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.

Single-base methylome analysis reveals dynamic changes of genome-wide DNA methylation associated with rapid stem growth of woody bamboos.

MAIN CONCLUSION: CG and CHG methylation levels in the rapid shoot growth stages (ST2-ST4) of woody bamboos were obviously decreased, which might regulate the internode elongation during rapid shoot growth, while CHH methylation was strongly associated with shoot developmental time or age. DNA methylation plays a critical role in the regulation of plant growth and development. Woody bamboos have a unique trait of rapid stem growth resulted from internode elongation at the shooting period. However, it is still unclear whether DNA methylation significantly controls the bamboo rapid stem growth. Here we present whole-genome DNA methylation profiles of the paleotropical woody bamboo Bonia amplexicaulis at five newly defined stages of shoot growth, named ST1-ST5. We found that CG and CHG methylation levels in the rapid shoot growth stages (ST2-ST4) were significantly lower than in the incubation (ST1) and plateau stages (ST5). The changes in methylation levels mainly occurred in flanking regions of genes and gene body regions, and 23647 differentially methylated regions (DMRs) were identified between ST1 and rapid shoot growth stages (ST2-ST4). Combined with transcriptome analysis, we found that DMR-related genes enriched in the auxin and jasmonic acid (JA) signal transduction, and other pathways closely related to plant growth. Intriguingly, CHH methylation was not involved in the rapid shoot growth, but strongly associated with shoot developmental time by gradually accumulating in transposable elements (TEs) regions. Overall, our results reveal the importance of DNA methylation in regulating the bamboo rapid shoot growth and suggest a role of DNA methylation associated with development time or age in woody bamboos.