The Rab Geranylgeranyl Transferase Beta Subunit Is Essential for Embryo and Seed Development in Arabidopsis thaliana.

Joanna Rojek,Michał Rychłowski,Julita Nowakowska,Matthew R Tucker,Małgorzata Gutkowska

doi:10.3390/ijms22157907

Abstract

Auxin is a key regulator of plant development affecting the formation and maturation of reproductive structures. The apoplastic route of auxin transport engages influx and efflux facilitators from the PIN, AUX and ABCB families. The polar localization of these proteins and constant recycling from the plasma membrane to endosomes is dependent on Rab-mediated vesicular traffic. Rab proteins are anchored to membranes via posttranslational addition of two geranylgeranyl moieties by the Rab Geranylgeranyl Transferase enzyme (RGT), which consists of RGTA, RGTB and REP subunits. Here, we present data showing that seed development in the rgtb1 mutant, with decreased vesicular transport capacity, is disturbed. Both pre- and post-fertilization events are affected, leading to a decrease in seed yield. Pollen tube recognition at the stigma and its guidance to the micropyle is compromised and the seed coat forms incorrectly. Excess auxin in the sporophytic tissues of the ovule in the rgtb1 plants leads to an increased tendency of autonomous endosperm formation in unfertilized ovules and influences embryo development in a maternal sporophytic manner. The results show the importance of vesicular traffic for sexual reproduction in flowering plants, and highlight RGTB1 as a key component of sporophytic-filial signaling.

Highlights

Flowering plants, which dominate present-day flora, have developed a sophisticated and successful system of propagation by seeds
To our surprise we found that more than 10% of the RGTB1/rgtb1 embryos developing on the rgtb1/rgtb1 plants pollinated with WT were larger than their WT counterparts
PIN1 is the main auxin transporter involved in auxin localization in the apical half of the Arabidopsis embryo [58]; we studied its distribution (Figure 8)

Summary

Introduction

Flowering plants, which dominate present-day flora, have developed a sophisticated and successful system of propagation by seeds. The angiosperm female gametophyte (FG) undergoes double fertilization. The haploid egg cell is fertilized by one sperm cell to form a zygote [1]. Mitotic divisions of the zygote follow and give rise to the embryo, which by the 16-cell globular stage exhibits differentiated inner and outer cell layers. In Arabidopsis, when the embryo contains 32 cells, it undergoes a transition from globular to bilateral symmetry, initiating cotyledons (embryonic leaves) and a radicle (embryonic root). The endosperm arises from the diploid central cell, which is fertilized by the second sperm cell [1]. The initial divisions of the triploid nuclei in the endosperm are not followed by a cytokinesis and the endosperm, develops as a syncytium; only when the embryo has reached early heart stage does the endosperm cellularize [2]

Methods

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Discussion

Conclusion