Biology subjects

Lakehal, A.

Publications and source records attributed to Lakehal, A..

4 recordsLinked to original sources

bioRxiv2021

Jasmonate inhibits adventitious root initiation through transcriptional repression of CKX1 and activation of RAP2.6L transcription factor in Arabidopsis

Adventitious rooting is a de novo organogenesis process that enables plants to propagate clonally and cope with environmental stresses. Adventitious root initiation (ARI) is controlled by interconnected transcriptional and hormonal networks, but there is little knowledge of the genetic and molecular programs orchestrating these networks. Thus, we have applied genome-wide transcriptome profiling to elucidate the profound transcriptional reprogramming events preceding ARI. These reprogramming events are associated with downregulation of cytokinin (CK) signaling and response genes, which could be triggers for ARI. Interestingly, we found that CK free-base content declined during ARI, due to downregulation of de novo CK biosynthesis and upregulation of CK inactivation pathways. We also found that MYC2-dependent jasmonate (JA) signaling inhibits ARI by downregulating expression of the CYTOKININ OXIDASE/DEHYDROGENASE1 gene. We also demonstrated that JA and CK synergistically activate expression of RELATED to APETALA2.6 LIKE (RAP2.6L) transcription factor, and constitutive expression of this transcription factor strongly inhibits ARI. Collectively, our findings reveal that previously unknown genetic interactions between JA and CK play key roles in ARI

plant biology↗

bioRxiv2020

Light controls de novo adventitious root regeneration by modulating jasmonate and cytokinin homeostasis in Norway spruce hypocotyls

Vegetative propagation relies on the capacity of plants to regenerate de novo adventitious roots (ARs), a quantitative trait controlled by the interaction of endogenous factors such as hormones and environmental cues among which light plays a central role. However, the physiological and molecular components mediating light cues during AR initiation (ARI) remain largely elusive. We explored the effect of light spectral quality on ARI in de-rooted Norway spruce seedlings as well as on hormone metabolism with sensitive mass spectrometry-based methods. We coupled this to gene expression analysis to identify potential signaling pathways and to extensive anatomical characterization to investigate ARI at the cellular level. We showed that in contrast to white light and blue light, red light promoted ARI likely by reducing jasmonate (JA) and JA-isoleucine biosynthesis and repressing the accumulation of isopentyl-adenine-type cytokinins and abscisic acid. We confirmed that exogenously applied JA and/or CK inhibit ARI, and found that they possibly act in the same pathway. The negative effect of JA was confirmed at the histological level. We showed that JA represses the early events of ARI. In conclusion, RL promotes ARI by repressing the accumulation of the wound-induced phytohormones JA and CK. HighlightBlue and red light have an opposite effect on adventitious root initiation in Norway spruce hypocotyl, red light having a promoting effect by modulating hormone homeostasis.

plant biology↗

bioRxiv2019

Cytokinin induction by the Jasmonate-induced AP2/ERF115 represses adventitious rooting in Arabidopsis

Jasmonate (JA), an oxylipin-derived phytohormone, plays crucial roles not only in plant immunity and defense against herbivorous insects but also in plant growth and developmental processes, including regeneration and organogenesis. However, the mechanistic basis of its mode of action and precise role in integrating other signaling cues are poorly understood. Here we provide genetic evidences that JA signaling acts in both NINJA-dependent and -independent modulation of the transcriptional activity of MYC transcription factors involved in the inhibition of adventitious root initiation (ARI). Our data show that NINJA-dependent JA signaling in pericycle cells blocks early events of ARI. Moreover, transcriptomic comparison of ninja-1myc2-322B double mutant (which produce extremely few ARs) and wild type seedlings identified a novel molecular network governed by the APETALA2/ETHYLENE RESPONSE FACTOR 115 (ERF115) transcription factor. We demonstrate that JA-induced ERF115 activates the cytokinin signaling machinery and thereby represses ARI. Altogether, our results reveal a molecular network involving cooperative crosstalk between JA and CK machineries that inhibits ARI.

plant biology↗

bioRxiv2019

Molecular framework for TIR1/AFB-Aux/IAA-dependent auxin sensing controlling adventitious rooting in Arabidopsis

In Arabidopsis thaliana, canonical auxin-dependent gene regulation is mediated by 23 transcription factors from the AUXIN RESPONSE FACTOR (ARF) family, most of which interact with 29 auxin/indole acetic acid (Aux/IAA) repressors, themselves forming, in the presence of auxin, coreceptor complexes with one of six TRANSPORT INHIBITOR1/AUXIN-SIGNALLING F-BOX PROTEINS (TIR1/AFB). Different combinations of co-receptors drive specific sensing outputs, allowing auxin to control a myriad of processes. Considerable efforts have been made to discern the temporal and spatial specificity of auxin action. However, owing to a lack of obvious phenotype in single loss-of-function mutants in Aux/IAA genes, most genetic studies have relied on gain-of-function mutants, which are highly pleiotropic. In this article, we describe a molecular framework for the role of several members of the auxin sensing machinery. Using loss-of-function mutants, we demonstrate that TIR1 and AFB2 are positive regulators, whereas IAA6, IAA9 and IAA17 are negative regulators of adventitious root (AR) formation. The three Aux/IAA proteins interact with ARF6 and/or ARF8, which we have previously shown to be positive regulators of AR formation upstream of jasmonate, and likely repress their activity. Our data also suggest a dual role for TIR1 in the control of JA biosynthesis and conjugation, as revealed by upregulation of several JA biosynthesis genes in the tir1-1 mutant. In conclusion, we propose that in the presence of auxin, TIR1 and AFB2 form specific sensing complexes with IAA6, IAA9 and/or IAA17 that modulate JA homeostasis to control AR initiation.\n\nSignificanceAdventitious root (AR) formation is a quantitative trait with high phenotypic plasticity and auxin plays a major role in its control. In previous studies, we have shown that, in Arabidopsis hypocotyls, AR formation is negatively regulated by jasmonate, whose homeostasis is controlled by a regulatory module composed of three AUXIN RESPONSE FACTORS (ARF), two of which are positive regulators of three auxin inducible Gretchen Hagen3 (GH3) genes. The present work demonstrates that the two F-box proteins, i.e., TIR1 and AFB2, together with at least three Aux/IAA proteins are likely to interact in a combinatorial manner to control the activity of the two activator ARFs upstream of JA biosynthesis and/or homeostasis, thereby controlling AR initiation in Arabidopsis hypocotyls.

plant biology↗