Auxin Perception Is Required for Arbuscule Development in Arbuscular Mycorrhizal Symbiosis

Most land plant species live in symbiosis with arbuscular mycorrhizal fungi. These fungi differentiate essential functional structures called arbuscules in root cortical cells from which mineral nutrients are released to the plant. We investigated the role of microRNA393 (miR393), an miRNA that targets several auxin receptors, in arbuscular mycorrhizal root colonization. Expression of the precursors of the miR393 was down-regulated during mycorrhization in three different plant species: Solanum lycopersicum, Medicago truncatula, and Oryza sativa. Treatment of S. lycopersicum, M. truncatula, and O. sativa roots with concentrations of synthetic auxin analogs that did not affect root development stimulated mycorrhization, particularly arbuscule formation. DR5-GUS, a reporter for auxin response, was preferentially expressed in root cells containing arbuscules. Finally, overexpression of miR393 in root tissues resulted in down-regulation of auxin receptor genes (transport inhibitor response1 and auxin-related F box) and underdeveloped arbuscules in all three plant species. These results support the conclusion that miR393 is a negative regulator of arbuscule formation by hampering auxin perception in arbuscule-containing cells

Redundant and Specific Roles of the ARGONAUTE Proteins AGO1 and ZLL in Development and Small RNA-Directed Gene Silencing

The Arabidopsis ARGONAUTE1 (AGO1) and ZWILLE/PINHEAD/AGO10 (ZLL) proteins act in the miRNA and siRNA pathways and are essential for multiple processes in development. Here, we analyze what determines common and specific function of both proteins. Analysis of ago1 mutants with partially compromised AGO1 activity revealed that loss of ZLL function re-establishes both siRNA and miRNA pathways for a subset of AGO1 target genes. Loss of ZLL function in ago1 mutants led to increased AGO1 protein levels, whereas AGO1 mRNA levels were unchanged, implicating ZLL as a negative regulator of AGO1 at the protein level. Since ZLL, unlike AGO1, is not subjected to small RNA-mediated repression itself, this cross regulation has the potential to adjust RNA silencing activity independent of feedback dynamics. Although AGO1 is expressed in a broader pattern than ZLL, expression of AGO1 from the ZLL promoter restored transgene PTGS and most developmental defects of ago1, whereas ZLL rescued only a few AGO1 functions when expressed from the AGO1 promoter, suggesting that the specific functions of AGO1 and ZLL are mainly determined by their protein sequence. Protein domain swapping experiments revealed that the PAZ domain, which in AGO1 is involved in binding small RNAs, is interchangeable between both proteins, suggesting that this common small RNA-binding domain contributes to redundant functions. By contrast, the conserved MID and PIWI domains, which are involved in 5′-end small RNA selectivity and mRNA cleavage, and the non-conserved N-terminal domain, to which no function has been assigned, provide specificity to AGO1 and ZLL protein function

An antagonistic function for Arabidopsis DCL2 in development and a new function for DCL4 in generating viral siRNAs

Plants contain more DICER-LIKE (DCL) enzymes and double-stranded RNA binding (DRB) proteins than other eukaryotes, resulting in increased small RNA network complexities. Analyses of single, double, triple and quadruple dcl mutants exposed DCL1 as a sophisticated enzyme capable of producing both microRNAs (miRNAs) and siRNAs, unlike the three other DCLs, which only produce siRNAs. Depletion of siRNA-specific DCLs results in unbalanced small RNA levels, indicating a redeployment of DCL/DRB complexes. In particular, DCL2 antagonizes the production of miRNAs and siRNAs by DCL1 in certain circumstances and affects development deleteriously in dcl1 dcl4 and dcl1 dcl3 dcl4 mutant plants, whereas dcl1 dcl2 dcl3 dcl4 quadruple mutant plants are viable. We also show that viral siRNAs are produced by DCL4, and that DCL2 can substitute for DCL4 when this latter activity is reduced or inhibited by viruses, pointing to the competitiveness of DCL2. Given the complexity of the small RNA repertoire in plants, the implication of each DCL, in particular DCL2, in the production of small RNAs that have no known function will constitute one of the next challenges

Strigolactones contribute to shoot elongation and to the formation of leaf margin serrations in Medicago truncatula R108

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Toward the discovery of maize cell wall genes involved in silage quality and capacity to biofuel production

Silage maize is Currently, with grazing, the basis of cattle feeding. In the near future, maize stover and cereal straws will also be a major Source of carbohydrates for sustainable biofuel production. The embedding of cell wall in lignins and the linkages between lignins, p-hydroxycinnamic acids, and arabinoxylans greatly influences cell wall properties, including the enzymatic degradability of structural polysaccharides in animal rumen or industrial fermenters. Breeding for higher silage quality and biofuel production will thus be based on the discovery of genetic traits involved in each component biosynthesis and deposition in each lignified tissue. Genes involved or putatively involved in the biosynthesis of the grass cell wall were searched for, including phenolic Compounds, cell wall carbohydrates and regulation factors. While most cytosolic steps of monolignol biosynthesis have been identified, most of lignin pathway genes belong to small multigene families which were all identified based on data available in the Maize Genomics Sequencing Project (MGSP) database. Cell wall carbohydrate genes were identified based on their Arabidopsis orthologs and previous research in C3 grasses by MITCHELL et al. (2007). Transcription and regulation factors of cell wall genes were similarly identified based their orthologs described both in Arabidopsis and woody species. All these genes were mapped in silico considering their physical position in the MGSP database. Physical positions of previously described QTL for cell wall degradability, lignin and p-hydroxycinnamic acid contents were also searched for based on the position of the flanking market in the MGSP database and distances between QTL and flanking markets. While only a few lignin pathway genes mapped to QTL positions, several colocalizations were shown between QTL and transcription factor physical positions. This last result is in agreement with expression Studies which highlighted that several genes in the lignin pathway are simultaneously under-expressed in lines with higher cell wall degradability, likely corroborating an upstream regulation rather than co-regulation phenomena. However, none of these possible candidate genes have yet been validated and many QTL still do not have relevant candidates. A lot of relevant candidate genes are still to be discovered among those involved in lignin pathway gene regulation, in regulation of lignified tissue assembly, and in cell wall carbohydrate biosynthesis and deposition. In addition, in spite of their critical involvement in maize cell wall assembly and degradability, genes involved in ferulic acid biosynthesis and linkages with other cell wall components are little known

Drosophila primary microRNA-8 encodes a microRNA-encoded peptide acting in parallel of miR-8

International audienceBackground : Recent genome-wide studies of many species reveal the existence of a myriad of RNAs differing in size, coding potential and function. Among these are the long non-coding RNAs, some of them producing functional small peptides via the translation of short ORFs. It now appears that any kind of RNA presumably has a potential to encode small peptides. Accordingly, our team recently discovered that plant primary transcripts of microRNAs ( pri-miRs ) produce small regulatory peptides (miPEPs) involved in auto-regulatory feedback loops enhancing their cognate microRNA expression which in turn controls plant development. Here we investigate whether this regulatory feedback loop is present in Drosophila melanogaster.Results : We perform a survey of ribosome profiling data and reveal that many pri-miRNAs exhibit ribosome translation marks. Focusing on miR-8, we show that pri-miR-8 can produce a miPEP-8. Functional assays performed in Drosophila reveal that miPEP-8 affects development when overexpressed or knocked down. Combining genetic and molecular approaches as well as genome-wide transcriptomic analyses, we show that miR-8 expression is independent of miPEP-8 activity and that miPEP-8 acts in parallel to miR-8 to regulate the expression of hundreds of genes. Conclusion : Taken together, these results reveal that several Drosophila pri-miRs exhibit translation potential. Contrasting with the mechanism described in plants, these data shed light on the function of yet undescribed primary-microRNA -encoded peptides in Drosophila and their regulatory potential on genome expression

SL analysis of rice root exudates.

<p>Root exudates from rice plants grown under phosphate starvation were analyzed with liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) using multiple reaction monitoring (MRM). Chromatograms of (<b>A</b>) transitions 347.2 > 233 and (<b>B</b>) 347.2>96.8 for orobanchol; (<b>C</b>) transitions 331.2> 234 and (<b>D</b>) 331.2>96.8 for 2'<i>-epi-</i>5-deoxystrigol; (<b>E</b>) transitions 361.2>247 and (<b>F</b>) 361.2>96.8 for three putative methoxy-5-deoxystrigol isomers; (<b>G</b>) the total ion count (TIC) showing of all measured transitions and where orobanchol (8.05 min), <i>ent</i>-2'-<i>epi</i>-5-deoxystrigol (12.51 min) and the three putative methoxy-5-deoxystrigol isomers (9.87; 10.33; 10.86 min) are visible.</p