Cytokinin functions as an asymmetric and anti-gravitropic signal in lateral roots (Nature Comms)

Lateral roots help plants to explore the soil and environmental conditions. Waidmann et al. took advantage of natural variants to understand lateral growth angle by analyzing gravitropic set point angle (GSA). Using Col-0 as a reference, lines that over- or under-respond (steeper or shallower root angle) were identified. From their genome-wide association study, the authors identified a SNP (T → G) that affects root angle in the CYTOKININ OXIDASE 2 (CKX2) gene; CKXs are cytokinin degrading enzymes. This SNP causes a change from isoleucine (I) to methionine (M) at the first amino acid in the mature enzyme, just after the position where the signal peptide is cleaved off. The CKX2^M version has reduced secretion signaling peptide cleavage and less transport to the apoplast. Consistently, CKX2^I but not CKX2^M can complement a ckx2-1 loss-of-function mutant. Additionally, the authors demonstrated that asymmetric cytokinin signaling plays a crucial role as an anti-gravitropic regulator in LRs. (Summary by Arif Asraf). Nature Comms. 10.1038/s41467-019-11483-4