Cytokinin Interplay with Ethylene, Auxin, and Glucose Signaling Controls Arabidopsis Seedling Root Directional Growth    

Abstract

(A.M.J.) Optimal root architecture is established by multiple intrinsic (e.g. hormones) and extrinsic (e.g. gravity and touch) signals and is established, in part, by directed root growth. We show that asymmetrical exposure of cytokinin (CK) at the root tip in Arabidopsis (Arabidopsis thaliana) promotes cell elongation that is potentiated by glucose in a hexokinase-influenced, G proteinindependent manner. This mode of CK signaling requires the CK receptor, ARABIDOPSIS HISTIDINE KINASE4 and, at a minimum, its cognate type B ARABIDOPSIS RESPONSE REGULATORS ARR1, ARR10, and ARR11 for full responsiveness, while type A response regulators act redundantly to attenuate this CK response. Ethylene signaling through the ethylene receptor ETHYLENE RESISTANT1 and its downstream signaling element ETHYLENE INSENSITIVE2 are required for CKinduced root cell elongation. Negative and positive feedback loops are reinforced by CK regulation of the expression of the genes encoding these elements in both the CK and ethylene signaling pathways. Auxin transport facilitated by PIN-FORMED2 as well as auxin signaling through control of the steady-state level of transcriptional repressors INDOLE-3-ACETIC ACID7 (IAA7), IAA14, and IAA17 via TRANSPORT INHIBITOR RESPONSE1/AUXIN SIGNALING F-BOX PROTEIN are involved in CK-induced root cell elongation. This action lies downstream of ethylene and CK induction. Intrinsic signaling in this response operates independently of the extrinsic signal touch, although actin filament organization, which is important in the touch response, may be important for this response, since latrunculin B can induce similar growth. This root growth response may have adaptive significance, since CK responsiveness is inversely related to root coiling and waving, two root behaviors known to be important for fitness.

Spatiotemporal Analysis of Localized Circadian Arrhythmias in Plant Roots

“…The C-terminal motif of APRRs is involved in recognition of certain specific DNA for clock regulation Gendron et al, 2012). Moreover, the response regulators (RRs) accumulate near the lateral roots, where they regulate cytokinin signaling (Mason et al, 2004;Kushwah et al, 2011). Therefore, it is thought that phase reset of the circadian rhythm alters the mecha- nisms controlling plant hormone crosstalk to enable initiation of lateral root differentiation.…”

Hypocotyl Directional Growth in Arabidopsis: A Complex Trait

“…X-Gluc was prepared as 100 mg L 21 stock solution in N,Ndimethylformamide. All treatment concentrations for this study were chosen from previously published reports (Nakamura et al, 2004b;Deslauriers and Larsen, 2010;Kim et al, 2011;Kushwah et al, 2011;Vandenbussche et al, 2011).…”

“…Germinated seeds were then covered with a sterile glass coverslip to provide impenetrable obstacle. GUS activities were determined following the methods described previously (Kushwah et al, 2011) after 2 to 3 h for SAUR::GUS and after 4 to 6 h for TCH4::GUS. The experiment was performed three times yielding similar results.…”

Identification of key genes involved in root development of tomato using expressed sequence tag analysis

“…Over the years, a number of genes related to root development have been identified that are important for pattern formation, cell cycle, cell growth. Moreover several genes involved in hormonal basis of root development have also been characterized, especially auxin and ethylene (Kushwah et al 2011). Several root mutants have been identified from different plants like Arabidopsis (Busov et al 2008), rice (Kim et al 2007), maize (Hochholdinger et al 2004) wheat (Wang et al 2006) and tomato (Negi et al 2010).…”