Understanding the Regulatory Network of Cytokinin Response Regulators in Adventitious Root development

Plants possess a remarkable regenerative capacity, which is extensively utilized in modern agriculture for the vegetative propagation of elite genotypes through stem cuttings. A crucial factor for successful propagation is the formation of adventitious roots (AR). Recent studies have identified three transcription factors from the ETHYLENE RESPONSE FACTOR (ERF) family, ERF113, ERF114, and ERF115, that act downstream of jasmonic acid (JA) and redundantly modulate cytokinin (CK) signaling to suppress AR initiation. However, the precise mechanism by which ERF115 regulates AR formation, whether through modulation of the CK biosynthesis pathway or CK-responsive genes, remains unclear. Although CK is known to inhibit AR formation, the underlying molecular mechanisms are still not fully understood. This study provides novel insights by demonstrating that ERF115 regulates the expression of CK-responsive genes, as evidenced by relative expression analysis in 35S:ERF115 and pERF115:ERF115: SRDX lines. Furthermore, this research explores the role of CK negative feedback regulators, Type-A ARRs, in AR initiation (ARI). Phenotypic analysis of single and double mutants revealed functional redundancy among Type-A ARRs, with arr5 arr6 double mutants exhibiting approximately a 50% reduction in AR numbers, suggesting that ARR5 and ARR6 play pivotal roles in AR development. Additionally, GUS reporter analysis indicated distinct spatio-temporal expression patterns of Type-A ARRs, with pARR5:GUS strongly localized in the hypocotyl during AR initiation. These findings suggest that Type-A and Type-B ARRs function within a coordinated regulatory network, integrating CK signaling to modulate AR development.