A division in PIN-medicated patterning during lateral organ initiation in grasses

Authors: O'CONNOR, DEVON - University Of California; RUNIONS, ADAM - University Of Calgary; SLUIS, AARON - University Of California; Bragg, Jennifer; Vogel, John; PRUSINKIEWICZ, PRZEMYSLAW - University Of Calgary; Hake, Sarah

Submitted to: PLoS Computational Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2013
Publication Date: 1/30/2014
Citation: O'Connor, D.L., Runions, A., Sluis, A., Bragg, J.N., Vogel, J.P., Prusinkiewicz, P., Hake, S.C. 2014. A division in PIN-medicated patterning during lateral organ initiation in grasses. PLoS Computational Biology. 10(1):e1003447.

Interpretive Summary: The hormone auxin palys a crucial role in the morphogenesis of plants. In the shoot apical meristem, the PINFORED (PIN1) efflux carrier concentrates auxin into local maxima in the epidermis which localize incipient leaf or floral primordia. From theses maxima, PIN1 transports auxin into internal tissues along emergent paths that pattern stem vasculature. In Arabidopsis, these functions are attributtted to a single PIN1 related variants with distinct spatio-temporal distributions and polarization patterns during leaf initiation and vein patterning. By dividing the function between different PIN proteins, plants outside of Brassicaceae offer insights into auxin-driven patterning obscured by the fusion different functions in a single PIN1 protein in Brassicaceae including Arabidopsis.

Technical Abstract: Using phlyogenic and gene synteny analysis we identified an angiosperm PIN clade sister to PIN1, here termed SISter-of-PIN1 (soPIN1), which is present in all sampled angiosperms except for Brassicaceae. Additionally, we identified a conserved duplication of PIN1 in the grasses: PIN1a and PIN1b. In Brachypodium and maize, SoPIN1 is highly expressed in the epidermis and is consistently polarized toward regions of high expression of the DR5 auxin-signaling reporter, which suggets that SoPIN1 functions in the localization of new primordia. In contrast, PIN1a and PIN1b are highly expressed in internal tissues, suggesting a role in vascular patterning. PIN1b is expressed in broad regions spanning the space between new primordia and previously formed vasculature, suggesting a role in conecting new organs to auxin sinks in the older parts of the plant. Within these regions, PIN1a forms narrow canals that likely pattern future veins. Using a computer model, we reproduced the observed spatio-temporal expression and localization patterns of these proteins by assuming that SoPIN1 is polarized up the auxin gradient, and PIN1a and PIN1b are polarized to different degrees with the auxin flux. These results support the dual polarization model, previously formulated to explain the formation of convergence paoints and vein patterning, which assumes context-dependent polarization of a single type of PIN1.