Sporophytic control of pollen tube growth and guidance in grasses

Abstract

Pollen tube growth and guidance in the female tissues of flowering plants is a long-studied and anatomically well-described process. A large number of gene products and chemical compounds involved have been identified in the last 20 years, and some underlying molecular mechanisms including self-incompatibility in the Brassicaceae, Solanaceae and Papaveraceae are now well understood. However, the largest part of the pollen tube pathway inside the transmitting tract towards the ovule harbouring the female gametophyte still requires intensive investigations. Especially in the economically most import plant family, the Poaceae or grasses, progamic pollen tube development is barely understood. Using maize as a model, we propose to divide pollen tube germination, growth and guidance towards the female gametophyte into five distinct phases. The model is adapted from Arabidopsis thaliana, taking anatomical differences and novel genetic and cellular studies into consideration. With the exception of Phase V, all phases seem to be under sporophytic control in grasses.

Female gametophyte-controlled pollen tube guidance

“…200 μm in T. fournieri [6], whereas approx. 100 μm has been observed in Arabidopsis and maize [7,15,18,21]. Laser-assisted cell ablation experiments with Torenia ovules containing naked FGs have shown further that the synergid cells are necessary and sufficient to attract PTs and that neither the egg cell nor the central cell seems to be involved in this process and are capable of generating sufficient amounts of guidance molecule(s).…”

“…The last path of PT attraction controlled by the FG was therefore divided into at least two steps: (i) guidance from the surface of the placenta to the funiculus (funicular guidance), and (ii) guidance from the entrance of the micropyle to the FG or embryo sac (micropylar guidance) [6,11,12]. Since a funiculus is lacking in grasses (Poaceae), gametophytic PT attraction involves only the latter phase [7].…”

“…Excellent recent reviews offering updates in the mechanic and molecular processes of PT germination and sporophytic guidance have been published elsewhere [6][7][8][9] and we therefore restrict the present review to PT guidance governed by the FG.…”

Natural variation in PTB1 regulates rice seed setting rate by controlling pollen tube growth

“…Our data therefore reveal a key factor for PT growth and an important regulator of rice PSSR. Although abnormalities of PTs within the rice pistil result in a spectrum of growth phenotypes depending on the PTB1 expression level, none are observed to exhibit the classic defects in PT micropyle guidance 16,41 (Figs 2 and 6b,d) that are generally believed to be controlled by cues emitted from the female gametophyte [19][20][21] . This finding is consistent with the result that the mature embryo sac of the mutant is morphologically normal (Supplementary Fig.…”

Control of Programmed Cell Death During Plant Reproductive Development

“…Multiple signaling events have to occur successfully after pollination before the pollen tube can finally join the female gametophyte (Lausser and Dresselhaus 2010;Marton and Dresselhaus 2010;Okuda and Higashiyama 2010). Double fertilization results in two individual fertilization products: the diploid zygote that will develop into the embryo and the triploid nutritive tissue of the endosperm.…”