Information on the amount of genetic diversity in switchgrass (Panicum virgatum L.) is necessary to enhance the effectiveness of breeding programs and germplasm conservation efforts. This study characterized and assessed genetic diversity by means of RAPD markers among 14 populations representing upland and lowland switchgrass ecotypes. Forty-five of 128 primers produced polymorphic markers among sets of genomic DNA pooled from individual genotypes of each population. Five primers were selected to amplify a total of 91 polymorphic loci among genotypes. The RAPD markers were scored for presence or absence of bands to generate distance matrices for cluster analysis. Overall similarity was 65% among populations compared to 81% within populations. Blackwell and Caddo were the most similar populations (78%) based on RAPD markers, whereas Alamo and Forestburg were the most divergent (53%). Cluster analysis clearly segregated populations into two main groups (putatively based on ecotype) and united individual genotypes within a population into discrete groups within the larger clusters. Although the relationship between ploidy level and ecotype remained unclear, RAPD profiles can be used to identify switchgrass populations and may be useful in predicting relationships between experimental germplasm sources and released populations. S WITCHGRASS is a highly outcrossing, perennial warmseason grass which is propagated through seed dispersal and rhizome establishment (Weaver and Fitzpatrick, 1932). It is a widespread component of native North American tall grass prairie with a range of adaptation from Nova Scotia, Ontario, and Maine to North Dakota and Wyoming, south to Florida, Nevada, and Arizona into Mexico and Central America (Hitchcock, 1971). Across this range, switchgrass populations exist either as upland or lowland ecotypes that differ in habitat preference, morphology, and, to some extent, ploidy level (Archer and Bunch, 1953; Porter, 1966). The base chromosome number of switchgrass is n = 9, and lowland ecotypes are believed to be predominantly tetraploid (2n-4x = 36), whereas upland types are presumed hexaploid (2n = 6x = 54) or octoploid (2n = 8x = (Church, 1940; Burton, 1942; Nielson, 1944). Current studies using flow cytometry differ in assessment of switchgrass ploidy levels (Lu et al., 1995; Wullschleger et al. 1996), and octoploid chromosome sets have been reported in populations previously thought to be hexaploid (Taliaferro and Hopkins, 1994). Porter (1966) studied upland and lowland populations of switchgrass under various environmental conditions to determine whether any consistent pattern of morphological variability was associated with ecotype, and if such variation was associated with genetic, environmental, or genetic by environmental influences. Although some modifications of phenotypic expression were observed in greenhouse experiments, the ecotypes exhibited

Peatlands are crucial sinks for atmospheric carbon but are critically threatened due to warming climates. Sphagnum (peat moss) species are keystone members of peatland communities where they actively engineer hyperacidic conditions, which improves their competitive advantage and accelerates ecosystem-level carbon sequestration. To dissect the molecular and physiological sources of this unique biology, we generated chromosome-scale genomes of two Sphagnum species: S. divinum and S. angustifolium. Sphagnum genomes show no gene colinearity with any other reference genome to date, demonstrating that Sphagnum represents an unsampled lineage of land plant evolution. The genomes also revealed an average recombination rate an order of magnitude higher than vascular land plants and short putative U/V sex chromosomes. These newly described sex chromosomes interact with autosomal loci that significantly impact growth across diverse pH conditions. This discovery demonstrates that the ability of Sphagnum to sequester carbon in acidic peat bogs is mediated by interactions between sex, autosomes and environment.

BackgroundPlant secondary cell wall is a renewable feedstock for biofuels and biomaterials production. Arabidopsis VASCULAR-RELATED NAC DOMAIN (VND) has been demonstrated to be a key transcription factor regulating secondary cell wall biosynthesis. However, less is known about its role in the woody species.ResultsHere we report the functional characterization of Populus deltoides WOOD-ASSOCIATED NAC DOMAIN protein 3 (PdWND3A), a sequence homolog of Arabidopsis VND4 and VND5 that are members of transcription factor networks regulating secondary cell wall biosynthesis. PdWND3A was expressed at higher level in the xylem than in other tissues. The stem tissues of transgenic P. deltoides overexpressing PdWND3A (OXPdWND3A) contained more vessel cells than that of wild-type plants. Furthermore, lignin content and lignin monomer syringyl and guaiacyl (S/G) ratio were higher in OXPdWND3A transgenic plants than in wild-type plants. Consistent with these observations, the expression of FERULATE 5-HYDROXYLASE1 (F5H1), encoding an enzyme involved in the biosynthesis of sinapyl alcohol (S unit monolignol), was elevated in OXPdWND3A transgenic plants. Saccharification analysis indicated that the rate of sugar release was reduced in the transgenic plants. In addition, OXPdWND3A transgenic plants produced lower amounts of biomass than wild-type plants.ConclusionsPdWND3A affects lignin biosynthesis and composition and negatively impacts sugar release and biomass production.

Summary Prefoldin (PFD) is a group II chaperonin that is ubiquitously present in the eukaryotic kingdom. Six subunits (PFD1‐6) form a jellyfish‐like heterohexameric PFD complex and function in protein folding and cytoskeleton organization. However, little is known about its function in plant cell wall‐related processes. Here, we report the functional characterization of a PFD gene from Populus deltoides, designated as PdPFD2.2. There are two copies of PFD2 in Populus, and PdPFD2.2 was ubiquitously expressed with high transcript abundance in the cambial region. PdPFD2.2 can physically interact with DELLA protein RGA1_8g, and its subcellular localization is affected by the interaction. In P. deltoides transgenic plants overexpressing PdPFD2.2, the lignin syringyl/guaiacyl ratio was increased, but cellulose content and crystallinity index were unchanged. In addition, the total released sugar (glucose and xylose) amounts were increased by 7.6% and 6.1%, respectively, in two transgenic lines. Transcriptomic and metabolomic analyses revealed that secondary metabolic pathways, including lignin and flavonoid biosynthesis, were affected by overexpressing PdPFD2.2. A total of eight hub transcription factors (TFs) were identified based on TF binding sites of differentially expressed genes in Populus transgenic plants overexpressing PdPFD2.2. In addition, several known cell wall‐related TFs, such as MYB3, MYB4, MYB7, TT8 and XND1, were affected by overexpression of PdPFD2.2. These results suggest that overexpression of PdPFD2.2 can reduce biomass recalcitrance and PdPFD2.2 is a promising target for genetic engineering to improve feedstock characteristics to enhance biofuel conversion and reduce the cost of lignocellulosic biofuel production.

The importance to in vivo translation of sequences immediately upstream of the Drosophila alcohol dehydrogenase (Adh) start codon was examined at two developmental stages. Mutations were introduced into the Adh gene in vitro, and the mutant gene was inserted into the genome via germ line transformation. An A-to-T substitution at the -3 position did not affect relative translation rates of the ADH protein at the second-instar larval stage but resulted in a 2.4-fold drop in translation of ADH at the adult stage. A second mutant gene, containing five mutations in the region -1 to -9, was designed to completely block translation initiation. However, transformant lines bearing these mutations still exhibit detectable ADH, albeit at substantially reduced levels. The average fold reduction at the second-instar larval stage was 5.9, while at the adult stage a 12.5-fold reduction was observed.