ARL2, ARG1 and PIN3 define a gravity signal transduction pathway in root statocytes

Abstract

SummaryALTERED RESPONSE TO GRAVITY1 (ARG1) and its paralog ARG1-LIKE2 (ARL2) are J-domain proteins that are required for normal root and hypocotyl gravitropism. In this paper, we show that both ARL2 and ARG1 function in a gravity signal transduction pathway with PIN3, an auxin efflux facilitator that is expressed in the statocytes. In gravi-stimulated roots, PIN3 relocalizes to the lower side of statocytes, a process that is thought to, in part, drive the asymmetrical redistribution of auxin toward the lower flank of the root. We show that ARL2 and ARG1 are required for PIN3 relocalization and asymmetrical distribution of auxin upon gravistimulation. ARL2 is expressed specifically in the root statocytes, where it localizes to the plasma membrane. Upon ectopic expression, ARL2 is also found at the cell plate of dividing cells during cytokinesis, an area of intense membrane dynamics. Mutations in ARL2 and ARG1 also result in auxin-related expansion of the root cap columella, consistent with a role for ARL2 and ARG1 in regulating auxin flux through the root tip. Together these data suggest that ARL2 and ARG1 functionally link gravity sensation in the statocytes to auxin redistribution through the root cap.

Draft genome of the peanut A-genome progenitor ( Arachis duranensis ) provides insights into geocarpy, oil biosynthesis, and allergens

“…S29, and Dataset S14). Three of these genes were identified in Arabidopsis by several lines of experimental evidence (19)(20)(21) to be involved in signal transduction and organ response (Fig. 3C).…”

“…3C). Further analysis based on previous functional studies (19,(21)(22)(23)(24)(25) identified 24 A. duranensis genes likely to be gravitropic, including 4 involved in gravity perception, 8 in signal transduction, and 12 in organ response (Fig. 3C and Dataset S15).…”

PIN Polar Targeting

“…After gravistimulation, PIN3 has been found to relocate to the lower side of columella cells, thus rerouting the auxin flow to the lower side of the root and triggering root bending (Friml et al, 2002b;Harrison and Masson, 2008). It is possible, although not demonstrated, that other environmental signals, such as light, trigger PIN polarity changes for mediating other developmental responses.…”

Do ARG1 and ARL2 form an actin-based gravity-signaling chaperone complex in root statocytes?

“…[3][4][5][6] ARG1 and ARL2 function in a gravitysignaling pathway that links gravistimulation to the accumulation of PIN3 within the PM at the lower side of the statocytes and a redistribution of auxin across the cap. [4][5][6] ARG1 and ARL2 are membrane-associated proteins. While ARG1 localizes throughout the endosomal/secretory pathway, ARL2 associates primarily with the PM, and both proteins are found at the cell plate during cytokinesis.…”

“…While ARG1 localizes throughout the endosomal/secretory pathway, ARL2 associates primarily with the PM, and both proteins are found at the cell plate during cytokinesis. 4,6 ARG1 and ARL2 contain J-domains near their N-termini. J-domain proteins typically function as molecular co-chaperones by interacting with HSC70, coupling substrate binding to HSC70 ATPase activity.…”