High-quality evergreen azalea genome reveals tandem duplication-facilitated low-altitude adaptability and floral scent evolution
High-quality evergreen azalea genome reveals tandem duplication-facilitated low-altitude adaptability and floral scent evolution
Characteristics of Rhododendron ovatum and its genome assembly. (a) Low-altitude and evergreen characteristics of R. ovatum. The genus Rhododendron contains five main subgenera, of which two subgenera (Rhododendron and Hymenanthes) commonly called ‘rhododendron’ are mainly distributed in alpine and subalpine zone, and the other three (Azaleastrum, Tsutsusi, and Pentanthera) commonly called ‘azalea’ are distributed in mountain and hill zone. The subgenera of Rhododendron, Hymenanthes, and Azaleastrum are mostly evergreens, while Tsutsusi are mainly semi-evergreens and Pentanthera are deciduous. Genome sequences of R. delavayi and R. williamsianum in subgenus Hymenanthes, and R. simsii in subgenus Tsutsusi were previously reported (Soza et al., 2019; Yang et al., 2020; Zhang et al., 2017a). (b) Overview of the R. ovatum genome assembly. (i) The 13 pseudochromosomes, (ii) gene density, (iii) transposon elements, (iv) tandem repeats, and (v) collinear blocks of the R. ovatum genome.
Phylogenetic relationship and comparative genomics analyses. (a) Phylogenetic tree based on single-copy genes from 8 plant species in the Ericales, and tomato (S. lycopers) was used as the outgroup. The numbers in purple beside each node shows the estimated divergent time of each node (myr), and those in brackets are 95% confidence intervals for the time of divergence between different clades. The pie diagram on each branch of the tree represents the proportion of orthogroups undergoing gain (orange) or loss (blue) events, and the numbers beside the pie diagram denote the total number of expansion and contraction orthogroups. The numbers under each branch indicate evolutionary distance that represent genetic variance. (b) Gene expansions in R. ovatum compared to R. delavayi and R. williamsianum. Left panel shows enriched GO terms of expansive genes related to stress responses. Bottom and up panels show the names and gene numbers of the expansive gene families involved in the GO terms. The dots indicate corresponding relations between GO terms and gene families. The full names of gene families are listed in Data S3. (c) The phylogenetic tree of NAC genes from R. ovatum and representative plants showing the extremely expanded clade of ANAC001 in R. ovatum. Branches are colour-coded according to species. Asterisks (*) indicate the genes that have undergone positive selection (Ka/Ks > 1). Right penal shows dense tandem arrays of ANAC001 members that are distributed on chromosomes 7 and 12 of R. ovatum. (d) Co-expression network analysis based on a highly expressed NAC gene member (Ro_40853). Orange circles represent transcription factors and blue circles represent structural proteins.
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