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Plant primary microRNA (miRNA) transcripts (pri-miRNAs) are not just a source of miRNAs but can also encode regulatory peptides (miPEPs) that enhance the accumulation, and so the effect, of the corresponding mature miRNAs—an observation that may have agronomical applications. miRNA transcripts MicroRNAs (miRNAs) are known primarily for inhibiting the expression of their target genes at the level of the messenger RNA. They arise from processing of much larger primary transcripts (pri-miRNAs). Jean-Philippe Combier and colleagues provide data suggesting that pri-miRNAs — in plants at least — are not just a source of miRNAs but can also encode regulatory peptides (miPEPs). In a further twist, the miPEPs arising from pri-miRNAs seem to enhance the accumulation, and hence the effect, of the associated mature miRNAs. The authors demonstrate the role of two such peptides, miPEP171b and miPEP165a, in plant root development. They also identify an additional five active miPEPs, hinting at the generality of this phenomenon. These observations may have agronomical applications, as synthetic miPEP171b and miPEP165a generated by these researchers and introduced into plants followed the same molecular path and had similar effects on root development as their natural counterparts. MicroRNAs (miRNAs) are small regulatory RNA molecules that inhibit the expression of specific target genes by binding to and cleaving their messenger RNAs or otherwise inhibiting their translation into proteins 1 . miRNAs are transcribed as much larger primary transcripts (pri-miRNAs), the function of which is not fully understood. Here we show that plant pri-miRNAs contain short open reading frame sequences that encode regulatory peptides. The pri-miR171b of Medicago truncatula and the pri-miR165a of Arabidopsis thaliana produce peptides, which we term miPEP171b and miPEP165a, respectively, that enhance the accumulation of their corresponding mature miRNAs, resulting in downregulation of target genes involved in root development. The mechanism of miRNA-encoded peptide (miPEP) action involves increasing transcription of the pri-miRNA. Five other pri-miRNAs of A. thaliana and M. truncatula encode active miPEPs, suggesting that miPEPs are widespread throughout the plant kingdom. Synthetic miPEP171b and miPEP165a peptides applied to plants specifically trigger the accumulation of miR171b and miR165a, leading to reduction of lateral root development and stimulation of main root growth, respectively, suggesting that miPEPs might have agronomical applications.

Citrus bacterial canker (CBC) results from Xanthomonas citri subsp. citri ( Xcc ) infection and poses a grave threat to citrus production. Class III peroxidases (CIII Prxs) are key proteins to the environmental adaptation of citrus plants to a range of exogenous pathogens, but the role of CIII Prxs during plant resistance to CBC is poorly defined. Herein, we explored the role of CsPrx25 and its contribution to plant defenses in molecular detail. Based on the expression analysis, CsPrx25 was identified as an apoplast-localized protein that is differentially regulated by Xcc infection, salicylic acid, and methyl jasmone acid in the CBC-susceptible variety Wanjincheng ( C. sinensis ) and the CBC-resistant variety Calamondin ( C. madurensis ). Transgenic Wanjincheng plants overexpressing CsPrx25 were generated, and these transgenic plants exhibited significantly increased CBC resistance compared with the WT plants. In addition, the CsPrx25 -overexpressing plants displayed altered reactive oxygen species (ROS) homeostasis accompanied by enhanced H 2 O 2 levels, which led to stronger hypersensitivity responses during Xcc infection. Moreover, the overexpression of CsPrx25 enhanced lignification as an apoplastic barrier for Xcc infection. Taken together, the results highlight how CsPrx25-mediated ROS homeostasis reconstruction and cell wall lignification can enhance the resistance of sweet orange to CBC.

Root hair polar growth is endogenously controlled by auxin and sustained by oscillating levels of reactive oxygen species (ROS). These cells extend several hundred-fold their original size toward signals important for plant survival. Although their final cell size is of fundamental importance, the molecular mechanisms that control it remain largely unknown. Here we show that ROS production is controlled by the transcription factor RSL4, which in turn is transcriptionally regulated by auxin through several auxin response factors (ARFs). In this manner, auxin controls ROS-mediated polar growth by activating RSL4, which then up-regulates the expression of genes encoding NADPH oxidases (also known as RESPIRATORY BURST OXIDASE HOMOLOG proteins) and class III peroxidases, which catalyze ROS production. Chemical or genetic interference with ROS balance or peroxidase activity affects root hair final cell size. Overall, our findings establish amolecular link between auxin and ROS-mediated polar root hair growth.

Colonization of land by plants was a major transition on Earth, but the developmental and genetic innovations required for this transition remain unknown. Physiological studies and the fossil record strongly suggest that the ability of the first land plants to form symbiotic associations with beneficial fungi was one of these critical innovations. In angiosperms, genes required for the perception and transduction of diffusible fungal signals for root colonization and for nutrient exchange have been characterized. However, the origin of these genes and their potential correlation with land colonization remain elusive. A comprehensive phylogenetic analysis of 259 transcriptomes and 10 green algal and basal land plant genomes, coupled with the characterization of the evolutionary path leading to the appearance of a key regulator, a calcium- and calmodulin-dependent protein kinase, showed that the symbiotic signaling pathway predated the first land plants. In contrast, downstream genes required for root colonization and their specific expression pattern probably appeared subsequent to the colonization of land. We conclude that the most recent common ancestor of extant land plants and green algae was preadapted for symbiotic associations. Subsequent improvement of this precursor stage in early land plants through rounds of gene duplication led to the acquisition of additional pathways and the ability to form a fully functional arbuscular mycorrhizal symbiosis.

Several physiological functions have been attributed to class III peroxidases (PRXs) in plants, but the in planta role of most members of this family still remains undetermined. Here, we report the first functional characterization of PRX17 (At2g22420), one of the 73 members of this family in Arabidopsis thaliana. Localization of PRX17 was examined by transient expression in Nicotiana benthamiana. Loss- and gain-of-function mutants in A. thaliana were studied. Regulation at the gene and protein levels was analyzed using β-glucuronidase (GUS) activity, quantitative reverse transcriptase (qRT)-PCR, zymography, and chromatin immunoprecipitation. Phenotypes were characterized including lignin and xylan contents. PRX17 was expressed in various tissues, including vascular tissues, and PRX17 was localized to the cell wall. In prx17, the lignin content was reduced in the stem and siliques and bolting was delayed, while the opposite phenotype was observed in 35S:PRX17 plants, together with a significant increase of lignin and xylan immunofluorescence signal. Finally, we demonstrated that the transcription factor AGAMOUS-LIKE15 (AGL15) binds to the PRX17 promoter and regulates PRX17 expression level. This converging set of structural, transcriptomic and physiological data suggests that PRX17, under the control of AGL15, contributes to developmental programs by playing an essential role in regulating age-dependent lignified tissue formation, including changes in cell wall properties.

• The aims of this study were to investigate the appearance of strigolactones in the green lineage and to determine the primitive function of these molecules. • We measured the strigolactone content of several isolated liverworts, mosses, charophyte and chlorophyte green algae using a sensitive biological assay and LC‐MS/MS analyses. In parallel, sequence comparison of strigolactone‐related genes and phylogenetic analyses were performed using available genomic data and newly sequenced expressed sequence tags. The primitive function of strigolactones was determined by exogenous application of the synthetic strigolactone analog, GR24, and by mutant phenotyping. • Liverworts, the most basal Embryophytes and Charales, one of the closest green algal relatives to Embryophytes, produce strigolactones, whereas several other species of green algae do not. We showed that GR24 stimulates rhizoid elongation of Charales, liverworts and mosses, and rescues the phenotype of the strigolactone‐deficient Ppccd8 mutant of Physcomitrella patens. • These findings demonstrate that the first function of strigolactones was not to promote arbuscular mycorrhizal symbiosis. Rather, they suggest that the strigolactones appeared earlier in the streptophyte lineage to control rhizoid elongation. They may have been conserved in basal Embryophytes for this role and then recruited for the stimulation of colonization by glomeromycotan fungi.

Root Hairs (RHs) growth is influenced by endogenous and by external environmental signals that coordinately regulate its final cell size. We have recently determined that RH growth was unexpectedly boosted when Arabidopsis thaliana seedlings are cultivated at low temperatures. It was proposed that RH growth plasticity in response to low temperature was linked to a reduced nutrient availability in the media. Here, we explore the molecular basis of this RH growth response by using a Genome Wide Association Study (GWAS) approach using Arabidopsis thaliana natural accessions. We identify the poorly characterized PEROXIDASE 62 (PRX62) and a related protein PRX69 as key proteins under moderate low temperature stress. Strikingly, a cell wall protein extensin (EXT) reporter reveals the effect of peroxidase activity on EXT cell wall association at 10 °C in the RH apical zone. Collectively, our results indicate that PRX62, and to a lesser extent PRX69, are key apoplastic PRXs that modulate ROS-homeostasis and cell wall EXT-insolubilization linked to RH elongation at low temperature. Arabidopsis root hair growth is enhanced at low temperatures. Here the authors show that the class III peroxidases PRX62 and PRX69 modulate ROS homeostasis and cell wall characteristics, and promote root hair elongation at low temperature.

Arabidopsis seedlings growing on inclined agar surfaces exhibit characteristic root behaviours called 'waving' and 'skewing': the former consists of a series of undulations, whereas the latter is a deviation from the direction of gravity. Even though the precise basis of these growth patterns is not well understood, both gravity and the contact between the medium and the root are considered to be the major players that result in these processes. The influence of these forces on root surface-dependent behaviours can be verified by growing seedlings at different gel pitches: plants growing on vertical plates present roots with slight waving and skewing when compared with seedlings grown on plates held at minor angles of < 90°. However, other factors are thought to modulate root growth on agar; for instance, it has been demonstrated that the presence and concentration of certain compounds in the medium (such as sucrose) and of drugs able to modify the plant cell cytoskeleton also affect skewing and waving. The recent discovery of an active role of ethylene on surface-dependent root behaviour, and the finding of new mutants showing anomalous growth, pave the way for a more detailed description of these phenomena.

Background Plant class III peroxidases exist as a large multigenic family involved in numerous functions suggesting a functional specialization of each gene. However, few genes have been linked with a specific function. Consequently total peroxidase activity is still used in numerous studies although its relevance is questionable. Transcriptome analysis seems to be a promising tool to overcome the difficulties associated with the study of this family. Nevertheless available microarrays are not completely reliable for this purpose. We therefore used a macroarray dedicated to the 73 class III peroxidase genes of A. thaliana to identify genes potentially involved in flower and fruit development. Results The observed increase of total peroxidase activity during development was actually correlated with the induction of only a few class III peroxidase genes which supports the existence of a functional specialization of these proteins. We identified peroxidase genes that are predominantly expressed in one development stage and are probable components of the complex gene networks involved in the reproductive phase. An attempt has been made to gain insight into plausible functions of these genes by collecting and analyzing the expression data of different studies in plants. Peroxidase activity was additionally observed in situ in the silique dehiscence zone known to be involved in pod shattering. Because treatment with a peroxidase inhibitor delayed pod shattering, we subsequently studied mutants of transcription factors (TF) controlling this mechanism. Three peroxidases genes - AtPrx13 , AtPrx30 and AtPrx55- were altered by the TFs involved in pod shatter. Conclusions Our data illustrated the problems caused by linking only an increase in total peroxidase activity to any specific development stage or function. The activity or involvement of specific class III peroxidase genes needs to be assessed. Several genes identified in our study had not been linked to any particular development stage or function until now. Notably AtPrx13 , which is one of the peroxidase genes not present on commercially available microarrays. A systematic survey of class III peroxidase genes expression is necessary to reveal specific class III peroxidase gene functions and the regulation and evolution of this key multifunctional enzyme family. The approach used in this study highlights key individual genes that merit further investigation.

Several topics have been tackled: the diversity of cell wall polysaccharides and their roles during development [15,16,17]; the particular role of the arabinogalactan proteins (AGPs) [18,19]; the regulation of cell wall components biosynthesis, either at the transcriptional level [20] or at the biosynthesis level [21]; the role of the cell wall in signaling [22,23]; the remodeling of the cell wall in response to abiotic or biotic stress [24,25,26,27,28,29,30]; and a glance at the evolution of myxospermy in Brassicaceae [31]. Equisetum sp. which were assumed to belong to the oldest extant genus among vascular plants [15]; Miscanthus x giganteus, as a promising cold-tolerant C4 plant for biomass production [26]; Hordeum vulgare and Lolium multiflorum, as crop or fodder plants [16,28]; Craterostigma plantagineum, known as the resurrection plant, exhibiting a unique cell wall folding mechanism conferring the capacity to withstand drought [29]; Glycine max, a plant of the Leguminosae (Fabaceae) family of great agronomic interest, exhibiting root border cells, secreting a mucilage with specific characteristics [25]; Dionaea muscipula and Utricularia nelumbifolia, which are carnivorous plants [17,18]; and Bellis perennis, an Asteraceae commonly used to study embryogenesis [30]. [26] have demonstrated that the composition of Miscanthus x giganteus cell walls was modified upon cold exposure at the level of plasmodesmata, as revealed by transmission electron microscopy, infrared spectroscopy (FTIR) and biomechanical tests. [19] have further developed their model of regulation of calcium exchange between the extracellular space and the cytosol: the so-called molecular pinball machine located at the plasma membrane requires an auxin-activated proton pump, AGPs, calcium channels and auxin-efflux PIN proteins.