Control of Root Cap Formation by MicroRNA-Targeted Auxin Response Factors in Arabidopsis

TLDR

The plant root cap directs root tip growth, protects internal cells, and its cells are continuously produced from distal stem cells with auxin providing positional information for root distal organization. The study identifies ARF10 and ARF16, targeted by miR160, as controllers of root cap cell formation in Arabidopsis thaliana. Auxin and miR160 independently regulate ARF10 and ARF16 expression, producing a pattern that aligns with root cap development. Repression of ARF10/ARF16 by miR160 overexpression or arf10‑2 arf16‑2 mutants leads to uncontrolled cell division, blocked differentiation, a tumor‑like root apex, and loss of gravity sensing, demonstrating that ARF10 and ARF16 are indispensable for restricting the stem cell niche and promoting columella differentiation, while miR160‑uncoupled ARF16 production causes pleiotropic developmental effects.

Abstract

Abstract The plant root cap mediates the direction of root tip growth and protects internal cells. Root cap cells are continuously produced from distal stem cells, and the phytohormone auxin provides position information for root distal organization. Here, we identify the Arabidopsis thaliana auxin response factors ARF10 and ARF16, targeted by microRNA160 (miR160), as the controller of root cap cell formation. The Pro35S:MIR160 plants, in which the expression of ARF10 and ARF16 is repressed, and the arf10-2 arf16-2 double mutants display the same root tip defect, with uncontrolled cell division and blocked cell differentiation in the root distal region and show a tumor-like root apex and loss of gravity-sensing. ARF10 and ARF16 play a role in restricting stem cell niche and promoting columella cell differentiation; although functionally redundant, the two ARFs are indispensable for root cap development, and the auxin signal cannot bypass them to initiate columella cell production. In root, auxin and miR160 regulate the expression of ARF10 and ARF16 genes independently, generating a pattern consistent with root cap development. We further demonstrate that miR160-uncoupled production of ARF16 exerts pleiotropic effects on plant phenotypes, and miR160 plays an essential role in regulating Arabidopsis development and growth.