ARR2

ARR2, short for Arabidopsis Response Regulator 2, is a gene in the model plant Arabidopsis thaliana that encodes a transcription factor-like protein and is classified as a type-B Arabidopsis response regulator (ARR) within the plant cytokinin signaling pathway. Like other ARRs, ARR2 participates in transducing cytokinin signals to regulate gene expression.

Activation occurs when cytokinin signaling triggers phosphorylation by histidine phosphotransfer proteins, after which ARR2 localizes to the nucleus and modulates transcription of cytokinin-responsive genes. ARR2 commonly acts in partnership with other ARRs and signaling components to form regulation networks that modulate developmental processes.

ARR2 expression is induced by cytokinins and is observed in multiple tissues, including shoots and roots, with spatial-temporal patterns that reflect developmental stages and environmental conditions. Its activity contributes to control of organogenesis, such as leaf and shoot development, and root system architecture through interactions with other hormone pathways, notably auxin and light signaling.

Genetic studies show that loss- and gain-of-function mutations in ARR2 alter plant responses to cytokinin, affecting aspects of development and the sensitivity of tissues to cytokinin treatment. These phenotypes reinforce ARR2's role as a positive regulator in certain cytokinin responses within a broader regulatory network.

Because ARR2 is part of a conserved multi-component signaling module, it is widely cited in discussions of plant hormone signaling and hormone cross-talk, and remains a focus for understanding how cytokinins influence plant growth and adaptation.