Ethylene–auxin interactions regulate lateral root initiation and emergence in Arabidopsis thaliana

Abstract

SummaryPlant root systems display considerable plasticity in response to endogenous and environmental signals. Auxin stimulates pericycle cells within elongating primary roots to enter de novo organogenesis, leading to the establishment of new lateral root meristems. Crosstalk between auxin and ethylene in root elongation has been demonstrated, but interactions between these hormones in root branching are not well characterized. We find that enhanced ethylene synthesis, resulting from the application of low concentrations of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), promotes the initiation of lateral root primordia. Treatment with higher doses of ACC strongly inhibits the ability of pericycle cells to initiate new lateral root primordia, but promotes the emergence of existing lateral root primordia: behaviour that is also seen in the eto1 mutation. These effects are correlated with decreased pericycle cell length and increased lateral root primordia cell width. When auxin is applied simultaneously with ACC, ACC is unable to prevent the auxin stimulation of lateral root formation in the root tissues formed prior to ACC exposure. However, in root tissues formed after transfer to ACC, in which elongation is reduced, auxin does not rescue the ethylene inhibition of primordia initiation, but instead increases it by several fold. Mutations that block auxin responses, slr1 and arf7 arf19, render initiation of lateral root primordia insensitive to the promoting effect of low ethylene levels, and mutations that inhibit ethylene-stimulated auxin biosynthesis, wei2 and wei7, reduce the inhibitory effect of higher ethylene levels, consistent with ethylene regulating root branching through interactions with auxin.

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.…”

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

“…Applications of exogenous ethylene have been shown to inhibit lateral root initiation only on roots that have formed in the presence of a treatment with the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC; Ivanchenko et al, 2008). The ethylene-induced inhibitory effect is not observed on roots formed prior to ACC treatment; in fact, in this instance, ethylene is observed to moderately promote the emergence of lateral roots.…”

“…6). The low levels of ethylene may support lateral root formation by up-regulating auxin biosynthesis, which promotes lateral root primordia initiation (Swarup et al, 2007;Ivanchenko et al, 2008). Loss of XBAT32 would result in a stabilization of ACSs and increased ethylene synthesis (Fig.…”

“…Based on our findings, a feasible explanation for only a partial rescue for xbat32 could be the presence of high levels of ethylene in the mutant plants. Several studies point to an interaction between ethylene and auxin during lateral root production (Stepanova et al, 2007;Swarup et al, 2007;Ivanchenko et al, 2008;Negi et al, 2008). High ethylene levels promote both acropetal and basipetal auxin transport (Negi et al, 2008), which affects auxin uploading into root cells of the elongation zone, thus resulting in reduced lateral root production (Negi et al, 2008).…”

Incompatibilidade de enxertia em Prunus

“…Segundo esses autores, após a enxertia, quando as conexões vasculares estão sendo estabelecidas, a auxina produzida na cultivar é translocada para o sistema radicular, onde atinge concentrações muito elevadas, que desencadeiam um processo de degradação e deterioração das raízes. Estudos convergentes ainda sugerem que os níveis elevados de auxina podem ser causados por uma síntese elevada de etileno (ALONI et al, 2010;MUDAY et al, 2012), hormônio que estimula, através de sua via de sinalização, a biossíntese de auxina em diferentes órgãos da planta, além, de aumentar a capacidade de transporte de auxina, pois regula a transcrição dos seus componentes de transporte, como AUX1 e PIN2 (IVANCHENKO et al, 2008;ALONI et al, 2010;MUDAY et al, 2012). O etileno pode ainda induzir estresse oxidativo pela produção de células reativas de oxigênio (ALONI et al, 2010;HURR et al, 2013), provocando crescimento reduzido e problemas de compatibilidade (MOGHADAM et al, 2012).…”