Proteomic analyses ofOryza sativa mature pollen reveal novel proteins associated with pollen germination and tube growth

Abstract

As a highly reduced organism, pollen performs specialized functions to generate and carry sperm into the ovule by its polarily growing pollen tube. Yet the molecular genetic basis of these functions is poorly understood. Here, we identified 322 unique proteins, most of which were not reported previously to be in pollen, from mature pollen of Oryza sativa L. ssp japonica using a proteomic approach, 23% of them having more than one isoform. Functional classification reveals that an overrepresentation of the proteins was related to signal transduction (10%), wall remodeling and metabolism (11%), and protein synthesis, assembly and degradation (14%), as well as carbohydrate and energy metabolism (25%). Further, 11% of the identified proteins are functionally unknown and do not contain any conserved domain associated with known activities. These analyses also identified 5 novel proteins by de novo sequencing and revealed several important proteins, mainly involved in signal transduction (such as protein kinases, receptor kinase-interacting proteins, guanosine 5'-diphosphate dissociation inhibitors, C2 domain-containing proteins, cyclophilins), protein synthesis, assembly and degradation (such as prohibitin, mitochondrial processing peptidase, putative UFD1, AAA+ ATPase), and wall remodeling and metabolism (such as reversibly glycosylated polypeptides, cellulose synthase-like OsCsLF7). The study is the first close investigation, to our knowledge, of protein complement in mature pollen, and presents useful molecular information at the protein level to further understand the mechanisms underlying pollen germination and tube growth.

Proteomics Identification of Differentially Expressed Proteins Associated with Pollen Germination and Tube Growth Reveals Characteristics of Germinated Oryza sativa Pollen

“…2). ␤-1,4-Xylanase, a main pollen coat protein of maize (20) and rice (14), which is deposited into the pollen coat from tapetal cells of anthers (20) and whose transcripts are absent in MPGs and GPGs (Fig. 3), was present at a high level in MPGs but barely detectable in GPGs (Fig.…”

“…But numerous studies have revealed that some or all proteins in the pollen coat, a specialized layer outside the wall, and several pollen wall-associated species, either from pollen itself or from sporophytic tissues of anthers, are releasable during pollen germination (14,20); and after pollination and germination on the stigma, the germinating pollen will release some interior proteins for interaction with the stigma to facilitate tube growth in pistils. Thus, the RVreduced proteins or those that have disappeared in the germinated pollen may result from real down-regulated expression and/or release of coat/wall-associated and pollen-interior proteins into the germination medium.…”

“…Recent proteomics studies from Arabidopsis (12,13) and rice (14) have revealed that mature pollen presynthesizes a complement of proteins required for pollen function, including those implicated in protein synthesis and carbohydrate/energy metabolism. Dai et al (14) showed that these functional categories related to carbohydrate/energy metabolism, wall metabolism, protein synthesis and degradation, and signaling are overrepresented in the proteome.…”

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

“…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).…”

Combined Proteomic and Cytological Analysis of Ca2+-Calmodulin Regulation inPicea meyeriPollen Tube Growth

“…Studies focusing solely on the proteome of the male gametophyte have been performed in Arabidopsis and Pinus strobus (Fernando, 2005;Holmes-Davis et al, 2005). Recent proteomic investigations of pollens from Arabidopsis, rice, and gymnosperms have provided opportunities to complement the information derived from transcriptomic analysis and offered new insights into the mechanisms underlying pollen functional specification (Noir et al, 2005;Dai et al, 2006Dai et al, , 2007Sheoran et al, 2006). However, pollen tube development in conifers (gymnosperm) differs in several ways from that in angiosperms, such as in the extended growth period, relatively slow growth rate, and extremely delayed gametogenesis, which represent a major evolutionary divergence in male gametophyte development in the flowering plants (Fernando, 2005Williams, 2008).…”