ovary wall (Scutt et al, 2003), as well as genes involved in later stages of seed development, such as MEDEA (MEA; Vielle-Calzada et al, 1999), FERTILIZATION INDE-PENDENT SEED2 (Luo et al, 1999), and FLOWERING WAGENINGEN (Kinoshita et al, 2004). Using the parameters outlined in "Materials and Methods" and further comparison with publicly available data sets (Zimmermann et al, 2004;Tung et al, 2005;Yu et al, 2005;Steffen et al, 2007;Borges et al, 2008;Wang et al, 2008;Qin et al, 2009;Wuest et al, 2010), a total of 42 genes were considered enriched or preferentially expressed in ovules (Supplemental File S1). As anticipated, 27 out of 42 transcripts preferentially expressed in ovules and 96 out of 1,275 ovule-enriched transcripts were previously reported to be expressed specifically in the embryo sac or enriched in female gametophytic cells (Supplemental File S1; Yu et al, 2005;Johnston et al, 2007;Punwani et al, 2007;Steffen et al, 2007;Wuest et al, 2010).…”

“…More notably, recent progress in the isolation of Arabidopsis (Arabidopsis thaliana) gametes allowed genomewide expression profiling of purified sperm cells (Borges et al, 2008) as well as of isolated egg and central cells (Wuest et al, 2010). In addition, the transcriptomes of in vitro pollen tube growth (Wang et al, 2008) and of pollen tubes growing in a semi-in vitro system (Qin et al, 2009) unfolded a new level of complexity of gene regulation occurring during the reproductive process. However, the analysis of individual partners or particular cellular processes cannot provide a complete outline of the molecular events acting during plant reproduction, in that they do not fully represent the way that individual elements relate with each other in vivo in a precise timing and developmental context.…”