Proteomic evaluation of gymnosperm pollination drop proteins indicates highly conserved and complex biological functions

Abstract

The pollination droplet is a highly conservative pollination mechanism that is observed in all major gymnosperm taxa. Proteomics analysis of the pollination drops was carried out on four gymnosperm species: Juniperus communis (common juniper), Juniperus oxycedrus (prickly juniper), Chamaecyparis lawsoniana (Port Orford cedar), and Welwitschia mirabilis. Pollination drop proteins were purified by SDS-PAGE, and the most abundant proteins were analyzed by mass spectrometry and sequenced. Based on BLAST searching of combined amino acid sequences, the following proteins were identified in the following species: an 83-kDa subtilisin-like proteinase, a 62-kDa glycosyl hydrolase, a 47.5-kDa glucan 1,3-b-glucosidase precursor, a 30-kDa chitinase, and a 25-kDa thaumatin-like protein were identified in J. communis; a 30-kDa chitinase, a 25-kDa thaumatin-like protein, and a 32.5-kDa glucanase-like protein were identified in J. oxycedrus; an 83-kDa subtilisin-like proteinase, a 62-kDa b-D-glucan exohydrolase, a 47.5-kDa glucan 1,3-b-glucosidase, and two 25-kDa thaumatin-like proteins were identified in C. lawsoniana, and a 25-kDa chitinase was identified in W. mirabilis. Based on protein identifications, there is strong evidence that the pollination drop functions in both pathogen defense and pollen development. The discovery of similarities in terms of peptide sequence and protein identifications indicates that ovular secretions are functionally conservative, and that they are essential to reproductive success.

The Pollination of Mid Mesozoic Seed Plants and the Early History of Long-proboscid Insects1,2,3

“…Fern nectaries produce watery, nutritionally poor secretions, whereas carbohydrate and amino acid concentrations of pollen drops from the four major lineages of gymnosperms-conifers, Ginkgo L., cycads, and gnetaleans-showed significantly more elevated nutritional levels, particularly in the two latter insectpollinated clades (Labandeira et al, 2007a). Nutritional levels in pollination drops of the four gymnosperm clades are similar to those of nectar from basal angiosperm lineages (Labandeira et al, 2007a;Wagner et al, 2007;Nepi et al, 2009). Lipid levels were not measured.…”

Amino acids and protein profile in floral nectar: Much more than a simple reward

“…Extrafloral nectar also has its own enzymatic defense against invasion by micro-organisms, the predominant enzymes being chitinase, ␤-1,3-glucanase and thaumatine-like proteins . Defense proteins such as glucosidases, chitinases, hydrolases, and thaumatine-like proteins have also been detected in pollination drops (Wagner et al, 2007), secretions produced by the ovules of gymnosperms and that possess a chemical composition similar to that of angiosperm nectar (Nepi et al, 2009).…”

Identification and cloning of class II and III chitinases from alkaline floral nectar of Rhododendron irroratum, Ericaceae

“…Experimental evidence for chitinases acting as defense proteins has been obtained using transgenic plants that overexpressed chitinases and exhibited higher resistance to pathogens (Schlumbaum et al 1986;Broglie et al 1991;Minic 2008). Wagner et al (2007) firstly detected chitinase (class IV, GH19 family) in pollination drop of several gymnosperm species, Juniperus communis, Juniperus oxycedrus and Welwitschia mirabilis. Gonzalez-Teuber et al (2010) identified class I chitinase (GH19) in extrafloral nectar of Acacia species, and Escalante- Perez et al (2012) identified classes III (GH18), IV (GH19), and V (GH18) in extrafloral nectar of Populus trichocarpa.…”