Regulation of Root Hair Initiation and Expansin Gene Expression in Arabidopsis[W]

Abstract

The expression of two Arabidopsis expansin genes ( AtEXP7 and AtEXP18 ) is tightly linked to root hair initiation; thus, the regulation of these genes was studied to elucidate how developmental, hormonal, and environmental factors orchestrate root hair formation. Exogenous ethylene and auxin, as well as separation of the root from the medium, stimulated root hair formation and the expression of these expansin genes. The effects of exogenous auxin and root separation on root hair formation required the ethylene signaling pathway. By contrast, blocking the endogenous ethylene pathway, either by genetic mutations or by a chemical inhibitor, did not affect normal root hair formation and expansin gene expression. These results indicate that the normal developmental pathway for root hair formation (i.e., not induced by external stimuli) is independent of the ethylene pathway. Promoter analyses of the expansin genes show that the same promoter elements that determine cell specificity also determine inducibility by ethylene, auxin, and root separation. Our study suggests that two distinctive signaling pathways, one developmental and the other environmental/ hormonal, converge to modulate the initiation of the root hair and the expression of its specific expansin gene set.

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.…”

Haustorial Hairs Are Specialized Root Hairs That Support Parasitism in the Facultative Parasitic Plant Phtheirospermum japonicum

“…Other genes, like HHD2, regulate root hair elongation through the regulation of various cellular components. Such genes include COW1, MYA2, RHD2, EXPA7, RHS2, RSL2, and ACTIN2 (Cho and Cosgrove, 2002;Ringli et al, 2002;Foreman et al, 2003;Böhme et al, 2004;Peremyslov et al, 2008;Won et al, 2009;Yi et al, 2010). For example, a widely characterized cellular component involved in root hair elongation is ROS, which is produced by NADPH activity.…”

“…We first investigated Arabidopsis EXPANSIN7 (AtEXP7) and AtEXP18, which are expressed exclusively in root hairs and have been used as root hair marker genes (Cho and Cosgrove, 2002). The promoter regions of these genes contain a root hair-specific ciselement called RHE (for root hair element), which is functionally conserved among root hair genes in a wide range of angiosperms with distinct root hair distribution patterns (Kim et al, 2006).…”

Deep Sequencing of the Medicago truncatula Root Transcriptome Reveals a Massive and Early Interaction between Nodulation Factor and Ethylene Signals

“…Similarly, two expansins were up-regulated 6 hpi. Expansins are linked to root hair initiation in Arabidopsis and barley (Hordeum vulgare) and may be related to the reinitiation of polar growth during root hair branching (Cho and Cosgrove, 2002;Kwasniewski and Szarejko, 2006). Additionally, several b-glucanases were induced by 6 hpi.…”