Auxin minimum triggers developmental switch in the Arabidopsis root ($)

The root apex is an excellent tissue in which to study the mechanisms that control cell division and differentiation, as the cells produced by the root apical meristem form files of increasing age as they are moved away from the tip. In Arabidopsis, many mutant and reporter lines have contributed to a model in which the interplay between the hormones auxin and cytokinin (CK) control cell fate. Di Mambro and De Ruvo et al. explore this interaction further, using molecular genetic and computational modeling approaches. They uncover new roles for cytokinin in the control of the auxin minimum; in addition to CK’s control of the expression of the PIN auxin transporters, it also induces expression of enzymes that induce auxin conjugation and inactivation. They authors also show that the position of the auxin minimum determines the position of the transition zone between dividing and expanding cells and thus root meristem size. Proc. Natl. Acad. Sci. USA 10.1073/pnas.1705833114