The vegetative juvenile-to-adult transition (vegetative phase change) is a critical phase in plant development, the timing of which is controlled by the highly conserved age pathway, comprising the miR156/miR157-SPL module and the downstream miR172-AP2-like module, and is modulated by exogenous and endogenous cues. The phytohormones cytokinin (CK) and gibberellin (GA) have been described to both alter miR172 levels, most probably by regulating SPL activity. In this study, we establish an epistatic relation between CK and GA, in which CK action depends on GA, contrasting with the antagonistic nature described previously for CK-GA crosstalk. We show that CK positively affects GA biosynthesis during Arabidopsis vegetative development and depends on the GA biosynthetic enzymes GA3ox1 and GA3ox2 to modify the appearance of abaxial trichomes as well as leaf shape, both hallmarks of vegetative phase change. Downstream of CK, epidermal identity is regulated in dependence of SPL transcription factors, the GA signaling repressors GAI and RGA and the miR172-targets TOE1 and TOE2. Notably, genetic analysis revealed that GA regulates this process also CK-independently. Furthermore, our data from genetic analyses suggests that CK affects leaf shape through other GA signaling components and AP2-like transcription factors rather than SPLs. Hence, CK differentially regulates several aspects of vegetative phase change. The work contributes to the understanding of vegetative phase change regulation as well as phytohormone crosstalk in general.

• MeSH
• Arabidopsis * metabolism   genetics   growth & development   MeSH
• Cytokinins * metabolism   MeSH
• Gibberellins * metabolism   MeSH
• Plant Leaves metabolism   growth & development   MeSH
• MicroRNAs metabolism   genetics   MeSH
• Mixed Function Oxygenases metabolism   genetics   MeSH
• Arabidopsis Proteins metabolism   genetics   MeSH
• Gene Expression Regulation, Plant MeSH
• Plant Growth Regulators metabolism   MeSH
• Signal Transduction MeSH
• Transcription Factors metabolism   genetics   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Cytokinins * MeSH
• GAI protein, Arabidopsis MeSH Browser
• Gibberellins * MeSH
• Nuclear Proteins MeSH
• MicroRNAs MeSH
• Mirn156 microRNA, Arabidopsis MeSH Browser
• Mixed Function Oxygenases MeSH
• Arabidopsis Proteins MeSH
• Plant Growth Regulators MeSH
• Repressor Proteins MeSH
• RGA protein, Arabidopsis MeSH Browser
• SPL protein, Arabidopsis MeSH Browser
• Transcription Factors MeSH

C-TERMINALLY ENCODED PEPTIDE (CEP) and cytokinin hormones act over short and long distances to control plant responses to environmental cues. CEP and cytokinin pathway mutants share phenotypes, however, it is not known if these pathways intersect. We show that CEP and cytokinin signalling converge on CEP DOWNSTREAM (CEPD) glutaredoxins to inhibit primary root growth. CEP inhibition of root growth was impaired in mutants defective in trans-zeatin (tZ)-type cytokinin biosynthesis, transport, perception, and output. Concordantly, mutants affected in CEP RECEPTOR 1 showed reduced root growth inhibition in response to tZ, and altered levels of tZ-type cytokinins. Grafting and organ-specific hormone treatments showed that tZ-mediated root growth inhibition involved CEPD activity in roots. By contrast, root growth inhibition by CEP depended on shoot CEPD function. The results demonstrate that CEP and cytokinin pathways intersect, and utilise signalling circuits in separate organs involving common glutaredoxin genes to coordinate root growth.

• MeSH
• Arabidopsis * metabolism   MeSH
• Cytokinins * metabolism   MeSH
• Glutaredoxins genetics   metabolism   MeSH
• Plant Roots metabolism   MeSH
• Peptides metabolism   MeSH
• Gene Expression Regulation, Plant MeSH
• Plant Shoots metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Cytokinins * MeSH
• Glutaredoxins MeSH
• Peptides MeSH

The epidermal cell layer of plants has important functions in regulating plant growth and development. We have studied the impact of an altered epidermal cytokinin metabolism on Arabidopsis shoot development. Increased epidermal cytokinin synthesis or breakdown was achieved through expression of the cytokinin synthesis gene LOG4 and the cytokinin-degrading CKX1 gene, respectively, under the control of the epidermis-specific AtML1 promoter. During vegetative growth, increased epidermal cytokinin production caused an increased size of the shoot apical meristem and promoted earlier flowering. Leaves became larger and the shoots showed an earlier juvenile-to-adult transition. An increased cytokinin breakdown had the opposite effect on these phenotypic traits indicating that epidermal cytokinin metabolism can be a factor regulating these aspects of shoot development. The phenotypic consequences of abbreviated cytokinin signaling in the epidermis achieved through expression of the ARR1-SRDX repressor were generally milder or even absent indicating that the epidermal cytokinin acts, at least in part, cell non-autonomously. Enhanced epidermal cytokinin synthesis delayed cell differentiation during leaf development leading to an increased cell proliferation and leaf growth. Genetic analysis showed that this cytokinin activity was mediated mainly by the AHK3 receptor and the transcription factor ARR1. We also demonstrate that epidermal cytokinin promotes leaf growth in a largely cell-autonomous fashion. Increased cytokinin synthesis in the outer layer of reproductive tissues and in the placenta enhanced ovule formation by the placenta and caused the formation of larger siliques. This led to a higher number of seeds in larger pods resulting in an increased seed yield per plant. Collectively, the results provide evidence that the cytokinin metabolism in the epidermis is a relevant parameter determining vegetative and reproductive plant growth and development.

• Keywords
• Arabidopsis, cytokinin, developmental transitions, epidermis, seed yield, shoot growth,
• Publication type
• Journal Article MeSH

We determined steady-state (basal) endogenous levels of three plant hormones (abscisic acid, cytokinins and indole-3-acetic acid) in a collection of thirty different ecotypes of Arabidopsis that represent a broad genetic variability within this species. Hormone contents were analysed separately in plant shoots and roots after 21 days of cultivation on agar plates in a climate-controlled chamber. Using advanced statistical and machine learning methods, we tested if basal hormonal levels can be considered a unique ecotype-specific classifier. We also explored possible relationships between hormone levels and the prevalent environmental conditions in the site of origin for each ecotype. We found significant variations in basal hormonal levels and their ratios in both root and shoot among the ecotypes. We showed the prominent position of cytokinins (CK) among the other hormones. We found the content of CK and CK metabolites to be a reliable ecotype-specific identifier. Correlation with the mean temperature at the site of origin and the large variation in basal hormonal levels suggest that the high variability may potentially be in response to environmental factors. This study provides a starting point for ecotype-specific genetic maps of the CK metabolic and signalling network to explore its contribution to the adaptation of plants to local environmental conditions.

• Keywords
• abscisic acid, cytokinin glucosides, cytokinin metabolism, cytokinins, indole-3-acetic acid, single nucleotide polymorphism,
• Publication type
• Journal Article MeSH

Five poplar CHASE-containing histidine kinase receptors bind cytokinins and display kinase activities. Both endogenous isoprenoid and aromatic cytokinins bind to the receptors in live cell assays. Cytokinins are phytohormones that play key roles in various developmental processes in plants. The poplar species Populus × canadensis, cv. Robusta, is the first organism found to contain aromatic cytokinins. Here, we report the functional characterization of five CHASE-containing histidine kinases from P. × canadensis: PcHK2, PcHK3a, PcHK3b, PcHK4a and PcHK4b. A qPCR analysis revealed high transcript levels of all PcHKs other than PcHK4b across multiple poplar organs. The ligand specificity was determined using a live cell Escherichia coli assay and we provide evidence based on UHPLC-MS/MS data that ribosides can be true ligands. PcHK2 exhibited higher sensitivity to iP-type cytokinins than the other receptors, while PcHK3a and PcHK3b bound these cytokinins much more weakly, because they possess two isoleucine residues that clash with the cytokinin base and destabilize its binding. All receptors display kinase activity but their activation ratios in the presence/absence of cytokinin differ significantly. PcHK4a displays over 400-fold higher kinase activity in the presence of cytokinin, suggesting involvement in strong responses to changes in cytokinin levels. trans-Zeatin was both the most abundant cytokinin in poplar and that with the highest variation in abundance, which is consistent with its strong binding to all five HKs and activation of cytokinin signaling via A-type response regulators. The aromatic cytokinins' biological significance remains unclear, their levels vary diurnally, seasonally, and annually. PcHK3 and PcHK4 display the strongest binding at pH 7.5 and 5.5, respectively, in line with their putative membrane localization in the endoplasmic reticulum and plasma membrane.

• Keywords
• Aromatic cytokinin, Histidine kinase, Hormone, Isoprenoid cytokinin, Poplar, Topolin,
• MeSH
• Cytokinins metabolism   MeSH
• Histidine Kinase metabolism   MeSH
• Populus metabolism   MeSH
• Tandem Mass Spectrometry MeSH
• Terpenes metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Cytokinins MeSH
• Histidine Kinase MeSH
• Terpenes MeSH

Cowpea (Vigna unguiculata [L.] Walp.) is a major crop for worldwide food and nutritional security, especially in sub-Saharan Africa, that is resilient to hot and drought-prone environments. An assembly of the single-haplotype inbred genome of cowpea IT97K-499-35 was developed by exploiting the synergies between single-molecule real-time sequencing, optical and genetic mapping, and an assembly reconciliation algorithm. A total of 519 Mb is included in the assembled sequences. Nearly half of the assembled sequence is composed of repetitive elements, which are enriched within recombination-poor pericentromeric regions. A comparative analysis of these elements suggests that genome size differences between Vigna species are mainly attributable to changes in the amount of Gypsy retrotransposons. Conversely, genes are more abundant in more distal, high-recombination regions of the chromosomes; there appears to be more duplication of genes within the NBS-LRR and the SAUR-like auxin superfamilies compared with other warm-season legumes that have been sequenced. A surprising outcome is the identification of an inversion of 4.2 Mb among landraces and cultivars, which includes a gene that has been associated in other plants with interactions with the parasitic weed Striga gesnerioides. The genome sequence facilitated the identification of a putative syntelog for multiple organ gigantism in legumes. A revised numbering system has been adopted for cowpea chromosomes based on synteny with common bean (Phaseolus vulgaris). An estimate of nuclear genome size of 640.6 Mbp based on cytometry is presented.

• Keywords
• Phaseolus vulgaris, Vigna unguiculata, chromosomal inversion, cowpea, domestication, genome annotation, genome evolution, genome size, legumes, next-generation sequencing, repetitive elements,
• MeSH
• Chromosomes, Plant genetics   MeSH
• Genome Size genetics   MeSH
• DNA, Plant chemistry   genetics   MeSH
• Phaseolus genetics   MeSH
• Genome, Plant genetics   MeSH
• Chromosome Mapping MeSH
• Retroelements genetics   MeSH
• Genes, Plant genetics   MeSH
• Sequence Analysis, DNA methods   MeSH
• Synteny MeSH
• Vigna genetics   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Names of Substances
• DNA, Plant MeSH
• Retroelements MeSH

BACKGROUND: Mal de Río Cuarto virus (MRCV) infects several monocotyledonous species including maize and wheat. Infected plants show shortened internodes, partial sterility, increased tillering and reduced root length. To better understand the molecular basis of the plant-virus interactions leading to these symptoms, we combined RNA sequencing with metabolite and hormone measurements. RESULTS: More than 3000 differentially accumulated transcripts (DATs) were detected in MRCV-infected wheat plants at 21 days post inoculation compared to mock-inoculated plants. Infected plants exhibited decreased levels of TaSWEET13 transcripts, which are involved in sucrose phloem loading. Soluble sugars, starch, trehalose 6-phosphate (Tre6P), and organic and amino acids were all higher in MRCV-infected plants. In addition, several transcripts related to plant hormone metabolism, transport and signalling were increased upon MRCV infection. Transcripts coding for GA20ox, D14, MAX2 and SMAX1-like proteins involved in gibberellin biosynthesis and strigolactone signalling, were reduced. Transcripts involved in jasmonic acid, ethylene and brassinosteroid biosynthesis, perception and signalling and in auxin transport were also altered. Hormone measurements showed that jasmonic acid, brassinosteroids, abscisic acid and indole-3-acetic acid were significantly higher in infected leaves. CONCLUSIONS: Our results indicate that MRCV causes a profound hormonal imbalance that, together with alterations in sugar partitioning, could account for the symptoms observed in MRCV-infected plants.

• Keywords
• Disease symptoms, Fijivirus, MRCV, Plant hormones, Reoviridae, SWEET transporters, Sucrose metabolism, Trehalose 6-phosphate, Wheat,
• MeSH
• Brassinosteroids metabolism   MeSH
• Sugars metabolism   MeSH
• Cytokinins metabolism   MeSH
• Gibberellins metabolism   MeSH
• Host-Pathogen Interactions physiology   MeSH
• Indoleacetic Acids metabolism   MeSH
• Plant Leaves metabolism   virology   MeSH
• Plant Diseases virology   MeSH
• Triticum genetics   metabolism   virology   MeSH
• Gene Expression Regulation, Plant MeSH
• Plant Growth Regulators metabolism   MeSH
• Reoviridae pathogenicity   MeSH
• Gene Expression Profiling MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Brassinosteroids MeSH
• Sugars MeSH
• Cytokinins MeSH
• Gibberellins MeSH
• Indoleacetic Acids MeSH
• Plant Growth Regulators MeSH