A haplotype-resolved genome assembly of Rhododendron vialii based on PacBio HiFi reads and Hi-C data.

Rhododendron vialii (subgen. Azaleastrum) is an evergreen shrub with high ornamental value. This species has been listed as a plant species with extremely small populations (PSESP) for urgent protection by China's Yunnan provincial government in 2021, due to anthropogenic habitat fragmentation. However, limited genomic resources hinder scientifically understanding of genetic threats that the species is currently facing. In this study, we assembled a high-quality haplotype-resolved genome of R. vialii based on PacBio HiFi long reads and Hi-C reads. The assembly contains two haploid genomes with sizes 532.73 Mb and 521.98 Mb, with contig N50 length of 35.67 Mb and 34.70 Mb, respectively. About 99.92% of the assembled sequences could be anchored to 26 pseudochromosomes, and 14 gapless assembled chromosomes were included in this assembly. Additionally, 60,926 protein-coding genes were identified, of which 93.82% were functionally annotated. This is the first reported genome of R. vialii, and hopefully it will lay the foundations for further research into the conservation genomics and horticultural domestication of this ornamentally important species.

Does the critically endangered Rhododendron amesiae deserve top priority for conservation?

1.If a threatened plant has the problem of inaccurate species delimitation, its conservation programs that have previously been implemented might be debated.2.We made a comprehensive comparison of the critically endangered R. amesiae and its close relative R. concinnum, employing both morphological and population genomic data (ddRAD-seq).3.We suggest that the critically endangered R. amesiae can be merged into R. concinnum. Hence, the threatened status of R. amesiae is needed to be reevaluated.

Unusual patterns of hybridization involving two alpine Salvia species: Absence of both F1 and backcrossed hybrids.

Natural hybridization plays an important role in speciation; however, we still know little about the mechanisms underlying the early stages of hybrid speciation. Hybrid zones are commonly dominated by F1s, or backcrosses, which impedes further speciation. In the present study, morphological traits and double digest restriction-site associated DNA sequencing (ddRAD-seq) data have been used to confirm natural hybridization between Salvia flava and S. castanea, the first case of identification of natural hybridization using combined phenotypic and molecular evidence in the East Asian clade of Salvia. We further examined several reproductive barriers in both pre-zygotic and post-zygotic reproductive stages to clarify the causes and consequences of the hybridization pattern. Our results revealed that reproductive isolation between the two species was strong despite the occurrence of hybridization. Interestingly, we found that most of the hybrids were likely to be F2s. This is a very unusual pattern of hybridization, and has rarely been reported before. The prevalence of geitonogamy within these self-compatible hybrids due to short distance foraging by pollinators might explain the origin of this unusual pattern. F2s can self-breed and develop further, therefore, we might be witnessing the early stages of hybrid speciation. Our study provides a new case for understanding the diversification of plants on the Qinghai-Tibet Plateau.

Rhododendron kuomeianum (Ericaceae), a new species from northeastern Yunnan (China), based on morphological and genomic data.

Rhododendron kuomeianum Y.H. Chang, J. Nielsen & Y.P. Ma, a new species of Rhododendron (Ericaceae) within subsect. Maddenia in sect. Rhododendron from Yiliang County, NE Yunnan, China, is described and illustrated. The new species is similar to R. valentinianum, but it can be easily distinguished by its sparse scales on the abaxial surface of the leaf blade, fewer flowers per inflorescence and white corolla with pale red margins. There are also differences in the widths of calyx lobes, leaf blade shape and indumentum characteristics of the petiole between the new species and Rhododendron linearilobum. We confirmed that R. kuomeianum is a new species closely related to R. valentinianum and R. changii with phylogenomic studies of 10 species within this subsection based on restriction site-associated DNA sequencing (RAD-seq) data. These phylogenomic analyses also clarified additional taxonomic problems in this subsection previously raised by morphological analysis. Our findings make a strong case for using next-generation sequencing to explore phylogenetic relationships and identify new species, especially in plants groups with complicated taxonomic problems.

Occurrence and Prevention of Delayed Autonomous Selfing in Salvia umbratica (Lamiaceae).

Delayed autonomous selfing (DAS) provides reproductive assurance under conditions of pollinator and/or pollen-limitation. Few plant species have been investigated to determine if DAS is terminated when a flower is sufficiently pollinated by a pollen vector, thereby saving plant resources for other purposes. We examined this possibility in bumblebee-pollinated Salvia umbratica. We first showed that DAS resulting in high fruit set (100%) and seed set (>80%) per flower occurred in the absence of insect pollinators by means of style recurvature and was completed in 94% of flowers 72 h after they opened. In contrast, in flowers pollinated immediately after opening, DAS was prevented by corollas dropping away before styles recurve toward the upper thecae. We next showed that hand-pollination of flowers immediately after they opened resulted in high fruit set (100%) and seed set (>80%) when 5-10 pollen grains or more were deposited on their stigmas, whereas fruit set and seed set were reduced to 45.00 and 22.50%, respectively, when pollen loads were reduced to 1-3 pollen grains. Finally, we showed that on average single pollinator visits deposited 26 pollen grains on stigmas of flowers that had just opened, which is more than enough to ensure high fruit and seed set. Our results indicate that flower longevity is highly correlated with the pollinator environment and female fitness of S. umbratica, with extended flower longevity allowing DAS to occur being advantageous when pollinators are absent, while reduced floral longevity and prevention of DAS being favored when flowers are pollinated by pollinators. Thus, flower longevity in S. umbratica varies so as to optimize reproductive output and resource efforts, and is dependent on the availability and effectiveness of pollinators to pollinate flowers.