The role of KANADI in regulating thallus and gametangiophore development in Marchantia.

Liam Briginshaw, Eduardo Flores-Sandoval, John P. Alvarez, John L. Bowman

The liverwort Marchantia possesses a single ortholog of the KANADI transcription factor family. KANADI transcription factors form a land plant-specific clade characterised by a GARP DNA-binding domain and two highly conserved repressor-like domains.. In Arabidopsis, the antagonistic activities of KANADI and Class III HD-Zip transcription factors are responsible for regulating adaxial-abaxial polarity in lateral organs, and there is some evidence to suggest that they may additionally regulate shade-induced growth. We investigated the role of MpKAN by generating loss- and gain-of-function alleles, to see whether KANADI transcription factors have conserved roles in regulating tissue polarity and/or FR-induced responses in the gametophyte stage of the life cycle, which would then have necessarily been co-opted during the evolution of sporophyte dominance in vascular plants.

When grown under white light, Mpkan null mutants have an increased rate of branching and fewer air pores and gemmae cups than in wild-type. DEX-inducible MpKAN-GR expression with the MpEF1 constitutive promoter causes repression of growth from the notch and the development of unusual filament-like outgrowths dorsally. Under far-red (FR)-enriched light conditions, loss-of-function mutants display delayed initiation of gametangiophores in both sexes, with gametangiophores ultimately exhibiting thallus-like characteristics. No obvious abnormalities in tissue polarity were observed in the gametophytes of loss-of-function mutants and gain-of-function transformants. We propose that MpKAN acts as part of the pathway regulating the transition from regular thallus development to sexual development under FR-enriched light conditions, suggesting that KANADI may have a conserved role in controlling FR-regulated growth responses in land plants.

Presenting Author:  Liam Briginshaw

Author Affiliation: School of Biological Sciences, Monash Uni, Melbourne VIC 3800