ABCB21 regulates auxin levels in cotyledons, pericycle and leaves (Frontiers Plant Science)

Auxin activity is maintained through regulated biosynthesis, metabolism and transport. In this paper Jenness et al. characterized the physiological significance of a known IAA transporter, ABCB21 (ATP BINDING CASSETTE TRANSPORTER subfamily B member 21) in Arabidopsis. ABCB21 transports shoot derived auxin in the rootward direction, and a transcriptional fusion of ABCB21 regulatory elements fused to GUS showed expression in the root pericycle, cotyledons and tissue near veins of rosette leaves, as well as in response to wounding. The loss-of-function mutant, abcb21 has delayed lateral root emergence and reduced rootward IAA transport, and increased cotyledon size (potentially due to increased cell expansion). The triple mutant abcb1 abcb19 abcb21 (other known IAA transporters) has enhanced leaf defects. These results confirm a physiological role for ABCB21. (Summary for Suresh Damodaran) Front. Plant Sci. 10.3389/fpls.2019.00806