SLOMO controls AUX1-mediated gravitropism through a non-proteolytic role for AUX1 ubiquitination

Abstract

Gravity-directed growth ensures that shoots and roots grow upwards and downwards, respectively. To achieve this, the organ’s angle with respect to gravity drives the asymmetric redistribution of the plant hormone auxin and consequently differential elongation creating a curvature of the organ. In addition to efflux transporters, the auxin influx transporter AUXIN RESISTANT 1 (AUX1) is essential for auxin redistribution during root gravitropism. Our results provide a biochemical framework that includes the F-box protein SLOMO affecting, possibly indirectly, AUX1 levels, and SLOMO controlling the ubiquitination of K261, K264, and K266, which affects AUX1 auxin transport properties. This reveals a novel, non-proteolytic role for SLOMO-mediated ubiquitination of AUX1.