PIN-formed protein, a door to reveal the mechanism for auxin-triggered initiation of cotton fiber

Abstract

Cotton fibers are differentiated ovule epidermal cells that provide an ideal model to study cell differentiation and elongation. Establishment of auxin maximum in fiber cells is crucial for cotton-fiber protrusion from ovule surface. However, it is unclear where the auxin originates from and how the auxin accumulates in fiber cells. Our recent results indicate that the auxin is mainly imported from the outside of ovules, and transported to fiber cells through GhPIN (homolog of PIN-formed proteins in cotton) -mediated polar auxin transport, rather than in situ synthesis. Based on our finding in GhPINs, we discuss here briefly how auxin flow to fiber cells and auxin gradient in ovule epidermis is established mainly by GhPIN3a protein.

Keywords: Auxin; GhPIN3; cotton fibers; ovules; polar localization.

Figure 1.

Possible model for GhPIN3a-mediated auxin accumulation in cotton fibers. (A) Auxin distribution in 0-DPA ovules. (B) Expression of GhPIN3a in 0-DPA ovules. (C) Speculative auxin routes to the ovule nucellus and outer integument. (D) Possible localization of GhPIN3a in ovule epidermal and sub-epidermal layers. F, fiber cells; NF, non-fiber cells; OI, ovule outer integument; II, ovule inner integument; N, ovule nucellus.