Nostoc talks back: Temporal patterns of differential gene expression during establishment of the Anthoceros-Nostoc symbiosis

Abstract

Endosymbiotic association between hornworts and dinitrogen-fixing cyanobacteria form when the plant is limited for combined nitrogen (N). We generated RNA-Seq data to examine the temporal gene expression patterns during culture of N-starved Anthoceros punctatus in the absence and presence of the symbiotically competent cyanobacterium Nostoc punctiforme. Symbiotic nitrogenase activity commenced within 5 days of coculture reaching a maximal by 14 days. In symbiont-free gametophytes, chlorophyll content, chlorophyll fluorescence characteristics and transcription of genes encoding light harvesting and reaction center proteins, as well as the small subunit of ribulose-bisphosphate-carboxylase/oxygenase, were downregulated. The downregulation was complemented in a temporal pattern corresponding to the N. punctiforme provision of N2-derived ammonium. The impairment and complementation of photosynthesis was the most distinctive response of A. punctatus to N-starvation. Increases in transcription of ammonium and nitrate transporters and their N. punctiforme-dependent complementation was also observed. The temporal patterns of differential gene expression indicated N. punctiforme transmits signals to A. punctatus both prior to, and after its provision of fixed N. This is the only known temporal transcriptomic study during establishment of a symbiotic nitrogen-fixing association in this monophyletic evolutionary lineage of land plants.HighlightsTemporal RNA-Seq analysis revealed how symbiotic cyanobacteria impact plant partners’ global gene expression and elucidated the nature of bidirectional communications between the partners

Evolutionary genomic insights into cyanobacterial symbioses in plants

“…and an additional Azolla species. Additional transcriptomes for A. filiculoides, two other Azolla species, Azolla pinnata and Azolla caroliniana, and the hornwort A. punctatus exist (Brouwer et al, 2017;Chatterjee et al, 2021;de Vries et al, 2016;Li et al, 2020;Qi et al, 2018).…”

An optimised transformation protocol forAnthoceros agrestisand three more hornwort species

“…We successfully developed a modification of the Frangedakis et al 2021 protocol, that allowed us to obtain up to 55 stable independent transformant lines from 200 mg of tissue for the A. agrestis Bonn isolate and 103 stable transformant lines from 200 mg of tissue for the Oxford isolate We then tested whether the optimised transformation method is applicable to three other hornwort species: Anthoceros punctatus, Leiosporoceros dussii, and Phaeoceros carolinianus. A. punctatus has long been used as the study system for hornwort associations with cyanobacteria ( Nostoc punctiforme ) (Chatterjee et al 2022). Leiosporoceros dussii is the sister taxon to all hornworts (Duff et al 2007).…”

“…We then tested whether the optimised transformation method is applicable to three other hornwort species: Anthoceros punctatus, Leiosporoceros dussii, and Phaeoceros carolinianus. A. punctatus has long been used as the study system for hornwort associations with cyanobacteria (Nostoc punctiforme) (Chatterjee et al 2022). Leiosporoceros dussii is the sister taxon to all hornworts (Duff et al 2007).…”