Subunit polypeptide composition of rubisco and the origin of allopolyploid Arabidopsis suecica (Brassicaceae)

The polypeptide composition of the large and small subunits of Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) from Arabidopsis thaliana, A. suecica and Cardaminopsis arenosa have been studied by IEF (isoelectric focusing) analysis. The putative recent alopolyploid origin of A. suecica is supported. The chloroplast encoded large subunits served to identify solely A. thaliana as the maternal parent whereas the nuclear encoded small subunits indicate C. arenosa as the paternal species.     

Genome structure and evolution in the cruciferous tribe Thlaspideae (Brassicaceae)

Whole-genome duplications (WGDs) and chromosome rearrangements (CRs) play the key role in driving the diversification and evolution of plant lineages. Although the direct link between WGDs and plant diversification is well documented, relatively few studies focus on the evolutionary significance of CRs. The cruciferous tribe Thlaspideae represents an ideal model system to address the role of large-scale chromosome alterations in genome evolution, as most Thlaspideae species share the same diploid chromosome number (2n = 2x = 14). Here we constructed the genome structure in 12 Thlaspideae species, including field pennycress (Thlaspi arvense) and garlic mustard (Alliaria petiolata). We detected and precisely characterized genus- and species-specific CRs, mostly pericentric inversions, as the main genome-diversifying drivers in the tribe. We reconstructed the structure of seven chromosomes of an ancestral Thlaspideae genome, identified evolutionary stable chromosomes versus chromosomes prone to CRs, estimated the rate of CRs, and uncovered an allohexaploid origin of garlic mustard from diploid taxa closely related to A. petiolata and Parlatoria cakiloidea. Furthermore, we performed detailed bioinformatic analysis of the Thlaspideae repeatomes, and identified repetitive elements applicable as unique species- and genus-specific barcodes and chromosome landmarks. This study deepens our general understanding of the evolutionary role of CRs, particularly pericentric inversions, in plant genome diversification, and provides a robust base for follow-up whole-genome sequencing efforts.     

Photoinhibition of radish (Raphanus sativus L) seed germination: control of growth potential by cell-wall yielding in the embryo

The biophysical mechanism underlying photoinhibition of radish (Raphanus sativus L.) seed germination was investigated using three cultivars differing in sensitivity to continuous irradiation with far-red light (high-irradiance reaction of phytochrome). Sensitivity of germination to the inhibitory action of light was assessed by probing germination under osmotic stress (incubation in media of low water potentials adjusted with polyethylene glycol 6000) and expressed in terms of ‘germination potential’ (positive value of the water potential at which germination is inhibited by 50%). Far-red light decreases the germination potential to various degrees in the different cultivars, reflecting the light-sensitivity of germination in water. Removal of the seed coat increases the germination potential by a constant amount in darkness and light. It is concluded that germination depends on the expansive force of the embryo which can be drastically diminished by far-red light. Seed-coat constraint and expansive force of the embryo interact additively on the level of the germination potential. Photoinhibition of germination was accompanied by an inhibition of water uptake into the seed. Analysis of seed water relations showed that osmotic pressure and turgor assumed higher levels in photoinhibited seeds, compared to seeds germinating in darkness, while the water potential was close to zero under both conditions. Far-red light produced a shift (to less negative values) in the curve relating water-uptake rate to external water potential, i.e. a reduction in the driving force for water uptake. It is concluded that photoinhibition of germination results from the maintenance of a high threshold of cell-wall extensibility in the embryo.     

Thlaspi s.str. (Brassicaceae) versus Thlaspi s.l.: morphological and anatomical characters in the light of ITS nrDNA sequence data

 Nuclear ribosomal (ITS) DNA sequence data from representatives of eleven out of 12 genera previously included in Thlaspi sensu lato were analyzed to elucidate relationships within the former genus Thlaspi sensu lato. Sequences from Thlaspi segregates Noccaea, Masmenia, Callothlaspi, Kotschyella, Microthlaspi, and Noccidium were added to the existing data sets, and only some Thlaspi sensu lato segregates formed a monophyletic group. The recently renamed genus Pseudosempervivum, formerly part of the genus Cochlearia, has been shown to be closely related to this group as well. Microthlaspi consists of three independent lineages of which Microthlaspi umbellatum is closely related to Neurotropis. The Thlaspi s.str. taxa including the type species T. arvense, are closely related to Peltaria and Alliaria and they represent a monophyletic group. Kotschyella and Noccidium, which were also integrated into Thlaspi s.l. are not closely related to any Thlaspi lineage. Therefore, we suggest major taxonomical changes which are not in agreement with concepts based on morphological data. Our ITS based phylogeny demonstrates that subtribe Thlaspidinae comprises some additional genera such as Teesdalia, Peltaria, and Alliaria, the latter two even previously classified in other tribes than tribe Lepidieae. Received August 15, 2000 Accepted January 30, 2001     

Intercropping oilseed rape as a potential relay crop for enhancing the biological control of green peach aphids and aphid‐transmitted virus diseases

Tobacco viruses transmitted by green peach aphids, Myzus persicae (Sulzer) (Hemiptera: Aphididae), cause severe disease in flue‐cured tobacco, Nicotiana tabacum L. (Solanaceae), in China and throughout the world. Field experiments were conducted in 2016 and 2017 in Longyan City, Fujian Province, China, to determine whether M. persicae and aphid‐transmitted virus diseases are affected by intercropping of oilseed rape, Brassica napus L. (Brassicaceae), in tobacco fields. The results showed that, compared with those in monocultured fields, the densities of M. persicae and winged aphids in intercropped fields significantly decreased in both 2016 and 2017. In particular, the appearance of winged aphids was delayed by ca. 7 days. Moreover, the densities of Aphidius gifuensis Ashmead (Hymenoptera: Aphidiidae), a parasitoid of the aphid, significantly increased in 2016 and 2017. Accordingly, the incidence rates of aphid‐transmitted virus diseases (those caused by the cucumber mosaic virus, potato virus Y, and tobacco etch virus) significantly decreased in the intercropped fields in 2016 and 2017. Tobacco yields and monetary value significantly increased in 2016 (by 10–25 and 14–29%, respectively) and 2017 (by 17–22 and 22–34%, respectively). Consequently, our results suggest that intercropping oilseed rape in tobacco fields is a good approach to regulating and controlling aphids and tobacco mosaic viruses, for example potyvirus, and this intercropping can help control aphid‐transmitted virus diseases in tobacco.     

Progesterone 5β‐reductase genes of the Brassicaceae family as function‐associated molecular markers

This study aimed to define progesterone 5β‐reductases (P5βR, EC 1.3.99.6, enone 1,4‐reductases) as function‐associated molecular markers at the plant family level. Therefore cDNAs were isolated from 25 Brassicaceae species, including two species, Erysimum crepidifolium and Draba aizoides, known to produce cardiac glycosides. The sequences were used in a molecular phylogeny study. The cladogram created is congruent to the existing molecular analyses. Recombinant His‐tagged forms of the P5βR cDNAs from Aethionema grandiflorum, Draba aizoides, Nasturtium officinale, Raphanus sativus and Sisymbrium officinale were expressed in E. coli. Enone 1,4‐reductase activity was demonstrated in vitro using progesterone and 2‐cyclohexen‐1‐one as substrates. Evidence is provided that functional P5βRs are ubiquitous in the Brassicaceae. The recombinant P5βR enzymes showed different substrate preferences towards progesterone and 2‐cyclohexen‐1‐one. Sequence comparison of the catalytic pocket of the P5βR enzymes and homology modelling using Digitalis lanata P5βR (PDB ID: 2V6G) as template highlighted the importance of the hydrophobicity of the binding pocket for substrate discrimination. It is concluded that P5βR genes or P5βR proteins can be used as valuable function‐associated molecular markers to infer taxonomic relationship and evolutionary diversification from a metabolic/catalytic perspective.     

Evolutionary dynamics of retrotransposons following autopolyploidy in the Buckler Mustard species complex

Long terminal repeat retrotransposons (LTR‐RTs) represent a major fraction of plant genomes, but processes leading to transposition bursts remain elusive. Polyploidy expectedly leads to LTR‐RT proliferation, as the merging of divergent diploids provokes a genome shock activating LTR‐RTs and/or genetic redundancy supports the accumulation of active LTR‐RTs through relaxation of selective constraints. Available evidence supports interspecific hybridization as the main trigger of genome dynamics, but few studies have addressed the consequences of intraspecific polyploidy (i.e. autopolyploidy), where the genome shock is expectedly minimized. The dynamics of LTR‐RTs was thus here evaluated through low coverage 454 sequencing of three closely related diploid progenitors and three independent autotetraploids from the young Biscutella laevigata species complex. Genomes from this early diverging Brassicaceae lineage presented a minimum of 40% repeats and a large diversity of transposable elements. Differential abundances and patterns of sequence divergence among genomes for 37 LTR‐RT families revealed contrasted dynamics during species diversification. Quiescent LTR‐RT families with limited genetic variation among genomes were distinguished from active families (37.8%) having proliferated in specific taxa. Specific families proliferated in autopolyploids only, but most transpositionally active families in polyploids were also differentiated among diploids. Low expression levels of transpositionally active LTR‐RT families in autopolyploids further supported that genome shock and redundancy are non‐mutually exclusive triggers of LTR‐RT proliferation. Although reputed stable, autopolyploid genomes show LTR‐RT fractions presenting analogies with polyploids between widely divergent genomes.     

Karyotype evolution in apomictic Boechera and the origin of the aberrant chromosomes

Chromosome rearrangements may result in both decrease and increase of chromosome numbers. Here we have used comparative chromosome painting (CCP) to reconstruct the pathways of descending and ascending dysploidy in the genus Boechera (tribe Boechereae, Brassicaceae). We describe the origin and structure of three Boechera genomes and establish the origin of the previously described aberrant Het and Del chromosomes found in Boechera apomicts with euploid (2n = 14) and aneuploid (2n = 15) chromosome number. CCP analysis allowed us to reconstruct the origin of seven chromosomes in sexual B. stricta and apomictic B. divaricarpa from the ancestral karyotype (n = 8) of Brassicaceae lineage I. Whereas three chromosomes (BS4, BS6, and BS7) retained their ancestral structure, five chromosomes were reshuffled by reciprocal translocations to form chromosomes BS1‐BS3 and BS5. The reduction of the chromosome number (from x = 8 to x = 7) was accomplished through the inactivation of a paleocentromere on chromosome BS5. In apomictic 2n = 14 plants, CCP identifies the largely heterochromatic chromosome (Het) being one of the BS1 homologues with the expansion of pericentromeric heterochromatin. In apomictic B. polyantha (2n = 15), the Het has undergone a centric fission resulting in two smaller chromosomes – the submetacentric Het′ and telocentric Del. Here we show that new chromosomes can be formed by a centric fission and can be fixed in populations due to the apomictic mode of reproduction.     

Acylated anthocyanins in flowers of Moricandia DC. (Brassicaceae)

New anthocyanin (MAA-3) in the flowers of Moricandia arvensis.

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Isolation of microsatellite markers for Contarinia nasturtii,a European pest invading the New World

Microsatellite markers were developed for epidemiological studies on Contarinia nasturtii (Diptera, Cecidomyiidae), a native European pest that was introduced to the New World in 1996. Nine loci were found to be polymorphic and suitable for the analysis of 56 male individuals that were collected using pheromone traps. These markers all conform to Hardy–Weinberg expectations in at least one of the two tested populations, and carry an average number of 11 alleles among populations and observed levels of heterozygosity ranging from 0.32 to 0.86. Primers for all markers also successfully amplified fragments from Contarinia pisi and Contarinia tritici.