| Abstract |
Root system architecture (RSA) influences the acquisition of heterogeneously dispersed soil nutrients. Cytokinin and C-TERMINALLY ENCODED PEPTIDE (CEP) hormones affect RSA, in part by controlling the angle of lateral root (LR) growth. Both hormone pathways converge on CEP DOWNSTREAM 1 (CEPD1) and CEPD2 to control primary root growth, however, a role for CEPDs in controlling the growth angle of LRs is unknown. Using phenotyping combined with genetic and grafting approaches, we showed that CEP hormone-mediated shallower LR growth required cytokinin synthesis and cytokinin perception in roots via ARABIDOPSIS HISTIDINE KINASE 2 (AHK2) and AHK3. Consistently, cytokinin synthesis and ahk2,3 mutants phenocopied the steeper-root phenotype of cep receptor 1 (cepr1) mutants on agar plates, and CEPR1 was required for trans-Zeatin (tZ)-type cytokinin-mediated shallower LR growth. In addition, cepd1,2 was less sensitive to CEP and tZ and showed basally steeper LRs on agar plates. Cytokinin and CEP pathway mutants were grown in rhizoboxes to define the role of these pathways in controlling RSA. Only cytokinin receptor mutants and cepd1,2 partially phenocopied the steeper-rooted phenotype of cepr1 mutants. These results show CEP and cytokinin signaling intersect to promote shallower LR growth, but additional components contribute to the cepr1 phenotype in soil.
|
