SUMMARY
DELAY OF GERMINATION 1 is a key regulator of dormancy in flowering plants before seed germination. Bryophytes develop haploid spores with an analogous function to seeds. Here, we investigate ...whether DOG1 function during germination is conserved between bryophytes and flowering plants and analyse the underlying mechanism of DOG1 action in the moss Physcomitrium patens. Phylogenetic and in silico expression analyses were performed to identify and characterise DOG1 domain‐containing genes in P. patens. Germination assays were performed to characterise a Ppdog1‐like1 mutant, and replacement with AtDOG1 was carried out. Yeast two‐hybrid assays were used to test the interaction of the PpDOG1‐like protein with DELLA proteins from P. patens and A. thaliana. P. patens possesses nine DOG1 domain‐containing genes. The DOG1‐like protein PpDOG1‐L1 (Pp3c3_9650) interacts with PpDELLAa and PpDELLAb and the A. thaliana DELLA protein AtRGA in yeast. Protein truncations revealed the DOG1 domain as necessary and sufficient for interaction with PpDELLA proteins. Spores of Ppdog1‐l1 mutant germinate faster than wild type, but replacement with AtDOG1 reverses this effect. Our data demonstrate a role for the PpDOG1‐LIKE1 protein in moss spore germination, possibly alongside PpDELLAs. This suggests a conserved DOG1 domain function in germination, albeit with differential adaptation of regulatory networks in seed and spore germination.
Significance Statement
Seed and spore germination are considered analogous because they occur in the sporophyte (seed plants) and gametophyte (bryophytes). Here we show that an ortholog of Arabidopsis DELAY OF GERMINATION 1 (DOG1) controls spore germination in the moss P. patens, suggesting deep evolutionary conservation of germination control of reproductive diaspores.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
42.
Phytochromes: More Than Meets the Eye Rensing, Stefan A; Sheerin, David J; Hiltbrunner, Andreas
Trends in plant science
21, Issue:
7
Journal Article
Peer reviewed
Phytochromes play a key role in the regulation of plant growth and development. Phytochrome-related proteins also occur in some bacteria, fungi, and algae. We highlight recent findings on the ...evolution of phytochromes and discuss novel hypotheses on the function of phytochromes in diatoms, a group of mainly pelagic algae.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The guided entry of tail-anchored proteins (GET) pathway facilitates targeting and insertion of tail-anchored proteins into membranes. In plants, such a protein insertion machinery for the ...endoplasmic reticulum as well as constituents within mitochondrial and chloroplasts were discovered. Previous phylogenetic analysis revealed that Get3 sequences of Embryophyta form two clades representing cytosolic (“a”) and organellar (“bc”) GET3 homologs, respectively. Cellular fractionation of Arabidopsis thaliana seedlings and usage of the self-assembly GFP system in protoplasts verified the cytosolic (ATGet3a), plastidic (ATGet3b) and mitochondrial (ATGet3c) localization of the different homologs. The identified plant homologs of Get1 and Get4 in A. thaliana are localized in ER and cytosol, respectively, implicating a degree of conservation of the GET pathway in A. thaliana. Transient expression of Get3 homologs of Solanum lycopersicum, Medicago × varia or Physcomitrella patens with the self-assembly GFP technique in homologous and heterologous systems verified that multiple Get3 homologs with differing subcellular localizations are common in plants. Chloroplast localized Get3 homologs were detected in all tested plant systems. In contrast, mitochondrial localized Get3 homologs were not identified in S. lycopersicum, or P. patens, while we confirmed on the example of A. thaliana proteins that mitochondrial localized Get3 proteins are properly targeted in S. lycopersicum as well.
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•Proteins of the plant Get3a family are localized in the cytoplasm.•A plastidic Get3bc protein exists in all tested plants ranging from moss to Eudicots.•Mitochondrial localized Get3bc proteins exists in A. thaliana but not in tomato or moss.•Plant Get1/Get4 proteins are exclusively localized in the cytoplasm and at the ER.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
Plant genomes encode many lineage-specific, unique transcription factors. Expansion of such gene families has been previously found to coincide with the evolution of morphological ...complexity, although comparative analyses have been hampered by severe sampling bias. Here, we make use of the recently increased availability of plant genomes. We have updated and expanded previous rule sets for domain-based classification of transcription associated proteins (TAPs), comprising transcription factors and transcriptional regulators. The genome-wide annotation of these protein families has been analyzed and made available via the novel TAPscan web interface. We find that many TAP families previously thought to be specific for land plants actually evolved in streptophyte (charophyte) algae; 26 out of 36 TAP family gains are inferred to have occurred in the common ancestor of the Streptophyta (uniting the land plants—Embryophyta—with their closest algal relatives). In contrast, expansions of TAP families were found to occur throughout streptophyte evolution. 17 out of 76 expansion events were found to be common to all land plants and thus probably evolved concomitant with the water-to-land-transition.
Many differentiated plant cells can dedifferentiate into stem cells, reflecting the remarkable developmental plasticity of plants. In the moss Physcomitrella patens, cells at the wound margin of ...detached leaves become reprogrammed into stem cells. Here, we report that two paralogous P. patens WUSCHEL-related homeobox 13-like (PpWOX13L) genes, homologs of stem cell regulators in flowering plants, are transiently upregulated and required for the initiation of cell growth during stem cell formation. Concordantly, Δppwox13l deletion mutants fail to upregulate genes encoding homologs of cell wall loosening factors during this process. During the moss life cycle, most of the Δppwox13l mutant zygotes fail to expand and initiate an apical stem cell to form the embryo. Our data show that PpWOX13L genes are required for the initiation of cell growth specifically during stem cell formation, in analogy to WOX stem cell functions in seed plants, but using a different cellular mechanism.
Summary
In the last few years, next‐generation sequencing techniques have started to be used to identify new viruses infecting plants. This has allowed to rapidly increase our knowledge on viruses ...other than those causing symptoms in economically important crops. Here we used this approach to identify a virus infecting Physcomitrium patens that has the typical structure of the double‐stranded RNA endogenous viruses of the Amalgaviridae family, which we named Physcomitrium patens amalgavirus 1, or PHPAV1. PHPAV1 is present only in certain accessions of P. patens, where its RNA can be detected throughout the cell cycle of the plant. Our analysis demonstrates that PHPAV1 can be vertically transmitted through both paternal and maternal germlines, in crosses between accessions that contain the virus with accessions that do not contain it. This work suggests that PHPAV1 can replicate in genomic backgrounds different from those that actually contain the virus and opens the door for future studies on virus–host coevolution.
Significance Statement
We describe here Physcomitrium patens amalgavirus 1 (PHPAV1), the first virus associated with P. patens. PHPAV1 is a double‐stranded RNA endogenous virus of the Amalgaviridae family present in only certain accessions of P. patens and can be transmitted vertically through both paternal and maternal germlines.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The transition from germinating seeds to emerging seedlings is one of the most vulnerable plant life cycle stages. Heteromorphic diaspores (seed and fruit dispersal units) are an adaptive bet-hedging ...strategy to cope with spatiotemporally variable environments. While the roles and mechanisms of seedling traits have been studied in monomorphic species, which produce one type of diaspore, very little is known about seedlings in heteromorphic species. Using the dimorphic diaspore model
(Brassicaceae), we identified contrasting mechanisms in the germination responses to different temperatures of the mucilaginous seeds (M
seed morphs), the dispersed indehiscent fruits (IND fruit morphs), and the bare non-mucilaginous M
seeds obtained from IND fruits by pericarp (fruit coat) removal. What follows the completion of germination is the pre-emergence seedling growth phase, which we investigated by comparative growth assays of early seedlings derived from the M
seeds, bare M
seeds, and IND fruits. The dimorphic seedlings derived from M
and M
seeds did not differ in their responses to ambient temperature and water potential. The phenotype of seedlings derived from IND fruits differed in that they had bent hypocotyls and their shoot and root growth was slower, but the biomechanical hypocotyl properties of 15-day-old seedlings did not differ between seedlings derived from germinated M
seeds, M
seeds, or IND fruits. Comparison of the transcriptomes of the natural dimorphic diaspores, M
seeds and IND fruits, identified 2,682 differentially expressed genes (DEGs) during late germination. During the subsequent 3 days of seedling pre-emergence growth, the number of DEGs was reduced 10-fold to 277 root DEGs and 16-fold to 164 shoot DEGs. Among the DEGs in early seedlings were hormonal regulators, in particular for auxin, ethylene, and gibberellins. Furthermore, DEGs were identified for water and ion transporters, nitrate transporter and assimilation enzymes, and cell wall remodeling protein genes encoding enzymes targeting xyloglucan and pectin. We conclude that the transcriptomes of seedlings derived from the dimorphic diaspores, M
seeds and IND fruits, undergo transcriptional resetting during the post-germination pre-emergence growth transition phase from germinated diaspores to growing seedlings.
• The Arabidopsis COP1/SPA complex is a key repressor of photomorphogenesis that suppresses light signaling in the dark. Both COP1 and SPA proteins are essential components of this complex. Although ...COP1 also exists in humans, SPA genes are specific to the green lineage.
• To elucidate the evolution of SPA genes we analyzed SPA functions in the moss Physcomitrella patens by characterizing knockout mutants in the two Physcomitrella SPA genes PpSPAa and PpSPAb.
• Light-grown PpspaAB double mutants exhibit smaller gametophores than the wild-type. In the dark, PpspaAB mutant gametophores show enhanced continuation of growth but etiolate normally. Gravitropism in the dark is reduced in PpspaAB mutant protonemata. The expression of light-regulated genes is mostly not constitutive in PpspaAB mutants. PpSPA and PpCOP1 interact; PpCOP1 also interacts with the transcription factor PpHY5 and, indeed, PpHY5 is destabilized in dark-grown Physcomitrella. Degradation of PpHY5 in darkness, however, does not require PpSPAa and PpSPAb.
• The data suggest that COP1/SPA-mediated light signaling is only partially conserved between Arabidopsis and Physcomitrella. Whereas COP1/SPA interaction and HY5 degradation in darkness is conserved, the role of SPA proteins appears to have diverged. PpSPA genes, unlike their Arabidopsis counterparts, are only required to suppress a subset of light responses in darkness.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
• Defects in flagella/cilia are often associated with infertility and disease. Motile male gametes (sperm cells) are an ancestral eukaryotic trait that has been lost in several lineages like ...flowering plants. Here, we made use of a phenotypic male fertility difference between two moss (Physcomitrella patens) ecotypes to explore spermatozoid function.
• We compare genetic and epigenetic variation as well as expression profiles between the Gransden and Reute ecotype to identify a set of candidate genes associated with moss male infertility. We generated a loss-of-function mutant of a coiled-coil domain containing 39 (ccdc39) gene that is part of the flagellar hydin network.
• Defects in mammal and algal homologues of this gene coincide with a loss of fertility, demonstrating the evolutionary conservation of flagellar function related to male fertility across kingdoms. The Ppccdc39 mutant resembles the Gransden phenotype in terms of male fertility.
• Potentially, several somatic (epi-)mutations occurred during prolonged vegetative propagation of Gransden, causing regulatory differences of for example the homeodomain transcription factor BELL1. Probably these somatic changes are causative for the observed male fertility defect. We propose that moss spermatozoids might be employed as an easily accessible system to study male infertility of humans and animals in terms of flagellar structure and movement.
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