Deep genome skimming reveals the hybrid origin of Pseudosasa gracilis (Poaceae: Bambusoideae).

Pseudosasa gracilis (Poaceae: Bambusoideae) is a temperate woody bamboo species endemic to South-central China with a narrow distribution. Previous phylogenetic studies revealed an unexpected, isolated phylogenetic position of Ps. gracilis. Here we conducted phylogenomic analysis by sampling populations of Ps. gracilis and its sympatric species Ps. nanunica and Sinosasa polytricha reflecting different genomic signals, by deep genome skimming. Integrating molecular evidence from chloroplast genes and genome-wide SNPs, we deciphered the phylogenetic relationships of Ps. gracilis. Both plastid and nuclear data indicate that Ps. gracilis is more closely related to Sinosasa, which is discordant with the taxonomic treatment. To further explore this molecular-morphological conflict, we screened 411 "perfect-copy" syntenic genes to reconstruct phylogenies using both the concatenation and coalescent methods. We observed extensive discordance between gene trees and the putative species tree. A significant hybridization event was detected based on 411 genes from the D subgenome, showing Ps. gracilis was a hybrid descendant between Sinosasa longiligulata and Ps. nanunica, with 63.56% and 36.44% inheritance probabilities of each parent. Moreover, introgression events were detected in the C subgenome between Ps. gracilis and S. polytricha in the same distribution region. Our findings suggest that sympatric hybridization and introgression play a crucial role in the origin of Ps. gracilis. By providing an empirical example of bamboo of hybrid origin using comprehensive analyses based on genomic data from different inheritance systems and morphological characters, our study represents a step forward in understanding of reticulate evolution of bamboos.

The identity of Sasaoblongula C.H.Hu (Poaceae, Bambusoideae, Arundinarieae): evidence from morphology and molecular data.

Sasaoblongula was described in 1987 based on a cultivated plant at the bamboo garden of Sun Yat-sen University. This species has two or three branches at the upper nodes, which differ from the rest of Sasa species that have a single branch per node. During the field trip to Baishi Town, Yunfu City, Guangdong Province in July 2021, one bamboo species with oblong foliage leaves was collected and matches the isotype. Then, our question was to test the identity of S.oblongula concerning other Sasa species based on morphology and molecular data. To do that, we sequenced the whole chloroplast genome of S.oblongula and did a phylogenetic analysis. Our morphological results indicate that the new collection is S.oblongula. The phylogenetic tree showed that S.oblongula is close to Pseudosasa, instead of Sasa species. Therefore, we transferred it to the genus Pseudosasa, and a revised description of P.oblongula is provided here.

The complete chloroplast genome of Pseudosasa usawae (Poaceae: Bambusoideae: Arundinarieae) in Taiwan.

Pseudosasa usawae is an endemic species in Taiwan, and grows at an altitude of 600-1200 m. In this study, we fully characterized the complete chloroplast genome of P. usawae. The complete chloroplast sequence was 139,660 bp, including large single-copy (LSC), small single-copy (SSC), and a pair of invert repeats (IR) region of 83,271, 12,803, and 21,793 bp. Besides, the plastid genome comprised a total of 129 genes, including protein-coding, tRNA, and rRNA genes as 83, 38, and 8 genes. Phylogenetic analysis reveals that P. usawae is closely associated with Phyllostachys genus clade, sister to the lineage of Phyllostachys.