Ethylene regulates lateral root formation and auxin transport in Arabidopsis thaliana

Abstract

SummaryLateral root branching is a genetically defined and environmentally regulated process. Auxin is required for lateral root formation, and mutants that are altered in auxin synthesis, transport or signaling often have lateral root defects. Crosstalk between auxin and ethylene in root elongation has been demonstrated, but interactions between these hormones in the regulation of Arabidopsis lateral root formation are not well characterized. This study utilized Arabidopsis mutants altered in ethylene signaling and synthesis to explore the role of ethylene in lateral root formation. We find that enhanced ethylene synthesis or signaling, through the eto1-1 and ctr1-1 mutations, or through the application of 1-aminocyclopropane-1-carboxylic acid (ACC), negatively impacts lateral root formation, and is reversible by treatment with the ethylene antagonist, silver nitrate. In contrast, mutations that block ethylene responses, etr1-3 and ein2-5, enhance root formation and render it insensitive to the effect of ACC, even though these mutants have reduced root elongation at high ACC doses. ACC treatments or the eto1-1 mutation significantly enhance radiolabeled indole-3-acetic acid (IAA) transport in both the acropetal and the basipetal directions. ein2-5 and etr1-3 have less acropetal IAA transport, and transport is no longer regulated by ACC. DR5-GUS reporter expression is also altered by ACC treatment, which is consistent with transport differences. The aux1-7 mutant, which has a defect in an IAA influx protein, is insensitive to the ethylene inhibition of root formation. aux1-7 also has ACC-insensitive acropetal and basipetal IAA transport, as well as altered DR5-GUS expression, which is consistent with ethylene altering AUX1-mediated IAA uptake, and thereby blocking lateral root formation.

A Co-Opted Hormonal Cascade Activates Dormant Adventitious Root Primordia upon Flooding in Solanum dulcamara

“…While ARs may develop from preformed primordia upon flooding, in some species they are formed de novo during the flood period (Negi et al, 2010;Vidoz et al, 2010). Interestingly, this stress-induced AR initiation, too, is stimulated by ethylene, while initiation of LRs, which is highly similar to that of ARs from a developmental point of view, is usually inhibited by ethylene (Negi et al, 2008;Ivanchenko et al, 2008). This highlights the repeated linking of the ethylene pathway to adaptive growth responses during evolution.…”

Root system architecture: insights fromArabidopsisand cereal crops

“…Similar to cytokinin, this is thought to occur by altering auxin dynamics in the root, for example by modulating the action of the auxin influx carrier AUX1 [79,80]. Recently, treatment of Arabidopsis root tissues with the ethylene precursor 1-aminocyclopropane-1-carboxylic acid was also found to increase expression of the PIN3 and PIN7 auxin efflux transporters, thus promoting auxin transport towards the root apex and preventing the localized auxin accumulations needed to initiate lateral root formation [81].…”

Arabidopsis RING E3 Ligase XBAT32 Regulates Lateral Root Production through Its Role in Ethylene Biosynthesis

“…The ABA signaling mutant abscisic acid insensitive3 shows reduced lateral root formation in response to an auxin stimulus (Brady et al, 2003). Ethylene also inhibits lateral root production (Chilley et al, 2006;Fukaki et al, 2007;Negi et al, 2008). The regulatory effect of ethylene on lateral root production is auxin dependent (Stepanova et al, 2005;Ruzicka et al, 2007;Swarup et al, 2007).…”

“…The regulatory effect of ethylene on lateral root production is auxin dependent (Stepanova et al, 2005;Ruzicka et al, 2007;Swarup et al, 2007). High levels of ethylene alter auxin transport, which in turn affects auxin uploading into root cells, to ultimately inhibit lateral root production (Gazzarrini and McCourt, 2001;Negi et al, 2008). Enhanced ethylene response mutants such as polaris display reduced IAA accumulation in roots and are deficient in lateral root development (Chilley et al, 2006).…”