Genome assemblies of 11 bamboo species highlight diversification induced by dynamic subgenome dominance.

Polyploidy (genome duplication) is a pivotal force in evolution. However, the interactions between parental genomes in a polyploid nucleus, frequently involving subgenome dominance, are poorly understood. Here we showcase analyses of a bamboo system (Poaceae: Bambusoideae) comprising a series of lineages from diploid (herbaceous) to tetraploid and hexaploid (woody), with 11 chromosome-level de novo genome assemblies and 476 transcriptome samples. We find that woody bamboo subgenomes exhibit stunning karyotype stability, with parallel subgenome dominance in the two tetraploid clades and a gradual shift of dominance in the hexaploid clade. Allopolyploidization and subgenome dominance have shaped the evolution of tree-like lignified culms, rapid growth and synchronous flowering characteristic of woody bamboos as large grasses. Our work provides insights into genome dominance in a remarkable polyploid system, including its dependence on genomic context and its ability to switch which subgenomes are dominant over evolutionary time.

Testing complete plastomes and nuclear ribosomal DNA sequences for species identification in a taxonomically difficult bamboo genus Fargesia.

Fargesia, the largest genus within the temperate bamboo tribe Arundinarieae, has more than 90 species mainly distributed in the mountains of Southwest China. The Fargesia bamboos are important components of the subalpine forest ecosystems that provide food and habitat for many endangered animals, including the giant panda. However, species-level identification of Fargesia is difficult. Moreover, the rapid radiation and slow molecular evolutionary rate of Fargesia pose a significant challenge to using DNA barcoding with standard plant barcodes (rbcL, matK, and ITS) in bamboos. With progress in the sequencing technologies, complete plastid genomes (plastomes) and nuclear ribosomal DNA (nrDNA) sequences have been proposed as organelle barcodes for species identification; however, these have not been tested in bamboos. We collected 196 individuals representing 62 species of Fargesia to comprehensively evaluate the discriminatory power of plastomes and nrDNA sequences compared to standard barcodes. Our analysis indicates that complete plastomes have substantially higher discriminatory power (28.6%) than standard barcodes (5.7%), whereas nrDNA sequences show a moderate improvement (65.4%) compared to ITS (47.2%). We also found that nuclear markers performed better than plastid markers, and ITS alone had higher discriminatory power than complete plastomes. The study also demonstrated that plastomes and nrDNA sequences can contribute to intrageneric phylogenetic resolution in Fargesia. However, neither of these sequences were able to discriminate all the sampled species, and therefore, more nuclear markers need to be identified.

Inflorescences of Fargesiaangustissima T.P. Yi and Yushaniapauciramificans T.P. Yi (Poaceae, Bambusoideae) shed light on the taxonomy of the Sino-Himalayan alpine bamboos.

The taxonomy of the Sino-Himalayan alpine bamboos is controversial due to their complex evolutionary history and further complicated by the scarcity of inflorescence. Here, we supplement the description of the inflorescence of Fargesiaangustissima T.P. Yi and Yushaniapauciramificans T.P. Yi, which shed light on the taxonomy of Fargesia Franchet, Borinda Stapleton and Yushania Keng. F.angustissima has compressed inflorescence unilateral stretching out from reduced spathe, showing a transitional state between species with condensed inflorescence embraced by spathe-like bracts and species with open inflorescence without bracts. Considering that extensive gene flow existed between several clades of Fargesia found in recent studies, a broadly-defined Fargesia s. l. should be adopted. Meanwhile, the inflorescence of Y.pauciramificans has typical characteristics of Yushania, such as axilla with tuberculate glands, rachilla internodes ciliate and cylindrical florets, supporting the delimitation of Yushania.

Two new species of Yushania (Poaceae: Bambusoideae) from South China, with a taxonomic revision of related species.

Two new species of Yushania (Poaceae, Bambusoideae, Arundinarieae) are described and illustrated from Hunan, China. Yushania longshanensis D.Z. Li & X.Y. Ye is distinguished from related species (Y. confusa, Y. angustifolia and Y. pachyclada) by having a thinner culm (0.2-0.3 cm in diameter), glabrous sheath scar, no oral setae, a large glabrous leaf blade (10-20 × 0.9-1.3 cm) and 3-4 pairs of secondary veins. Yushania stoloniforma D.Z. Li & X.Y. Ye has a distinctive scrambling habit, which differs from its putative close allies. Both of these two new species have a solitary branch at the basal nodes and can be assigned to Yushania sect. Yushania based on morphological features. Additionally, we treated Yushania gigantea T.P. Yi & L. Yang as a new synonym of Y. elevata T.P. Yi and renamed Y. microphylla T.P. Yi & L. Yang as Y. weiningensis D.Z. Li & X.Y. Ye.

Parallel ddRAD and Genome Skimming Analyses Reveal a Radiative and Reticulate Evolutionary History of the Temperate Bamboos.

Rapid evolutionary radiations are among the most challenging phylogenetic problems, wherein different types of data (e.g., morphology and molecular) or genetic markers (e.g., nuclear and organelle) often yield inconsistent results. The tribe Arundinarieae, that is, the temperate bamboos, is a clade of tetraploid originated 22 Ma and subsequently radiated in East Asia. Previous studies of Arundinarieae have found conflicting relationships and/or low support. Here, we obtain nuclear markers from ddRAD data for 213 Arundinarieae taxa and parallel sampling of chloroplast genomes from genome skimming for 147 taxa. We first assess the feasibility of using ddRAD-seq data for phylogenetic estimates of paleopolyploid and rapidly radiated lineages, optimize clustering thresholds, and analysis workflow for orthology identification. Reference-based ddRAD data assembly approaches perform well and yield strongly supported relationships that are generally concordant with morphology-based taxonomy. We recover five major lineages, two of which are notable (the pachymorph and leptomorph lineages), in that they correspond with distinct rhizome morphologies. By contrast, the phylogeny from chloroplast genomes differed significantly. Based on multiple lines of evidence, the ddRAD tree is favored as the best species tree estimation for temperate bamboos. Using a time-calibrated ddRAD tree, we find that Arundinarieae diversified rapidly around the mid-Miocene corresponding with intensification of the East Asian monsoon and the evolution of key innovations including the leptomorph rhizomes. Our results provide a highly resolved phylogeny of Arundinarieae, shed new light on the radiation and reticulate evolutionary history of this tribe, and provide an empirical example for the study of recalcitrant plant radiations. [Arundinarieae; ddRAD; paleopolyploid; genome skimming; rapid diversification; incongruence.].

Two new species of Fargesia (Poaceae, Bambusoideae) from southwestern China.

Two new species of Fargesia, one from Xizang (Tibet) and one from Yunnan, China, are described and illustrated. Fargesia viridis D.Z. Li & X.Y. Ye is characterized by its densely white powder, nearly solid internodes, yellow setose sheath scar and culm sheaths, and 4-6 leaves of large size. Fargesia purpurea D.Z. Li & X.Y. Ye has thinner culms (0.5-1.4 cm in diameter), a ring of 4-5 mm tall brown setae below nodes, fewer branches, glabrous sheath scar and culm sheaths, differentiated from the related species.

Yushania tongpeii (Poaceae, Bambusoideae), a new bamboo species from north-eastern Yunnan, China.

Yushania tongpeii D.Z.Li, Y.X.Zhang & E.D.Liu, a new species of the temperate bamboo tribe Arundinarieae (Poaceae: Bambusoideae), is described and illustrated from north-eastern Yunnan, China. Yushania tongpeii is characterised by taller branching from nodes 1-2 m above the ground, usually three branches at the node, sparse purple spots and thin white powder on the internode, densely purple-spotted culm sheaths, glabrous margins of culm sheaths and tomentose leaf ligules. Based on the morphological features, this new species is assigned to section Yushania.

Genome Sequences Provide Insights into the Reticulate Origin and Unique Traits of Woody Bamboos.

Polyploidization is a major driver of speciation and its importance to plant evolution has been well recognized. Bamboos comprise one diploid herbaceous and three polyploid woody lineages, and are members of the only major subfamily in grasses that diversified in forests, with the woody members having a tree-like lignified culm. In this study, we generated four draft genome assemblies of major bamboo lineages with three different ploidy levels (diploid, tetraploid, and hexaploid). We also constructed a high-density genetic linkage map for a hexaploid species of bamboo, and used a linkage-map-based strategy for genome assembly and identification of subgenomes in polyploids. Further phylogenomic analyses using a large dataset of syntenic genes with expected copies based on ploidy levels revealed that woody bamboos originated subsequent to the divergence of the herbaceous bamboo lineage, and experienced complex reticulate evolution through three independent allopolyploid events involving four extinct diploid ancestors. A shared but distinct subgenome was identified in all polyploid forms, and the progenitor of this subgenome could have been critical in ancient polyploidizations and the origin of woody bamboos. Important genetic clues to the unique flowering behavior and woody trait in bamboos were also found. Taken together, our study provides significant insights into ancient reticulate evolution at the subgenome level in the absence of extant donor species, and offers a potential model scenario for broad-scale study of angiosperm origination by allopolyploidization.

New distribution records of two bamboo species in Yunnan, China with description of the inflorescence for Melocalamus yunnanensis (Poaceae, Bambusoideae).

Ampelocalamus actinotrichus (Merrill & Chun) S. L. Chen, T. H. Wen & G. Y. Sheng and Neomicrocalamus prainii (Gamble) P. C. Keng are reported with new distribution records in southern and southeastern Yunnan, China, respectively. Ampelocalamus actinotrichus was previously recorded to be endemic to Hainan, China, and Neomicrocalamus prainii to be distributed in southern Tibet and western Yunnan in China, northeastern India, and Burma. The identities of individuals collected in southern and southeastern Yunnan of these two species are confirmed by molecular evidence. The new distribution record of Ampelocalamus actinotrichus provides a case at the species level for confirming floristic affinities of southern Yunnan and Hainan Island in south China. The disjunct distribution of Neomicrocalamus prainii in Yunnan is concordant with the ecogeographical diagonal line from northwestern Yunnan to southeastern Yunnan and this may imply a tropical origin of this species. In addition, the inflorescence of Melocalamus yunnanensis (T. H. Wen) T. P. Yi is described.