MADS-complexes regulate transcriptome dynamics during pollen maturation

Pollen transcript profiling of mutants defective in MADS-domain MIKC* protein complexes suggests they control a transcriptional network directing cellular differentiation during pollen maturation

Evolution of MIR168 paralogs in Brassicaceae

<p>Abstract</p> <p>Background</p> <p>In plants, expression of ARGONAUTE1 (AGO1), the catalytic subunit of the RNA-Induced Silencing Complex responsible for post-transcriptional gene silencing, is controlled through a feedback loop involving the miR168 microRNA. This complex auto-regulatory loop, composed of miR168-guided AGO1-catalyzed cleavage of <it>AGO1 </it>mRNA and AGO1-mediated stabilization of miR168, was shown to ensure the maintenance of AGO1 homeostasis that is pivotal for the correct functioning of the miRNA pathway.</p> <p>Results</p> <p>We applied different approaches to studying the genomic organization and the structural and functional evolution of <it>MIR168 </it>homologs in Brassicaeae. A whole genome comparison of Arabidopsis and poplar, phylogenetic footprinting and phylogenetic reconstruction were used to date the duplication events originating <it>MIR168 </it>homologs in these genomes. While orthology was lacking between Arabidopsis and poplar <it>MIR168 </it>genes, we successfully isolated orthologs of both loci present in Arabidopsis (<it>MIR168a </it>and <it>MIR168b</it>) from all the Brassicaceae species analyzed, including the basal species <it>Aethionema grandiflora</it>, thus indicating that (1) independent duplication events took place in Arabidopsis and poplar lineages and (2) the origin of <it>MIR168 </it>paralogs predates both the Brassicaceae radiation and the Arabidopsis alpha polyploidization. Different phylogenetic footprints, corresponding to known functionally relevant regions (transcription starting site and double-stranded structures responsible for microRNA biogenesis and function) or for which functions could be proposed, were found to be highly conserved among <it>MIR168 </it>homologs. Comparative predictions of the identified microRNAs also indicate extreme conservation of secondary structure and thermodynamic stability.</p> <p>Conclusion</p> <p>We used a comparative phylogenetic footprinting approach to identify the structural and functional constraints that shaped <it>MIR168 </it>evolution in Brassicaceae. Although their duplication happened at least 40 million years ago, we found evidence that both <it>MIR168 </it>paralogs have been maintained throughout the evolution of Brassicaceae, most likely functionally as indicated by the extremely high conservation of functionally relevant regions, predicted secondary structure and thermodynamic profile. Interestingly, the expression patterns observed in Arabidopsis indicate that <it>MIR168b </it>underwent partial subfunctionalization as determined by the experimental characterization of its expression pattern provided in this study. We found further evolutionary evidence that pre-miR168 lower stem (the RNA-duplex structure adjacent to the miR-miR* stem) is significantly longer than animal lower stems and probably plays a relevant role in multi-step miR168 biogenesis.</p

The microRNA regulated SBP-box genes SPL9 and SPL15 control shoot maturation in Arabidopsis

Throughout development the Arabidopsis shoot apical meristem successively undergoes several major phase transitions such as the juvenile-to-adult and floral transitions until, finally, it will produce flowers instead of leaves and shoots. Members of the Arabidopsis SBP-box gene family of transcription factors have been implicated in promoting the floral transition in dependence of miR156 and, accordingly, transgenics constitutively over-expressing this microRNA are delayed in flowering. To elaborate their roles in Arabidopsis shoot development, we analysed two of the 11 miR156 regulated Arabidopsis SBP-box genes, i.e. the likely paralogous genes SPL9 and SPL15. Single and double mutant phenotype analysis showed these genes to act redundantly in controlling the juvenile-to-adult phase transition. In addition, their loss-of-function results in a shortened plastochron during vegetative growth, altered inflorescence architecture and enhanced branching. In these aspects, the double mutant partly phenocopies constitutive MIR156b over-expressing transgenic plants and thus a major contribution to the phenotype of these transgenics as a result of the repression of SPL9 and SPL15 is strongly suggested

SBP-domain transcription factors as possible effectors of cryptochrome-mediated blue light signalling in the moss Physcomitrella patens

Cryptochromes are blue light absorbing photoreceptors found in many organisms and involved in numerous developmental processes. At least two highly similar cryptochromes are known to affect branching during gametophytic development in the moss Physcomitrella patens. We uncovered a relationship between these cryptochromes and the expression of particular members of the SBP-box genes, a plant specific transcription factor family. Transcript levels of the respective moss SBP-box genes, all belonging to the LG1-subfamily, were found to be dependent, albeit not exclusively, on blue light. Moreover, disruptant lines generated for two moss representatives of this SBP-box gene subfamily, both showed enhanced caulonema side branch formation, a phenotype opposite to that of the ppcry1a/1b double disruptant line. In this report we show that PpCRY1a and PpCRY1b act negatively on the transcript levels of several related moss SBP-box genes and that at least PpSBP1 and PpSBP4 act as negative regulators of side branch formation

Freier Zugang zu genetischen Pflanzenressourcen

Weisshaar B, Saedler H. Freier Zugang zu genetischen Pflanzenressourcen. GenomXPress. 2005;2005(3):7-9.Die im Rahmen der deutschen Pflanzengenom-Initiative GABI (Genomanalyse im biologischen System Pflanze) am Kölner Max-Planck-Institut für Züchtungsforschung erstellten GABI-Kat-Linien werden an ein internationales Zentrum für pflanzliche Ressourcen übergeben und damit weltweit frei zugänglich gemacht. Bei den GABI-Kat-Linien handelt es sich um eine Sammlung genau definierter und katalogisierter Gendefekt-Mutanten der Referenzpflanze Arabidopsis thaliana. Das Studium der GABI-Kat-Linien führt Wissenschaftler zur Funktion der jeweils betroffenen Gene und deren Beitrag zu wichtigen pflanzlichen Eigenschaften. In Kulturpflanzen kann damit genau und schnell nach besseren Varianten wichtiger Gene gesucht werden, um so neue Pflanzensorten zu züchten, die z. B. Pilzattacken abwehren, Dürre und Frost widerstehen oder höhere Erträge bei geringerer Düngung liefern

Heterotopic expression of MPF2 is the key to the evolution of the Chinese lantern of Physalis, a morphological novelty in Solanaceae

Morphological novelties arise through changes in development, but the underlying causes of such changes are largely unknown. In the genus Physalis, sepals resume growth after pollination to encapsulate the mature fruit, forming the “Chinese lantern,” a trait also termed inflated-calyx syndrome (ICS). STMADS16, which encodes a MADS-box transcription factor, is expressed only in vegetative tissues in Solanum tuberosum. Its ortholog in Physalis pubescens, MPF2, is expressed in floral tissues. Knockdown of MPF2 function in Physalis by RNA interference (RNAi) reveals that MPF2 function is essential for the development of the ICS. The phenotypes of transgenic S. tuberosum plants that overexpress MPF2 or STMADS16 corroborate these findings: these plants display enlarged sepals. Although heterotopic expression of MPF2 is crucial for ICS, remarkably, fertilization is also required. Although the ICS is less prominent or absent in the knockdown transgenic plants, epidermal cells are larger, suggesting that MPF2 exerts its function by inhibiting cell elongation and promoting cell division. In addition, severely affected Physalis knockdown lines are male sterile. Thus, heterotopic expression of MPF2 in floral tissues is involved in two novel traits: expression of the ICS and control of male fertility. Sequence differences between the promoter regions of the MPF2 and STMADS16 genes perhaps reflect exposure to different selection pressures during evolution, and correlate with the observed differences in their expression patterns. In any case, the effects of heterotopic expression of MPF2 underline the importance of recruitment of preexisting transcription factors in the evolution of novel floral traits

The En/Spm transposable element system of Zea mays

<div>Lecture given by Professor Heinz Saedler, Director, Max-Planck-Institut für Züchtungsforschung, Köln, Germany at the Waite Campus, University of Adelaide, 5.7.</div><div><br></div><p>This lecture is part of the Campus Seminars and Distinguished Lecturer Series, Waite Campus, University of Adelaide, 1991 – 1997. </p> <a href="https://figshare.com/projects/Campus_Seminars_and_Distinguished_Lecturer_Series_Waite_Campus_University_of_Adelaide/17756">https://figshare.com/projects/Campus_Seminars_and_Distinguished_Lecturer_Series_Waite_Campus_University_of_Adelaide/17756</a

MIKC* MADS-Protein Complexes Bind Motifs Enriched in the Proximal Region of Late Pollen-Specific Arabidopsis Promoters

The genome of Arabidopsis (Arabidopsis thaliana) encodes over 100 MADS-domain transcription factors, categorized into five phylogenetic subgroups. Most research efforts have focused on just one of these subgroups (MIKC(c)), whereas the other four remain largely unexplored. Here, we report on five members of the so-called Mδ or Arabidopsis MIKC* (AtMIKC*) subgroup, which are predominantly expressed during the late stages of pollen development. Very few MADS-box genes function in mature pollen, and from this perspective, the AtMIKC* genes are therefore highly exceptional. We found that the AtMIKC* proteins are able to form multiple heterodimeric complexes in planta, and that these protein complexes exhibit a for the MADS-family unusual and high DNA binding specificity in vitro. Compared to their occurrence in promoters genome wide, AtMIKC* binding sites are strongly overrepresented in the proximal region of late pollen-specific promoters. By combining our experimental data with in silico genomics and pollen transcriptomics approaches, we identified a considerable number of putative direct target genes of the AtMIKC* transcription factor complexes in pollen, many of which have known or proposed functions in pollen tube growth. The expression of several of these predicted targets is altered in mutant pollen in which all AtMIKC* complexes are affected, and in vitro germination of this mutant pollen is severely impaired. Our data therefore suggest that the AtMIKC* protein complexes play an essential role in transcriptional regulation during late pollen development