Biology subjects

Mekkaoui, K.

Publications and source records attributed to Mekkaoui, K..

4 recordsLinked to original sources

bioRxiv2026

The role of MYB21 in Arabidopsis: transcending flower-specific functions to vegetative tissue

Jasmonic acid (JA) and its derivatives are lipid-derived phytohormones that coordinate plant growth, development, and stress responses through the bioactive conjugate jasmonoyl-isoleucine (JA-Ile). Their role in reproductive development is well established, particularly in stamen maturation through the R2R3-MYB transcription factor MYB21, which has been considered largely flower-specific. Here, we reveal a previously unrecognized role of MYB21 in vegetative tissues of Arabidopsis thaliana. Although basal MYB21 transcript levels in leaves are extremely low and spatially restricted, wounding and exogenous hormone applications induced MYB21 transcription in a JA- and COI1-dependent manner. Transcriptional GUS reporter analyses showed localized MYB21 promoter activity in specialized epidermal cells, including trichomes, hydathodes, and in the vasculature at wound sites. Functional characterization using the myb21-5 mutant indicated roles in germination and vegetative growth, partially phenocopying JA-insensitive mutants despite unaltered JA biosynthesis and signaling. Transcriptome profiling further revealed changes in expression of genes involved in lignin biosynthesis, light-harvesting complex components, cytokinin pathways, and defense-related responses, consistent with reduced resistance of myb21-5 to insect herbivory and infection by Botrytis cinerea. Together, these findings identify MYB21 as a JA-responsive regulator of growth and defense in seedlings and leaves, extending its function beyond reproductive development. HighlightThe transcription factor MYB21, previously considered flower-specific, is induced by jasmonate signaling in Arabidopsis leaves and seedlings, where it regulates growth and defense responses, thereby expanding its role beyond reproductive development.

plant biology↗

bioRxiv2024

Unraveling the Role of 12-cis-Oxo-Phytodienoic Acid in the Wound Response of Arabidopsis thaliana: Insights from Transcriptomic and Complementation Studies

12-cis-Oxo-phytodienoic acid (OPDA), the main precursor of the key plant growth and defense hormone jasmonoyl-isoleucine (JA-Ile), is believed to have distinct signaling roles in plants responses to stress. In Arabidopsis, insights into OPDA functions have been gained from studying a mutant, which is affected in the conversion of OPDA by missing OPDA REDUCTASE3 (OPR3). opr3 mutants, however, accumulate JA-Ile through a cytosolic bypass mediated by OPR2. Therefore, wound-induced transcriptome of opr2opr3 in comparison to wild-type and allene oxide synthase mutant was analyzed to unravel OPDA signaling. Results showed that OPDA lacked a distinct transcriptional signature, whereas known OPDA-response genes were wound-induced independently of OPDA. The application of OPDA to opr2opr3 resulted in a distinct transcriptional response compared to the endogenous rise of OPDA in the same mutant, with the activation of the sulfur assimilation pathway genes occurring only with the external application of the compound. These findings suggested a compartmentalization of endogenously produced OPDA, investigated further through trans-organellar complementation. OPR3 complemented opr2opr3 mutants in fertility and wound-induced JA-Ile production regardless of its localization. Since in vitro enzymatic studies revealed OPR3s activity on both OPDA and 4,5-ddh-JA, conclusions on translocation of OPDA were not unequivocal. Dissecting the conversion of either OPDA or 4,5-ddh-JA by OPR2 and OPR1 organelle variants pointed, however, to a strong OPDA compartmentalization supporting its lacking signaling function.

plant biology↗

bioRxiv2024

The modified activity of prolyl 4 hydroxylases (P4Hs) reveals the effect of arabinogalactan proteins (AGPs) on changes in the cell wall during the tomato ripening process

Arabinogalactan proteins (AGPs) are proteoglycans with an unusual molecular structure characterised by the presence of a protein part and carbohydrate chains. Their specific properties at different stages of the fruit ripening programme make AGPs unique markers of this process. An important function of AGPs is to co-form an amorphous extracellular matrix in the cell wall-plasma membrane continuum; thus, changes in the structure of these molecules can determine the presence and distribution of other components. The aim of the current work was to characterise the molecular structure and localisation of AGPs during the fruit ripening process in transgenic lines with silencing and overexpression of SlP4H3 genes. The objective was accomplished through comprehensive and comparative in situ and ex situ analyses of AGPs from the fruit of transgenic lines and wild-type plants at specific stages of ripening. The experiment showed that changes in P4H3 activity affected the content of AGPs and the progress in their modifications in the ongoing ripening process. The analysis of the transgenic lines confirmed the presence of AGPs with high molecular weights (120-60 kDa) at all the examined stages, but a changed pattern of the molecular features of AGPs was found in the last ripening stages, compared to WT. In addition to the AGP molecular changes, morphological modifications of fruit tissue and alterations in the spatio-temporal pattern of AGP distribution at the subcellular level were detected in the transgenic lines with the progression of the ripening process. The work highlights the irreversible impact of AGPs and their alterations on the fruit cell wall assembly and changes in AGPs associated with the progression of the ripening process. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=96 SRC="FIGDIR/small/576594v1_ufig1.gif" ALT="Figure 1"> View larger version (17K): org.highwire.dtl.DTLVardef@4291e4org.highwire.dtl.DTLVardef@780fdeorg.highwire.dtl.DTLVardef@59c14borg.highwire.dtl.DTLVardef@a12735_HPS_FORMAT_FIGEXP M_FIG C_FIG

plant biology↗

bioRxiv2021

A tomato prolyl-4-hydroxylase causes relocation of abscission zone and alters abscission kinetics

The detachment of organs is controlled by highly regulated molecular mechanisms. The position of the tomato abscission zone (AZ) is defined by the ratio of the proximal to distal part of the pedicel. In this study, the ratio was altered due to a shift in the position of the AZ which was attributed to shorter and longer pedicels of SlP4H3 RNAi and OEX lines due to changes on cell division and expansion in AZ and distal part. This might be associated with LM2- and JIM8-AGPs which increased in OEX and decreased in RNAi lines throughout the pedicel. The JIM13 AGPs were downregulated in the flower AZ of OEX lines, pointing to a role on abscission regulation. In addition, Co-IP in flower AZ with SlP4H3-GFP fusion proteins showed interaction with LM2-, JIM13- and JIM8-epitopes suggesting proline hydroxylation by SlP4H3. The lower content of methyl-esterified HGs and higher of demethyl-esterified HGs in the AZs of RNAi lines might be responsible for increased rigidity of the AZ cell walls, accounting for the higher force required for AZ tissue detachment to occur. Moreover, ethylene-induced flower abscission was accelerated in the RNAi lines and delayed in OEX lines, while exactly the opposite response was observed in the red ripe fruit AZs. This was partly attributed to alterations in the expression of cell wall hydrolases. Overall, these results indicate that P4Hs might regulate molecular and structural features of cell walls in the AZ as well as abscission progression by regulating the structure and function of AGPs. Sentence SummaryAlterations on the expression of tomato prolyl 4 hydroxylase 3 shifts the position of the pedicel abscission zone and alters ethylene induced abscission progression according to the developmental context of the pedicel.

plant biology↗