Abstract
The plant hormone auxin regulates many aspects of plant growth and development. Recent progress has provided a scheme that F-box proteins, TIR1/AFBs, function as auxin receptors and degrade transcriptional repressors, AUX/IAAs, allowing ARFs to regulate transcription of auxin-responsive genes. However, auxin signaling in seed plants turned out to be highly complex, and their genetic redundancy prevents our understanding of the whole story. The liverwort, Marchantia polymorpha, belongs to a group of basal land plants and has a simple body plan and low genetic redundancy. We identified key genes for auxin-signaling in M. polymorpha, MpTIR1, MpIAA, MpARF1, and MpARF2, indicating the auxin-signaling machinery in M. polymorha is basically the same as in seed plants. Sequence comparison suggests a possibility that MpARF1 is regulated by miR167 as ARF6 and ARF8 in Arabidopsis. MpIAA has a glutamine-rich region in addition to the four functional domains conserved among AUX/IAAs. Expression of MpIAA that has a mutation in a putative degron reduced sensitivity to auxin. Using these plants with altered auxin-response, the effect of auxin on morphology of M. polymorpha is being investigated.
