The Functions of RHD6 and RSL4 in Root Hair Development along the Developmental zone of the Arabidopsis Root

Abstract

The gene regulatory networks are important molecular basis of the cell differentiation in multicellular organisms. Root hair development system in Arabidopsis is frequently used to analyze the gene regulatory network in plant. Especially, hair cell-specific genes govern the root hair morphogenetic processes such as hair initiation and elongation at the later stages of the root hair development (Grierson and Schiefelbein, 2002). RHD6 (ROOT HAIR DEFECTIVE 6, AT1G66470) and RSL4 (ROOT HAIR DEFECTIVE 6-LIKE 4, AT1G27740) are the hair cell-specific genes that encode the basic-helix-loop-helix (bHLH) transcription factors (Menand and Dolan, 2007, Yi and Dolan, 2010). RSL4 is direct target of RHD6. Both RHD6 and RSL4 are known to be expressed in the root meristem and elongation zone and regulate the root hair initiation and elongation. In this study, we investigated the importance of expression region of RHD6 and RSL4 and analyzed the inherent functions of RHD6 and RSL4 in the root hair formation. Our results showed the ectopic expression of RHD6 and RSL4 under various promoters, presents functions of RHD6 and RSL4 other than those known before. Auxin is the positive effector of root hair formation and modulates RSL4 expression via unknown mechanisms (Schiefelbein, 2000, Yi and Dolan, 2010). Our results suggested that RHD6 and auxin regulate the RSL4 expression in an independent manner and RHD6 has a target gene other than RSL4. We also found the possibility that RSL4 function has been conserved in angiosperms like RHD6 and EXPA7. These results extend our understanding of gene regulatory networks in the root hair development to angiosperm.