Ethylene Modulates Flavonoid Accumulation and Gravitropic Responses in Roots of Arabidopsis

Abstract

Plant organs change their growth direction in response to reorientation relative to the gravity vector. We explored the role of ethylene in Arabidopsis (Arabidopsis thaliana) root gravitropism. Treatment of wild-type Columbia seedlings with the ethylene precursor 1-aminocyclopropane carboxylic acid (ACC) reduced root elongation and gravitropic curvature. The ethyleneinsensitive mutants ein2-5 and etr1-3 had wild-type root gravity responses, but lacked the growth and gravity inhibition by ACC found in the wild type. We examined the effect of ACC on tt4(2YY6) seedlings, which have a null mutation in the gene encoding chalcone synthase, the first enzyme in flavonoid synthesis. The tt4(2YY6) mutant makes no flavonoids, has elevated indole-3-acetic acid transport, and exhibits a delayed gravity response. Roots of tt4(2YY6), the backcrossed line tt4-2, and two other tt4 alleles had wild-type sensitivity to growth inhibition by ACC, whereas the root gravitropic curvature of these tt4 alleles was much less inhibited by ACC than wild-type roots, suggesting that ACC may reduce gravitropic curvature by altering flavonoid synthesis. ACC treatment induced flavonoid accumulation in root tips, as judged by a dye that becomes fluorescent upon binding flavonoids in wild type, but not in ein2-5 and etr1-3. ACC also prevented a transient peak in flavonoid synthesis in response to gravity. Together, these experiments suggest that elevated ethylene levels negatively regulate root gravitropism, using EIN2-and ETR1-dependent pathways, and that ACC inhibition of gravity response occurs through altering flavonoid synthesis.

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

“…Basipetal auxin transport may also be regulated by molecules affecting the activity, expression and subcellular localization of auxin transporters in the lateral cell files of the root (as reviewed by Muday and Rahman, 2007). In addition to auxin, other hormones or signaling molecules such as cytokinins (Aloni et al, 2004), reactive oxygen species (Joo et al, 2001), flavonoids and ethylene (Buer and Muday, 2004;Buer et al, 2006) may be involved in the growth response phase of gravitropism through control of differential elongation, either in parallel with auxin or as regulators of the auxin-mediated signaling pathway.…”

Auxin and Ethylene Induce Flavonol Accumulation through Distinct Transcriptional Networks

“…genetic evidence suggests that a variety of root developmental processes, including elongation, gravitropism, and lateral root formation, are regulated by cross talk between these two hormones (Rahman et al, 2001;Buer et al, 2006;Rů zicka et al, 2007;Stepanova et al, 2007;Swarup et al, 2007;Negi et al, 2008Negi et al, , 2010. The ethylene-and auxin-signaling pathways have been extensively studied, and studies employing global gene expression analyses and the unique genetic tools available in Arabidopsis (Arabidopsis thaliana) have identified a number of the key signaling proteins as well as the transcriptional response targets (Kendrick and Chang, 2008;Chapman and Estelle, 2009).…”

“…Genes encoding enzymes of flavonoid metabolism may be among these ultimate targets of auxin and ethylene transcriptional networks. Previous studies have suggested that flavonol accumulation may be induced by both auxin and ethylene and have implicated these specialized metabolites in hormone-dependent developmental pathways (Buer and Muday, 2004;Buer et al, 2006) but have not examined whether this accumulation is transcriptionally regulated.…”

Hormonal and Stress Induction of the Gene Encoding Common Bean Acetyl-Coenzyme A Carboxylase

“…In addition to oxylipins, ethylene has also been implicated in the activation of systemic plant defenses in response to pathogens (Penninckx et al, 1998) and wounding (O'Donnell et al, 1996). In Arabidopsis, ethylene also provokes an increase in flavonoid accumulation (Buer et al, 2006) and in carrot (Daucus carota) induces genes for flavonoid synthesis (Ecker and Davis, 1987). The JA and ethylene signaling pathways are induced concomitantly in Arabidopsis to activate defense responses after infection with a necrotrophic pathogen (Penninckx et al, 1998), but, after wounding, an antagonistic interaction between JA and ethylene was proposed for the local responses in Arabidopsis leaves (Rojo et al, 1999).…”