Project description:In monocots other than the cereals maize and rice, the repertoire and diversity of microRNAs (miRNAs) and the populations of phased, secondary, small interfering RNAs (phasiRNAs) are poorly characterized. To remedy this, we sequenced small RNAs (sRNAs) from vegetative and dissected inflorescence tissue in 28 phylogenetically diverse monocots and from several early-diverging angiosperm lineages, as well as publicly available data from 10 additional monocot species. We annotated miRNAs, siRNAs and phasiRNAs across the monocot phylogeny, identifying miRNAs apparently lost or gained in the grasses relative to other monocot families, as well as a number of tRNA fragments misannotated as miRNAs. Using our miRNA database cleaned of these misannotations, we identified conservation at the 8th, 9th, 19th and 3’ end positions that we hypothesize are signatures of selection for processing, targeting, or Argonaute sorting. We show that 21-nt reproductive phasiRNAs are far more numerous in grass genomes than other monocots. Based on sequenced monocot genomes and transcriptomes, DICER-LIKE 5 (DCL5), important to 24-nt phasiRNA biogenesis, likely originated via gene duplication before the diversification of the grasses. This curated database of phylogenetically diverse monocot miRNAs, siRNAs, and phasiRNAs is the largest collection to date, and should facilitate continued exploration of small RNA diversification in flowering plants.
Project description:The phytohormone cytokinin plays a significant role in nearly all aspects of plant growth and development. Cytokinin signaling has primarily been studied in the dicot model Arabidopsis, with relatively little work done in monocots, which include rice (Oryza sativa) and other cereals of agronomic importance. The cytokinin signaling pathway is a phosphorelay comprised of the histidine kinase receptors (HKs), the authentic histidine phosphotransfer proteins (AHPs), and the type-B Response Regulators (ARRs). Two negative regulators of cytokinin signaling have been identified: the type-A ARRs, which are cytokinin primary response genes, and the pseudo histidine phosphotransfer proteins (PHPs), which lack the His residue required for phosphorelay. Here, we describe the role of the PHP genes from rice. Phylogenic analysis indicates that the PHPs are generally first found in the genomes of gymnosperms and that they arose independently in monocots and dicots. Consistent with this, the three rice PHPs fail to complement an Arabidopsis php mutant (ahp6). Disruption of the three PHPs results in a molecular phenotype consistent with these elements acting as negative regulators of basal cytokinin signaling, including the constitutive up-regulation of a number of type-A RR and cytokinin oxidase genes. The triple php mutant affects multiple aspects of rice growth and development, including shoot morphology, panicle architecture and seed fill. However, in contrast to Arabidopsis, disruption of the rice PHPs does not affect root vascular patterning, suggesting that while many aspects of key signaling networks are conserved between monocots and dicots, the molecular components regulating some processes are distinct.
Project description:This experiment probed for the presence of known Arabidopsis and rice microRNAs in total RNA samples derived from species representative of the major groups of land plants: Eudicots (Arabidopsis thaliana, Nicotiana benthamiana), monocots (Oryza satica, Triticum aestivum), magnoliids (Liriodendron tulipifera), gymnosperms (Pinus resinosa), ferns (Ceratopteris thalictroides), lycopods (Selaginella uncinata), and mosses (Polytrichum juniperinum). In most cases two technical or biological replicates were performed.
Project description:Daylength is an important seasonal cue, and genetic variation in the regulation of photoperiodism has been selected for in adapting wheat and barley to northern latitudes. Despite the importance of this trait, the mechanism by which monocot plants sense photoperiod is not known. We find in Brachypodium distachyon that photoperiodism is mediated by phytochromeC (phyC), a chromophore that acts as a molecular timer and measures the length of the night. The phyC signal is directly communicated to the circadian clock via the activity of EARLY FLOWERING3 (ELF3). ELF3 is a central regulator of photoperiodism, and elf3 mutants display a constitutive long day transcriptome. By coordinating an endogenous timer for night length perception with rhythmical circadian clock controlled gene expression, this mechanism resolves how Brachypodium, and likely other monocots, perceive photoperiod. Using ChIP-Seq, we detected that occupancy of ELF3 at various genomic regions varies in response to photoperiod and ZTime.