A glycine-rich protein that facilitates exine formation during tomato pollen development

Abstract

Formation of the unique and highly diverse outer cell wall, or exine, of pollen is essential for normal pollen function and survival. However, little is known about the many contributing proteins and processes involved in the formation of this wall. The tomato gene LeGRP92 encodes for a glycine-rich protein produced specifically in the tapetum. LeGRP92 is found as four major forms that accumulate differentially in protein extracts from stamens at different developmental stages. The three largest molecular weight forms accumulated during early microspore development, while the smallest molecular weight form of LeGRP92 was present in protein extracts from stamens from early microsporogenesis through anther dehiscence, and was the only form present in dehisced pollen. Light microscopy immunolocalization experiments detected LeGRP92 at only two stages, late tetrad and early free microspore. However, we observed accumulation of the LeGRP92 at the early tetrad stage of development by removing the callose wall from tetrads, which allowed LeGRP92 detection. Transmission electron microscopy confirmed the LeGRP92 accumulation from microspore mother cells, tetrads through anther dehiscence. It was observed in the callose surrounding the microspore mother cells and tetrads, the exine of microspores and mature pollen, and orbicules. Plants expressing antisense RNA had reduced levels of LeGRP92 mRNA and protein, which correlated to pollen with altered exine formation and reduced pollen viability and germination. These data suggest that the LeGRP92 has a role in facilitating sporopollenin deposition and uniform exine formation and pollen viability.

Integrated analysis of transcriptome and proteome changes related to the Ogura cytoplasmic male sterility in cabbage

“…The characteristics of LTPs make them candidates for translocation of the sporopollenin precursors from tapetum to microspores in Brassicaceae [ 47 ]. In the tapetum, antisense down-regulation of tomato GRP92 , a homologous gene of LTPs, resulted in an abnormal exine [ 71 ]. Three LTP12 DEGs were expressed at very low levels in R2P2CMS compared to R2P2, and were in the cell wall responsible for establishment of localization by GO Process.…”

Pollen-Expressed Leucine-Rich Repeat Extensins Are Essential for Pollen Germination and Growth

“…Mutations in Arabidopsis AGP6 and AGP11 and in Brassica campestris male fer-tility8 were shown to cause reduced pollen germination rates and impaired pollen tube growth (Levitin et al, 2008;Coimbra et al, 2009Coimbra et al, , 2010. Similarly, in tomato, the Gly-rich protein LeGRP92 has been implicated in pollen exine development, pollen viability, and poor germination (McNeil and Smith, 2010). Thus, cell wall proteins play important roles in maintaining the integrity of pollen tubes.…”

Tomato Male sterile 1035 is essential for pollen development and meiosis in anthers

“…For example, Solyc03g116930.2.1 is homologous to yeast PRECOCIOUS DISSOCIATION OF SISTERS PROTEIN5 ( PDS5 ), which is important for sister chromatid cohesion such as chromosome condensation, pairing, and synapsis in prophase I ( Jin et al , 2009 ). Solyc02g032910.1.1 is predicted to encode a protein highly similar to glycine-rich protein, which is important for sporopollenin deposition on meiocyte and exine formation ( McNeil and Smith, 2010 ). Another downregulated gene, Solyc06g076020.2.1 , is similar to Heat shock protein 70 ( Hsp70 ), which has an important role supporting cyclin-dependent kinase activity in meiosis I in animals ( Eddy, 1999 ).…”