Crossing paths: Investigating the role of auxin and cytokinin in 3D growth specification

One of the most important events in history was the colonization of land by plants approximately 470 million years ago. This transition coincided with, and was likely facilitated by, the evolution of 3-dimensional (3D) growth. 3D growth is an invariable and pivotal feature of all land plants, and the diverse morphologies exhibited across the globe are a result of the differential regulation of 3D growth processes. Yet, we know very little about how 3D growth is regulated at the genetic level.
Studies of 3D growth are difficult using flowering plants as 3D growth begins within the first few divisions of the zygote. Disrupting 3D growth in these plants would therefore cause embryo lethality and provide a narrow timeframe for experimental investigation. Conversely, in the moss Physcomitrium patens, 3D growth (gametophore development) is preceded by a protracted 2-dimensional (2D) filamentous phase that can be cultured indefinitely. P. patens does not need to initiate 3D growth to survive, and thus is an ideal model system to genetically dissect 3D growth. The 2D to 3D growth transition in P. patens is dependent on auxin and cytokinin signaling, is accompanied by highly coordinated changes in cell division plane orientation and culminates in the formation of gametophores with radially organised leaf-like phyllids. Auxin has been consistently implicated in cell division plane orientation within a broad range of developmental contexts and has been implicated as the 'instructive signal' for division plane orientation in developing gametophores.
We have isolated a number of 'no gametophores' (nog) mutants that fail to specify 3D growth because they exhibit defects in cell division orientation. This proposal will exploit these 'nog' mutants to unravel the complex auxin-cytokinin crosstalk underpinning the 2D to 3D growth transition in P. patens and will provide unprecedented insight into the regulation of 3D growth in plants.
Project Objectives:
-Identify the mutations in no gametophore' (nog) mutants that fail to specify 3D growth
- Characterize the auxin and cytokinin responses in nog mutants and obtain transcriptomes
-Recapitulate 3D growth defects through cell-specific disruption of auxin/cytokinin signaling