Preliminary Study On The Function Of AtFH7 And AtFH20 In Arabidopsis Primary Root Growth

There is an active cytoplasmic streaming in plant cells,accompanied by a highly dynamic of subcellular components.Studies have supported that the dynamic movements mainly depend on the continuous remodeling of the cytoskeleton,particularly microfilaments,which play an essential role in response to developmental and environmental signals.The formation and arrangement of actin filaments are regulated by a variety of actin-binding proteins.As one of the actin nucleation factors,Formin is widely present in eukaryotic cells.It has been found that Formin can regulate the nucleation and bundling of actin filaments,and some members can coordinate the synergistic effect of microfilaments and microtubules.Through the regulation of the backbone,Formin plays a key role in the process of cell growth and morphogenesis.In contrast to fungi and animals,Formin protein family in plant has evolved to form a unique protein structural domain composition,which mainly includes the FH1 and FH2 structural domains,but not the DIA,DAD,or GBD/FH3 that bind Rho GTPase.According to analysis of the highly conserved structural domain FH2,Formin protein family in plant is divided into two subfamily proteins,namely class Ⅰ Formin proteins and class Ⅱ Formin proteins.Due to the large number of Formin protein families in plants and the obvious functional redundancy,the research on Formin proteins in plant is still relatively limited.Based on the bioinformatic analysis of Formin proteins in Arabidopsis,the class Ⅰ Formin protein AtFH7 and class Ⅱ Formin protein AtFH20,which are highly expressed in root hairs and probably localized in the nucleus,are selected for preliminary functional investigation.and T-DNA insertion mutants of AtFH7 and AtFH20 were obtained and the atfh7 and atfh20 mutants with red fluorescence-labeled nuclei and green fluorescence-labeled microfilaments were obtained by hybridization.According to observations and statistical analyses of the root development,we mainly obtained the following results:1.After programmed cell death of root hair cells,the nucleus migrated back to the base of root hair and was degraded further.2.The root hairs of atfh7 became significantly denser and longer,and those of atfh20 became significantly thinner and shorter,but those of formin7-1/20-1 in which both AtFH7 and AtFH20 did not change significantly compared with control group,demonstrating that both AtFH7 and AtFH20 may have regulatory functions on the initiation and elongation processes of root hairs,and the two genes have opposite effects.AtFH7 has an inhibitory effect on root hair growth and AtFH20 has a promotive effect on root hair growth.3.The morphology and migration of nuclei in atfh7,atfh20 and formin7-1/20-1 root hairs were not significantly changed.AtFH7 and AtFH20,as actin-binding proteins,were not likely involved in the morphological regulation of nuclei and did not have decisive effect on the forward and backward migration of nuclei.4.Both root length and meristem zone are significantly longer in atfh7 mutants and shorter in atfh20 mutants,but in formin7-1/20-1 there is no significant difference in root length compared with control group,demonstrating that both AtFH7 and AtFH20 may have regulatory functions in cell division but with opposite effects.AtFH7 inhibited cell division and AtFH20 promoted cell division.In summary,both class Ⅰ Formin protein AtFH7 and class Ⅱ Formin protein AtFH20 have regulatory effects on cell division and polar growth.