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The Complete Chloroplast Genome and the Phylogenetic Analysis of Panicum bisulcatum (Thumb.) (Poaceae).

The chloroplast (cp) genome of Panicum bisulcatum (Thumb.), a significant agricultural weed, was sequenced and characterized to elucidate its genomic architecture, evolutionary dynamics, and phylogenetic relationships. The complete cp genome was assembled as a circular DNA molecule of 138,489 bp, exhibiting a typical quadripartite structure comprising a large single-copy (LSC, 82,260 bp), a small single-copy (SSC, 12,569 bp), and a pair of inverted repeats (IR, 21,830 bp each) regions. It encodes 135 genes, including 89 protein-coding genes, 49 tRNAs, and 8 rRNAs. Functional annotation revealed that most genes are involved in photosynthesis and genetic system. A total of 51 simple sequence repeats (SSRs) and 62 long repeats (LRs) were identified, providing potential molecular markers. Comparative analysis of IR boundaries highlighted both conserved features and species-specific expansion/contraction events among Panicum species. Phylogenomic analysis robustly placed P. bisulcatum within the genus Panicum, showing a closest relationship with P. incomtum and confirming the monophyly of the genus. Furthermore, single nucleotide polymorphism (SNP) analysis with its closest relative, P. incomtum, revealed 4659 SNPs, with a dominance of synonymous substitutions, indicating the action of purifying selection. This study provides the first comprehensive cp genomic resource for P. bisulcatum, which will facilitate future studies in species identification, phylogenetic reconstruction, population genetics, and the development of sustainable management strategies for this weed.

Phylogeny

Photosynthetic carbon metabolism in Panicum milioides, a C3-C4 intermediate species: evidence for a limited C4 dicarboxylic acid pathway of photosynthesis.

Panicum milioides, a naturally occurring species with C4-like Kranz leaf anatomy, is intermediate between C3 and C4 plants with respect to photo-respiration and the associated oxygen inhibition of photosynthesis. This paper presents direct evidence for a limited degree of C4 photosynthesis in this C3-C4 intermediate species based on: (a) the appearance of 24% of the total 14C fixed following 4 s photosynthesis in 14CO2-air by excised leaves in malate and aspartate and the complete transfer of label from the C4 acids to Calvin cycle intermediates within a 15 s chase in 12CO2-air; (b) pyruvate- or alanine-enhanced light-dependent CO2 fixation and pyruvate stimulation ote- or alanine-enhanced light-dependent CO2 fixation and pyruvate stimulation of oxaloacetate- or 3-phosphoglycerate-dependent O2 evolution by illuminated mesophyll protoplasts, but not bundle sheath strands; and (c) NAD-malic enzyme-dependent decarboxylation of C4 acids at the C-4 carboxyl position, C4 acid-dependent O2 evolution, and 14CO2 donation from (4-14C)C4 acids to Calvin cycle intermediates during photosynthesis by bundle sheath strands, but not mesophyll protoplasts. However, P. milloides differs from C4 plants in that the activity of the C4 cycle enzymes is only 15 to 30% of a C4 Panicum species and the Calvin cycle and phosphoenolpyruvate carboxylase are present in both cell types. From these and related studies (Rathnam, C.K.M. and Chollet, R. (1979) Arch. Biochem. Biophys. 193, 346-354; (1978) Biochem. Biophys. Res. Commun. 85, 801-808) we conclude that reduced photorespiration in P. milioides is due to a limited degree of NAD-malic enzyme-type C4 photosynthesis permitting an increase in pCO2 at the site of bundle sheath, but not mesophyll, ribulose-bisphosphate carboxylase-oxygenase.

Aspartic Acid

Molecular cloning of an alanine aminotransferase from NAD-malic enzyme type C4 plant Panicum miliaceum.

We have determined the nucleotide sequence of a cDNA encoding AlaAT-2, which is believed to function in the C4-pathway of Panicum miliaceum. An open reading frame (1446 bp) encodes a protein of 482 amino acid residues. The deduced amino acid sequence of AlaAT-2 shows 44.2 and 44.8% homology with the amino acid sequences of AlaATs from rat and human livers, respectively. Northern blot analysis showed that the gene encoding AlaAT-2 in mesophyll and bundle sheath cells was the same and transcribed similarly in the cells. The level of translatable mRNA for AlaAT-2 increased dramatically during greening.

Alanine Transaminase

Purification and characterization of alanine aminotransferase from Panicum miliaceum leaves.

Three alanine aminotransferases, two minor (AlaAT-1, AlaAT-3) and one major (AlaAT-2), were detected by native gel electrophoresis of leaf extracts from Panicum miliaceum L. AlaAT-2 was purified to homogeneity and a specific polyclonal antibody was raised against it which did not react with the other two forms of the enzyme. The enzyme, with an apparent molecular size of 102 kDa, appeared to be a dimer of a single 50-kDa polypeptide. The enzyme has a relatively broad pH optima with similar curves for the forward and reverse directions, ranging between 6.5 and 7.5. The Km values of this enzyme were 6.67, 0.15, 5.00, and 0.33 mM for alanine, 2-oxoglutarate, glutamate, and pyruvate, respectively. The activity of AlaAT-2 was found to increase markedly during leaf greening in parallel with the increase of immunochemically titrated protein, and it is suggested to function in the C4 photosynthetic cycle.

Alanine Transaminase

The nucleotide sequence of an infectious insect-transmissible clone of the geminivirus Panicum streak virus.

The infectious genome of a Kenyan isolate of Panicum streak virus (PSV) has been cloned and sequenced. Infection of host plants was done using an Agrobacterium binary vector containing a partial repeat of the genome. Progeny virus from resultant infections proved to be transmissible by the leafhopper Cicadulina mbila (Naude). Comparisons of the amino acid sequences of PSV DNA-encoded proteins with those of previously characterized geminiviruses infecting monocotyledonous plants, including maize streak virus, revealed high levels of identity. The evolutionary relationship between PSV and other geminiviruses infecting monocotyledons is discussed.

Amino Acid Sequence

Genetic modification of the shikimate pathway to reduce lignin content in switchgrass (Panicum virgatum L.) significantly impacts plant microbiomes.

UNLABELLED: Switchgrass (Panicum virgatum L.) is considered a sustainable biofuel feedstock, given its fast-impact growth, low input requirements, and high biomass yields. Improvements in bioenergy conversion efficiency of switchgrass could be made by reducing its lignin content. Engineered switchgrass that expresses a bacterial 3-dehydroshikimate dehydratase (QsuB) has reduced lignin content and improved biomass saccharification due to the rerouting of the shikimate pathway towards the simple aromatic protocatechuate at the expense of lignin biosynthesis. However, the impacts of this QsuB trait on switchgrass microbiome structure and function remain unclear. To address this, wild-type and QsuB-engineered switchgrass were grown in switchgrass field soils, and samples were collected from inflorescences, leaves, roots, rhizospheres, and bulk soils for microbiome analysis. We investigated how QsuB expression influenced switchgrass-associated fungal and bacterial communities using high-throughput Illumina MiSeq amplicon sequencing of ITS and 16S rDNA. Compared to wild-type, QsuB-engineered switchgrass hosted different microbial communities in roots, rhizosphere, and leaves. Specifically, QsuB-engineered plants had a lower relative abundance of arbuscular mycorrhizal fungi (AMF). Additionally, QsuB-engineered plants had fewer Actinobacteriota in root and rhizosphere samples. These findings may indicate that changes in the plant metabolism impact both AMF and Actinobacteriota similarly or potential interactions between AMF and the bacterial community. This study enhances understanding of plant-microbiome interactions by providing baseline microbial data for developing beneficial bioengineering strategies and by assessing nontarget impacts of engineered plant traits on the plant microbiome. IMPORTANCE: Bioenergy crops provide an important strategy for mitigating climate change. Reducing the lignin in bioenergy crops could improve fermentable sugar yields for more efficient conversion into bioenergy and bioproducts. In this study, we assessed how switchgrass engineered for low lignin impacted aboveground and belowground switchgrass microbiome. Our results show unexpected reductions in mycorrhizas and actinobacteria in belowground tissues, raising questions on the resilience and function of genetically engineered plants in agricultural systems.

Panicum

Cloning and sequence analysis of cDNA encoding aspartate aminotransferase isozymes from Panicum miliaceum L., a C4 plant.

The cytosolic and mitochondrial isozymes of aspartate aminotransferase (AspAT) function in the C4 dicarboxylate cycle of photosynthesis. We constructed a cDNA library from leaf tissues of Panicum miliaceum, an NAD-malic-enzyme-type C4 plant and screened the library for AspAT isozymes. A full-length cDNA clone for cytosolic AspAT was isolated. This clone contains an open reading frame that encodes 409 amino acids. We also isolated two cDNA clones for different precursors of mitochondrial AspAT. Comparing these two sequences in the coding regions, we found 12 amino acid substitutions out of 28 base substitutions. The encoded amino acid sequences predict that mitochondrial AspAT are synthesized as precursor proteins of 428 amino acid residues, which each consist of a mature enzyme of 400 amino acid residues and a 28-amino-acid presequence. This prediction coincides with the observation that the in vitro translation product of the mRNA for mitochondrial AspAT was substantially larger than the mature form. A comparison of the amino acid sequences of the AspAT isozymes from P. miliaceum with the published sequences for the enzymes from various animals and microorganisms reveals that functionally and/or structurally important residues are almost entirely conserved in all AspAT species.

Amino Acid Sequence

Nutrient composition and protein quality of minor millets.

Nutrient composition of five minor millets produced and consumed in dry land regions and tribal areas of Andhra Pradesh, India, was evaluated. The millets analysed were Italian millet (Setaria Italica), French millet (Panicum miliaceum), Barnyard millet (Echinachloa colona), Kodo millet (Paspalum scrobiculatum) and little millet (Panicum miliare). The nutrients analysed were proximate principles, amino acids, fibre components, calcium, Phosphorus and Iron. Protein and energy were evaluated by true digestability (TD), biological value (BV), net protein utilization (NPU) and digestible energy (DE) in rats. The protein content was higher and lysine content lower, when compared to major millets. Dehusked millets had lower total dietary fibre (TDF) and tannin. The TD of protein ranged between 95.0 to 99.3, whereas the BV was between 48.3 and 56.5. All the millets were poor sources of calcium, phosphorus and iron, with the exception of french millet.

Calcium

Effect of heating and fortification with lysine on protein quality of minor millets.

The effect of heating and fortification with lysine on the protein quality of five minor millets namely Italian millet (S. Italica), French millet (Panicum miliaceum), Barnyard millet (Echinochloa colona), Kodo millet (Paspalum scrobiculatum) and Little millet (Panicum miliare) was carried out. The N content of the millets ranged from 1.69 to 2.76 per cent. Proximate composition and dietary fibre was estimated. A reduction of 19-25 in TD and increase of 4-18 in BV was observed on auto-claving and both the differences were significant (P less than 0.05) in all millets. However, heat processing did not have a pronounced effect on DE. Fortification with lysine at 0.6 g/100 DM increased both the BV and NPU. Although both heat processing and lysine fortification improved protein utilisation, the effect of fortification was comparatively more than heating.

Amino Acids

Genome typing of southern African subgroup 1 geminiviruses.

The relatedness of subgroup 1 geminiviruses from a variety of naturally infected southern African graminaceous hosts was compared by DNA cross-hybridization, restriction endonuclease mapping and partial sequencing. Cross-hybridization divided the viruses into three groups: those closely related to maize streak virus (MSVs), and separate groups comprising a Panicum sp. virus (PanSV) and two sugarcane viruses (SSVs). Restriction mapping and comparisons, and phylogeny reconstructions from map data, showed that mapped and sequenced maize viruses were all highly similar; that two viruses of grasses and wheat bore limited resemblance to each other and to MSV, and that a mapped local and a sequenced Kenyan PanSV were similar, but that these and the two SSVs were dissimilar to each other and to all other subgroup 1 geminiviruses. The conclusions were: that maize viruses and the two viruses of wheat and grasses are probably strains of MSV; that two SSVs are only distantly related and distinct from MSVs; that the PanSVs are closely related to one another, but also distinct from other viruses; that all of the viruses in this study are part of a 'MSV-related sub-subgroup' of geminiviruses. Partial sequencing of cloned genomes reinforced conclusions drawn from other data, and indicated a definite relationship between the mapped and sequenced Panicum viruses. The implications of the results for taxonomic and epidemiological purposes are discussed.

Africa