RESUMO
PREMISE OF THE STUDY: Polyploidy and reticulate evolution are often a complication for discovering phylogenetic relationships between genera and species. Despite the huge economic importance of sugarcane (Saccharum officinarum-Poaceae, Andropogoneae), the limits of the genus Saccharum and its species are complex and largely unresolved, involving both polyploidy and reticulate evolution. This study aimed to assess the phylogenetic relationships of Saccharum s.l., including Erianthus and Tripidium, as well as investigate the taxonomic circumscription of the South American species of the genus. METHODS: Molecular cloning and sequencing of five regions of four low-copy nuclear loci were performed, including Aberrant panicle organization1 (apo1), Dwarf8 (d8), two exons of Erect panicle2 (ep2-ex7 and ep2-ex8), and Retarded palea1 (rep1). Concatenated trees were reconstructed using Maximum Parsimony, Maximum Likelihood, and Bayesian Inference analyses. KEY RESULTS: The allopolyploid origin of Saccharum was demonstrated using evidence from nuclear genes. The samples of Saccharum s.l. grouped in two distinct clades, with S. arundinaceum and S. ravennae (= Tripidium, or Erianthus sect. Ripidium) apart from all other species analyzed of the genus. Saccharum angustifolium, S. asperum, and S. villosum correspond to distinct clades (different species). The plants with intermediate morphology between S. angustifolium and S. villosum presented a pattern of paralogues consistent with a hybrid origin. CONCLUSIONS: Saccharum s.l. is polyphyletic and Tripidium should be recognized as a distinct genus. However, no strong evidence was found to support the segregation of Erianthus. The taxonomic circumscription of the South American species of the genus was resolved and the occurrence of natural hybrids was documented. Better understanding of the phylogenetic relationships of Saccharum and relatives may be useful for sugarcane breeders to identify potential taxa for interspecific and intergeneric crosses in the genetic improvement of sugarcane.
Assuntos
Evolução Biológica , DNA de Plantas/análise , Genoma de Planta , Fenótipo , Filogenia , Poliploidia , Saccharum/genética , Teorema de Bayes , Classificação , Clonagem Molecular , Éxons , Loci Gênicos , Hibridização Genética , Saccharum/anatomia & histologia , América do Sul , Especificidade da EspécieRESUMO
Included in the PACMAD clade of the family Poaceae (Panicoideae, Arundinoideae, Chloridoideae, Micrairoideae, Aristidoideae, Danthonioideae), the tribe Paniceae s.l. is one of the largest tribes of the subfamily Panicoideae, with more than 2000 species. This tribe comprises a huge morphological, cytological and physiological diversity represented by different inflorescence types, several basic chromosome numbers, and at least four major photosynthetic pathways. The tribe Paniceae has been the subject of molecular studies that have confirmed its paraphyly: two major clades were recognized based on their basic chromosome numbers (x = 9, x = 10). The x = 10 Paniceae clade is sister to the Andropogoneae-Arundinelleae s.s. clade (x = 10), while the combined x = 10 clade is sister to the x = 9 clade that contains the remaining genera of Paniceae. As a result of a recent realignment within the tribe in terms of the phylogenetic position of minor and major Paniceae genera, a reanalysis of the whole sampling is performed and new underrepresented taxa are discussed. A total of 155 genera, currently considered within subfamily Panicoideae, are represented here by almost all genera of Paniceae s.l., representatives of Andropogoneae and Arundinelleae s.s., and the endemic and small tribe Steyermarkochloeae; we also included specimens of subfamily Micrairoideae, tribes Isachneae and Eriachneae. The sampling includes as outgroups 18 genera of the PACMAD clade (excluding Panicoideae) and four genera from the BEP clade (Bambusoideae, Ehrhartoideae, Pooideae), rooting with Bromus inermis. A matrix with 265 taxa based on the combined evidence from ndhF plastid sequences (2074 bp) and 57 morphological characters was subjected to parsimony analyses. Jackknife resampling was used to calculate group support. Most clades are characterized by morphological, cytological, anatomical, and/or physiological characters. Major tribal changes are based on the basic chromosome number; the pantropical x = 9 clade is here recognized as Paniceae s.s., while the American x = 10 Paniceae s.l. is restricted to the reinstated tribe Paspaleae. The optimization of the photosynthetic pathway for the Paspaleae-Andropogoneae-Arundinelleae s.s. clade, including the monotypic Reynaudia, shows a plesiomorphic C4 state while the ancestral state for Paniceae s.s. is ambiguous. If Reynaudia were not included or placed elsewhere, the ancestral photosynthetic pathway for both the Paspaleae-Andropogoneae-Arundinelleae s.s. clade and the Paniceae s.s. would be unambiguously C3 . In order to explore character evolution further, the morphological characters were mapped onto one of the most parsimonious trees. A relationship between photosynthetic pathways and inflorescence morphology is suggested here for the first time. Based on the optimization of morphological characters and additional data, we propose names for almost all inner clades at the rank of subtribe with a few groups as incertae sedis. With this extensive sampling, we resolved the phylogenetic relationships and the assignation of synapomorphies, and improved the support in subtribe sorting; consequently a robust circumscription of the tribe Paniceae s.l. is proposed.
RESUMO
BACKGROUNDS AND AIMS: Twenty-five genera having sterile inflorescence branches were recognized as the bristle clade within the x = 9 Paniceae (Panicoideae). Within the bristle clade, taxonomic circumscription of Cenchrus (20-25 species), Pennisetum (80-140) and the monotypic Odontelytrum is still unclear. Several criteria have been applied to characterize Cenchrus and Pennisetum, but none of these has proved satisfactory as the diagnostic characters, such as fusion of bristles in the inflorescences, show continuous variation. METHODS: A phylogenetic analysis based on morphological, plastid (trnL-F, ndhF) and nuclear (knotted) data is presented for a representative species sampling of the genera. All analyses were conducted under parsimony, using heuristic searches with TBR branch swapping. Branch support was assessed with parsimony jackknifing. KEY RESULTS: Based on plastid and morphological data, Pennisetum, Cenchrus and Odontelytrum were supported as a monophyletic group: the PCO clade. Only one section of Pennisetum (Brevivalvula) was supported as monophyletic. The position of P. lanatum differed among data partitions, although the combined plastid and morphology and nuclear analyses showed this species to be a member of the PCO clade. The basic chromosome number x = 9 was found to be plesiomorphic, and x = 5, 7, 8, 10 and 17 were derived states. The nuclear phylogenetic analysis revealed a reticulate pattern of relationships among Pennisetum and Cenchrus, suggesting that there are at least three different genomes. Because apomixis can be transferred among species through hybridization, its history most likely reflects crossing relationships, rather than multiple independent appearances. CONCLUSIONS: Due to the consistency between the present results and different phylogenetic hypotheses (including morphological, developmental and multilocus approaches), and the high support found for the PCO clade, also including the type species of the three genera, we propose unification of Pennisetum, Cenchrus and Odontelytrum. Species of Pennisetum and Odontelytrum are here transferred into Cenchrus, which has priority. Sixty-six new combinations are made here.
Assuntos
Cenchrus/genética , Pennisetum/genética , Plastídeos/genética , Poaceae/genética , Cenchrus/classificação , Pennisetum/classificação , Ploidias , Poaceae/classificaçãoRESUMO
LEAFY HULL STERILE1 (LHS1) is an MIKC-type MADS-box gene in the SEPALLATA class. Expression patterns of LHS1 homologs vary among species of grasses, and may be involved in determining palea and lemma morphology, specifying the terminal floret of the spikelet, and sex determination. Here we present LHS1 expression data from Eleusine indica (subfamily Chloridoideae) and Megathyrsus maximus (subfamily Panicoideae) to provide further insights into the hypothesized roles of the gene. E. indica has spikelets with three to eight florets that mature acropetally; E. indica LHS1 (EiLHS1) is expressed in the palea and lemma of all florets. In contrast, M. maximus has spikelets with two florets that mature basipetally; M. maximus LHS1 (MmLHS1) is expressed in the palea and lemma of the distal floret only. These data are consistent with the hypothesis that LHS1 plays a role in determining palea and lemma morphology and specifies the terminal floret of basipetally maturing grass spikelets. However, LHS1 expression does not correlate with floret sex expression; MmLHS1 is restricted to the bisexual distal floret, whereas EiLHS1 is expressed in both sterile and bisexual floret meristems. Phylogenetic analyses reconstruct a complex pattern of LHS1 expression evolution in grasses. LHS1 expression within the gynoecium has apparently been lost twice, once before diversification of a major clade within tribe Paniceae, and once in subfamily Chloridoideae. These data suggest that LHS1 has multiple roles during spikelet development and may have played a role in the diversification of spikelet morphology.