Functional Conservation of a Root Hair Cell-Specificcis-Element in Angiosperms with Different Root Hair Distribution Patterns

Abstract

Vascular plants develop distinctive root hair distribution patterns in the root epidermis, depending on the taxon. The three patterns, random (Type 1), asymmetrical cell division (Type 2), and positionally cued (Type 3), are controlled by different upstream fate-determining factors that mediate expression of root hair cell-specific genes for hair morphogenesis. Here, we address whether these root hair genes possess a common transcriptional regulatory module (cis-element) determining celltype specificity despite differences in the final root hair pattern. We identified Arabidopsis thaliana expansinA7 (At EXPA7) orthologous (and paralogous) genes from diverse angiosperm species with different hair distribution patterns. The promoters of these genes contain conserved root hair-specific cis-elements (RHEs) that were functionally verified in the Type-3 Arabidopsis root. The promoter of At EXPA7 (Type-3 pattern) also showed hair cell-specific expression in the Type 2 rice (Oryza sativa) root. Root hair-specific genes other than EXPAs also carry functionally homologous RHEs in their promoters. The RHE core consensus was established by a multiple alignment of functionally characterized RHEs from different species and by highresolution analysis of At EXPA7 RHE1. Our results suggest that this regulatory module of root hair-specific genes has been conserved across angiosperms despite the divergence of upstream fate-determining machinery.

Identical Amino Acid Substitutions in the Repression Domain of Auxin/Indole-3-Acetic Acid Proteins Have Contrasting Effects on Auxin Signaling

“…Of some 20 Aux/IAA proteins that have been tested to date, including 16 from Arabidopsis, all functioned as transcriptional repressors when expressed from effector plasmids in protoplast transfection assays (Ulmasov et al, 1997;Tiwari et al, 2001;Bargmann and Birnbaum, 2009). Consistent with the transfection results, targeted or constitutive expression of stabilized versions of IAA proteins in Arabidopsis plants resulted in suppression of auxin response genes and auxin-responsive growth and developmental responses (Fukaki et al, 2005;Kim et al, 2006;Nakamura et al, 2006;De Smet et al, 2007;Sato and Yamamoto, 2008;Ku et al, 2009;Li et al, 2009).…”

Root Hair-Specific EXPANSIN A7 Is Required for Root Hair Elongation in Arabidopsis

“…Moreover, expansin proteins localize at the root hair tip (Baluška et al, 2000) in Arabidopsis, and exogenous application of purified expansin proteins will cause the Arabidopsis root hair tip to burst . Previously, we identified two Arabidopsis expansin genes (AtEXPA7 and AtEX-PA18) that contain RHE consensus motifs in their promoter regions ( Cho and Cosgrove, 2002;Kim et al, 2006). Here, we demonstrated that the reduction of the levels of the AtEXPA7 transcript suppresses root hair elongation.…”

“…Next, the XhoI/XbaI fragments from the cloned pHannibal vector were transferred into the SalI/XbaI sites of the binary vector pE7p13M . pE7p13M was modified from pCAMBIA1300 (Hyg+) and carries the AtEXPA7 promoter at -480 bp from the transcription initiation site (Kim et al, 2006) (Fig. 1B).…”

“…2A). Many functional orthologs of AtEXPA7 (i.e., EXPA-like genes exhibiting root hair-specific expression) have been identified experimentally among monocots and eudicots (Kim et al, 2006). Recently, we identified two root hair-specific EXPBs in rice and barley (Won et al, 2010).…”

“…These genes encode proteins that may be specific for root hair growth in the Poaceae. Thus far, all root hair-specific EXPs carry root hair-specific ciselements (RHEs) in the proximal promoter region, indicating that these genes are subject to regulation by orthologous transcriptional components (Kim et al, 2006;Won et al, 2009;. However, the biological functions of these genes remain to be characterized in vivo.…”