Phosphate Starvation Triggers Transcriptional Changes in the Biosynthesis and Signaling Pathways of Phytohormones in Marchantia polymorpha

Abstract

Plant hormones are master regulators of developmental and genetic mechanisms to deal with diverse environmental cues. Upon phosphate (Pi) limitation, vascular plants modify phytohormone metabolism to coordinate diverse mechanisms to overcome such stress. However, the transcriptional program underlying the hormonal signaling in response to Pi scarcity in early branches of land plant phylogeny remains unclear. Therefore, we explored the transcriptional dynamics of key genes involved in auxin, cytokinin, ethylene, jasmonate, gibberellin, and abscisic acid metabolism in the early divergent land plant Marchantia polymorpha upon Pi starvation. Our RNAseq approach revealed major changes in genes associated with auxin and ethylene biosynthesis. Genes involved in cytokinin synthesis are repressed. Interestingly, genes involved in auxin and ethylene signaling, such as MpARF1 and MpARF2, are upregulated. In contrast, MpARRb is down-regulated. Moreover, genes involved in the synthesis of jasmonates were highly upregulated, but those related to signaling did not change in expression. Our data suggest that auxin and ethylene act as positive regulators of rhizoid development under Pi-limited conditions, whereas cytokinin may act as a negative regulator. The transcriptional behavior of some hormone-related genes in Marchantia is similar to those described in controlling root hair development in arabidopsis, maize, and rice, upon Pi scarcity.