Co-option of transcriptional hub expanded triangular functional interactions among nutrients during plant terrestrialzation
Plant nitrate, phosphate, and sucrose responses create a complex molecular network fine-tuned for growth and survival. This triangular interplay, crucial for the adaptability of terrestrial plants, allows the availability of one nutrient to influence plant responses to others. However, the origins and functional repurposing of this complex network for plant terrestrialization remain scarcely understood. By delving into the time-series transcriptome responses to nitrate, phosphate, and sucrose in the bryophyte Marchantia polymorpha and its streptophycean algal relatives Klebsormidium nitens, we observed convergent yet largely species-specific regulatory circuits in nutrient response. A key gene regulatory network (GRN) module centered on MpCSD, MpERF20, and MpHD9 was found to govern the hierarchical responses and crosstalk among the three nutrients in M. polymorpha. In K. nitens, these transcription factors were involved in nutrient responses but were co-opted during phytoterrestrialization to serve additional functions. Further network perturbation experiments validated the extensive evolution of transcriptional targets of these regulatory circuits, with cytokinin responsive genes being recruited exclusively into macronutritional GRNs in M. polymorpha thus optimizing nutrient response. Our findings illuminate the evolutionary strategies employed to redeploy the triad of nutrient interactions during the adaptation of ancestral green plants to terrestrial habitats. Overall design: To study the macronutritional GRN co-option during terrestrialization, parrallel transcriptome study was performed in K. nitens and M. polymorpha, in which five time points including cotrol, nitrate/phosphate/sucrose stravation for five days, and then nutrient resupply for 6h, 24h, and 72h. Three important transcription factors MpCSD, MpERF20, and MpHD9 were identified in this analysis. Furthermore, RNAseq experiments were performed in the three different knock-out mutants by exposure to nitrate/phosphate/sucrose stravation for 5 days.