With approximately 22,000 species, bryophytes (hornworts, liverworts, and mosses) represent a major and diverse lineage of land plants. As 'pioneer plants', bryophytes can thrive in many extreme environments as they can endure the stresses of extreme temperatures, drought, low light and low nutrition. The moss Niphotrichum japonicum (Grimmiaceae, Grimmiales), is widely used for urban roof and wall greening because of its excellent environmental tolerance (high temperature, drought, strong light and nutrient limitation), providing a good candidate for studying the genetic basis underlying such high resilience.To investigate the genetic mechanisms of N. japonicum in response to heat stress, the research team from Shenzhen Fairy Lake Botanical Garden and collaborators assembled the chromosome-level genome of N. japonicum and revealed the response mechanism of mosses to heat stress using comparative transcriptomic.
Niphotrichum japonicum (photographed by Li Zhang)
The results show that N. japonicum had the smallest moss genome known to date, with a total length of 191.61 Mb, 14 pseudochromosomes, and a compact genome encoding 26,898 protein-coding genes, of which 10,019 are unique genes that may be associated with species-specific resistance. N. japonicum shared only one whole-genome duplication (WGD) event in its evolutionary history with Physcomitrium patens, whose autosomal structure was highly conserved, while the sex chromosomes were highly disordered and lacked synteny.
WGD of N. japonicum and inter-genomic synteny of mosses
Through comparative transcriptome analysis, the researchers elucidated the conservatism of heat-stress response mechanisms in N. japonicum, such as the up-regulation of HSPs, LEAs and reactive oxygen species (ROS) scavenging genes, and the down-regulation of PPR genes. The unique heat stress response mechanisms of N. japonicum were also revealed, including the genome-specific expansion of the plant self-incompatibility protein S1 (Self-incomp_S1) gene family and its up-regulation under heat stress, the functional divergence of duplicated genes, structural clusters of up-regulated genes, and co-expression of hub genes.
Weighted Gene Co-expression Network Analysis (WGCNA) and physical clusters of key regulatory genes on chromosomes
The results were published online on 18 October 2023 in the international journal Frontiers in Plant Science with the title "Chromosome-level genome assembly of Niphotrichum japonicump provides new insights into heat stress responses in mosses". This study is supported by the Scientific Foundation of the Urban Management Bureau of Shenzhen (Nos. 202005, 202203, 202106, 202302) and the Fairy Lake Botanical Garden (FLSF-2021-02). This paper is available at https://www.frontiersin.org/articles/10.3389/fpls.2023.1271357/full.
