Auxin polar transport in stamen formation and development: how many actors?

Abstract

In flowering plants, proper development of stamens, the male reproductive organs, is required for successful sexual reproduction. In Arabidopsis thaliana normally six stamen primordia arise in the third whorl of floral organs and subsequently differentiate into stamen filaments and anthers, where male meiosis occurs, thus ending the early developmental phase. This early phase is followed by a late developmental phase, which consists of a rapid elongation of stamen filaments coordinated with anther dehiscence and pollen maturation, and terminates with mature pollen grain release at anthesis. Increasing evidence suggests that auxin transport is necessary for both early and late phases of stamen development. It has been shown that different members of PIN (PIN-FORMED) family are involved in the early phase, whereas members of both PIN and P-glycoproteins of the ABCB (PGP) transporter families are required during the late developmental phase. In this review we provide an overview of the increasing knowledge on auxin transporters involved in Arabidopsis stamen formation and development and we discuss their role and functional conservation across plant species.

Keywords: Arabidopsis; auxin transport; dicots; monocots; stamen development.

Figure 1

The Arabidopsis stamen. (A) A mature flower at anthesis showing short and long stamens (with the removal of some petals and sepals for visualization). (B) Cartoon of a stamen at a stage after meiosis (left) and of the stamen transverse section, at the level of the anther, with differentiated tissues indicated in different colors (right). Based on Sanders et al. (2000), Jia et al. (2008), Smyth (2010). (C) A diagram showing different floral organs with stamens depicted in pink. Based on Bowman (1994), Whipple et al. (2004). (D) Schematic representation of early development of stamens in Arabidopsis flowers at floral stages from 5 to 9/anther stages from 1 to 5. Stamens are depicted in pink. Based on Ito et al. (2007), Alvarez-Buylla et al. (2010).

Figure 2

Late development of stamens in flower buds from stages 10 to 13. Main events in the development of anther, pollen, and filament occurring in stamens during late flower development.

Figure 3

Auxin transport in stamens during early and late developmental stages. (A,B) Stamen primordia (yellow) at stage 5 (A) and 6 (B) of flower development. Places of auxin accumulation are depicted in purple. Presumptive routes of auxin transport are depicted by black arrows. (C) A stamen at stage 11 of flower development (left). Cartoon of a longitudinal section of a stamen at stage 11 of flower development (right). Basipetal auxin transport in the stamen filament is depicted by black arrows in epidermal cells and vascular tissue. Arrowheads indicate regulation of auxin homeostasis inside pollen grains. E, epidermal cells; L1, L1 layer; PG, pollen grains; V, vascular tissue.