The cytokinin response factors modulate root and shoot growth and promote leaf senescence in Arabidopsis

Summary The cytokinin response factors ( CRF s) are a group of related AP 2/ ERF transcription factors that are transcriptionally induced by cytokinin. Here we explore the role of the CRF s in Arabidopsis thaliana growth and development by analyzing lines with decreased and increased CRF function. While single crf mutations have no appreciable phenotypes, disruption of multiple CRF s results in larger rosettes, delayed leaf senescence, a smaller root apical meristem (RAM), reduced primary and lateral root growth, and, in etiolated seedlings, shorter hypocotyls. In contrast, overexpression of CRF s generally results in the opposite phenotypes. The crf1 , 2 , 5 , 6 quadruple mutant is embryo lethal, indicating that CRF function is essential for embryo development. Disruption of the CRF s results in partially insensitivity to cytokinin in a root elongation assay and affects the basal expression of a significant number of cytokinin‐regulated genes, including the type‐A ARR s, although it does not impair the cytokinin induction of the type‐A ARR s. Genes encoding homeobox transcription factors are mis‐expressed in the crf1 , 3 , 5 , 6 mutant, including STIMPY / WOX 9 that is required for root and shoot apical meristem maintenance roots and which has previously been linked to cytokinin. These results indicate that the CRF transcription factors play important roles in multiple aspects of plant growth and development, in part through a complex interaction with cytokinin signaling.