In search of ligands and receptors of the pollen tube: the missing link in pollen tube perception

Abstract

The journey undertaken by the pollen tube in angiosperms to reach the deeply embedded female gametophyte for fertilization involves persistent guidance by the female gametophyte and accurate perception of the signals by the pollen tube. Several ovule-secreted peptides have been identified. Nevertheless, there are no exact findings on how these signals are perceived by the pollen tube. As a novel approach, we have improvised a modified SIV (semi-in vivo) technique, SIV-PS (SIV pollen tube secretome), to perform gel-free LC-MS/MS for high-throughput analysis of pollen-tube-secreted proteins. Our approach has led to the identification of over 1400 protein groups. Among them are pollen-tube-secreted ligands and receptor proteins representing potential male components in perceiving ovule-emitted cues for guidance. The present article reviews the missing link in pollen tube perception and showcases the improvised SIV-PS as a tool for high-throughput and targeted study of the pollen tube secretome.

Quantitative proteomics of the tobacco pollen tube secretome identifies novel pollen tube guidance proteins important for fertilization

“…Previously, we optimized a technique for tobacco pollen tube growth through the female stylar explant to detect pollen tube-secreted proteins following penetration through the female reproductive tissues. We termed this technique the semi-in vivo pollen tube-secretome (SIV-PS) assay [ 14 ]. In this study, we have coupled the SIV-PS assay with a gel-free and label-free semi-quantitative LC-MS/MS workflow to detect and quantify pollen tube-secreted proteins using minimum quantities of 2 μg of the pollen tube total secretome (Additional file 1 : Figure S1).…”

“…In vitro approaches are feasible but pollen tubes grown in vitro do not acquire the competence to respond to female guidance signals [ 16 ] and develop different pollen tube physiology [ 12 , 15 , 61 – 63 ]. In this study we have successfully demonstrated the application of a previously developed pollen tube semi-in vivo technique (SIV-PS) [ 14 ] combined with gel- and label-free quantitative LC-MS/MS as a powerful assay for the genome-wide characterization of pollen tube-secreted proteins following its penetration through stigma and style. The SIV-PS tool offers access to pistil-stimulated pollen tube-secreted proteins with minimal contamination.…”

“…Pistils with protruding pollen tubes were used for viability tests and microscopic analysis and the remaining pollen tubes were excised for RNA extraction. For a stepwise description, see [ 14 ]. A list of primers used for semi quantitative RT-PCR analysis is provided in Additional file 21 : Table S8.…”

“…The discovery of pollen tube-secreted proteins that perceive female-secreted signals has been hampered by the inaccessibility of the pollen tubes within pistils and the likelihood of contamination from surrounding female tissues. We have therefore improvised a semi-in vivo technique (SIV) for tobacco pollen tube growth through the pistil to allow capture and detection of proteins secreted by the pollen tube following its penetration through the stigma and style [ 14 ]. In contrast to in vitro grown pollen tubes, SIV pollen tubes have been shown to have unique transcriptomes [ 15 ] as well as the ability to respond to synthetic pollen tube attractant peptides (LUREs) secreted by female synergid cells of Torenia fournieri [ 3 , 16 ].…”

m5C Methylation Guides Systemic Transport of Messenger RNA over Graft Junctions in Plants

“…In Arabidopsis, TCTP1 is ubiquitously and relatively highly expressed and a lack of TCTP1 activity results in embryo abortion, lower number of secondary roots, and severely dwarfed plants with fewer cells [42,43]. TCTP1 protein, in line with a systemic function in other eukaryotes, has been detected in the Arabidopsis pollen tube secretome [44], and it was proposed that TCTP1 protein has a function in root development [42,45], suggesting that TCTP1 RNA transport to specific lateral root initiation sites (Figure 4) might be part of its signaling function. The function of the relatively lowly expressed Arabidopsis TCTP1 ortholog TCTP2 was not examined in Arabidopsis thaliana but in transgenic Nicotiana tabacum plants.…”