The Multi-omic Approaches Reveal The Molecular Mechanism Of The Antarctic Moss Pohlia Nutans In Response To Environmental Stresses

The Antarctic continent has the harsh natural environments and fragile ecosystems.Bryophytes are the most important vegetation on the Antarctic continent.In this study,using the Antarctic moss P.nutans as research subject,the main research findings are as followed:(1)The genome sequencing and adaptive evolution analysis of Antarctic moss.Bryophytes are the most important plant group in the Antarctic continent,but there are little knowledges on the genomic characteristics and adaptive evolutionary analysis of polar bryophytes.In this study,we used third-generation Pac Bio sequencing,second-generation Illumina sequencing,and high-throughput chromosome conformation capture(Hi-C)technology to assemble the genome of P.nutans.The genome size of P.nutans was 698.20 Mb.The genome had 22 chromosomes and encoded 40,905 genes.The main repeat sequences in the genome of P.nutans were transposable elements,accounting for 63.79% of the entire genome sequences;we predicted that the whole-genome duplications incidents occurred about5.85 million years ago in P.nutans.Through comparative genomic analysis among different species,we found that there were 7,807 and 635 gene families in the genome of P.nutans significantly expanded and contracted,respectively.The expanded gene family was mainly involved in metabolite synthesis and environmental adaptation.(2)Integrated transcriptomic and metabolomic analyses of the response to UV-B radiationAntarctic organisms are consistently suffering from multiple environmental pressures,especially the strong UV-B radiation caused by the loss of the ozone layer.The molecular mechanisms of Antarctic plants resisting UV-B radiation are largely unknown.In this study,the Illumina Hi Seq sequence platform was used to obtain the transcriptome of P.nutans under UVB radiation.A total of 19,045 differentially expressed genes and 1,459 differentially expressed lnc RNA were obtained.Through functional annotation,we found that differentially expressed genes and lnc RNAs were enriched in plant-pathogen interaction and flavonoid biosynthesis pathway significantly.Then,a total of 451 metabolites were detected using widely targeted metabolomics analysis.Based on comprehensive analyses of transcriptome and metabolomic data,we found that differentially expressed genes and metabolites related to flavonoids biosynthesis,as well as differentially expressed lnc RNA,had co-expression patterns.(3)Integrated transcriptomic and metabolomic analyses of the response to drought stressIn eastern Antarctica,summer temperatures are gradually decreasing,and the climates are also becoming dry.The molecular mechanism of adaptation of Antarctic plants to drought stress has rarely been reported.We found that drought stress made the gametophytes turn yellow and curled,and enhanced the contents of malondialdehyde and proline,and the activities of antioxidant enzymes.A total of 2,451 differentially expressed genes and 354 differentially expressed metabolites were detected through high-throughput sequencing technology and widely targeted metabolome.The representative DEGs were mainly involved in ROS-scavenging and detoxification,flavonoid metabolism pathway,plant hormone signaling pathway,lipids metabolism pathway,transcription factors and signal-related genes.Flavonoids and lipids were the most abundant metabolites and they accounted for 41.53% of the significantly changed metabolites.In addition,integrated transcriptome and metabolome analyses revealed co-expression patterns of flavonoid and long-chain fatty acid biosynthesis genes and their metabolites.Taken together,we firstly completed the genome sequencing of a polar bryophyte and successfully assembled a chromosome level and high-quality genome.Using transcriptome and metabolome analyses,we revealed the characteristics of gene transcription and metabolites changes and response networks of Antarctic moss under UV-B radiation and drought stress.Our studies uncovered the molecular mechanism of adaptation to Antarctic extreme environments in the basal land plants.This will expand our understanding of the evolution of early terrestrial plants and their adaptation to polar terrestrial environments,providing an important theoretical basis for evaluating the impact of coastal climate change on Antarctic terrestrial plants.