| In plants, the actin cytoskeleton plays a basic role in cellular transport, cellgrowth, cell polarized and morphology formation. And formins play a centralregulator in actin polymerization and some physical activities based on actin filament.We focused on OsFH1which belongs to rice Formins to study the biological functionin vitro or invivo.In the actin binding proteins reported in recent years, Formin family attractsmore attention. In plants, Formins are divided into two categories, type I and type IIbased on sequence homology of their FH2domains. Type I Formins account for alarge proportion in the current report. OsFH1is a typical type I Formin containing SP,TM, FH1, FH2domains. The FH1domain contains a typical polyproline-rich regionimplicated in binding to profilin or actin/profilin complex. The FH2domain alsocontains the key sequence that is highly conserved among type I formins. To clarifyits biological functions, we chose pollen tube as a model organism in the nicotiana.Overexpression of OsFH1arrest pollen tube growth and caused pollen tube swelling.We stained the pollen tube with alexa Fluor568phalloidin, overexpression of OsFH1induces the Formation of excessive actin cables in the pollen tubes and causes swollenpollen tubes to swell. To test the chemical properties of OsFH1, the FH1-FH2domain (amino acid352to903) and FH2domain (amino acid505to903)recombinant proteins were selected. We purified both FH1FH2and FH2fusionproteins with a6-His tag at N terminus in Escherichia coli. By using pyrene labbledactin assay and TIRFM, it is found that OsFH1-FH2and OsFH1-FH1FH2both canbind to the actin filaments, polymerize the G-actin to F-actin and bind to the barbedend to cap it. OsFH1-FH1FH2can buddle the actin, but OsFH1-FH2does not havethe similar activity. These results show OsFH1can modulate the pollen tube growthvia interact with microfilaments. It is helpful for us to understand the formation of thecytoskeleton and the polar growth of the plant pollen tubes. |
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