New paper from the Schwechheimer and Hammes labs.
SHADE AVOIDANCE 4 is Required for Proper Auxin Distribution in the Hypocotyl.
Yanhua Ge, Fenglian Yan, Melina Zourelidou, Meiling Wang, Karin Ljung, Astrid Fastner, Ulrich Z. Hammes, Martin di Donato, Markus Geisler, Claus Schwechheimer and Yi Tao (2016)
The phytohormone auxin is involved in virtually every aspect of plant growth and development. Through polar auxin transport, auxin gradients can be established, which then direct plant differentiation and growth. Shade avoidance responses are well-known processes that require polar auxin transport. Here, we have identified a sav4 (shade avoidance 4) mutant that is defective in shade-induced hypocotyl elongation and basipetal auxin transport. SAV4 encodes an unknown protein with armadillo (ARM) repeat- and tetratricopeptide repeat (TPR)-like domains known to provide protein-protein interaction surfaces. C-terminally yellow fluorescent protein (YFP)-tagged SAV4 localizes to both the plasma membrane and the nucleus. Membrane-localized SAV4 displays a polar association with the shoot-ward plasma membrane domain in hypocotyl and root cells, which appears to be necessary for its function in hypocotyl elongation. Co-transfection of SAV4 and ABCB1 (ATP-binding cassette B 1) auxin transporter in tobacco revealed that SAV4 blocks ABCB1-mediated auxin efflux. We thus propose that polarly localized SAV4 acts to inhibit ABCB-mediated auxin efflux towards shoot and facilitates the establishment of proper auxin gradients.
