A division in PIN-mediated auxin patterning during organ initiation in grasses.
The hormone auxin plays a crucial role in plant morphogenesis. In the shoot apical meristem, the PIN-FORMED1 (PIN1) efflux carrier concentrates auxin into local maxima in the epidermis, which position incipient leaf or floral primordia. From these maxima, PIN1 transports auxin into internal tissues along emergent paths that pattern leaf and stem vasculature. In Arabidopsis thaliana, these functions are attributed to a single PIN1 protein. Using phylogenetic 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, including Arabidopsis. Additionally, we identified a conserved duplication of PIN1 in the grasses: PIN1a and PIN1b. In Brachypodium distachyon, SoPIN1 is highly expressed in the epidermis and is consistently polarized toward regions of high expression of the DR5 auxin-signaling reporter, which suggests 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 connecting new organs to auxin sinks in the older tissues. 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. Our results suggest that examination and modeling of PIN dynamics in plants outside of Brassicaceae will offer insights into auxin-driven patterning obscured by the loss of the SoPIN1 clade in Brassicaceae.
Plant and Microbial Biology Department, University of California at Berkeley, Berkeley, California, United States of America ; Plant Gene Expression Center, United States Department of Agriculture - Agricultural Research Service (USDA-ARS), Albany, California, United States of America.
Devin L
DL
O'Connor
Department of Computer Science, University of Calgary, Calgary, Alberta, Canada.
Adam
A
Runions
Plant and Microbial Biology Department, University of California at Berkeley, Berkeley, California, United States of America ; Plant Gene Expression Center, United States Department of Agriculture - Agricultural Research Service (USDA-ARS), Albany, California, United States of America.
Aaron
A
Sluis
Western Regional Research Center, United States Department of Agriculture - Agriculture Research Service (USDA-ARS), Albany, California, United States of America.
Jennifer
J
Bragg
Western Regional Research Center, United States Department of Agriculture - Agriculture Research Service (USDA-ARS), Albany, California, United States of America.
John P
JP
Vogel
Department of Computer Science, University of Calgary, Calgary, Alberta, Canada.
Przemyslaw
P
Prusinkiewicz
Plant and Microbial Biology Department, University of California at Berkeley, Berkeley, California, United States of America ; Plant Gene Expression Center, United States Department of Agriculture - Agricultural Research Service (USDA-ARS), Albany, California, United States of America.
Sarah
S
Hake
D000465:Algorithms; D017360:Arabidopsis / Q000235:genetics* / Q000502:physiology*; D058431:Brachypodium / Q000235:genetics / Q000502:physiology; D019295:Computational Biology; D003198:Computer Simulation; D035264:Flowers; D018506:Gene Expression Regulation, Plant; D017930:Genes, Reporter; D007091:Image Processing, Computer-Assisted; D007210:Indoleacetic Acids / Q000737:chemistry*; D018519:Meristem; D010802:Phylogeny; D018515:Plant Leaves / Q000378:metabolism; D006109:Poaceae / Q000235:genetics / Q000502:physiology*; D012984:Software; D003313:Zea mays / Q000235:genetics / Q000502:physiology
D007210:Indoleacetic Acids