PRJNA589193: The rice pseudo phosphotransfer proteins are negative regulators of endogenous cytokinin signaling and affect multiple aspects of growth and development.

Summary: The phytohormone cytokinin plays a significant role in nearly all aspects of plant growth and development. Cytokinin signaling has primarily been studied in the dicot model Arabidopsis, with relatively little work done in monocots, which include rice (Oryza sativa) and other cereals of agronomic importance. The cytokinin signaling pathway is a phosphorelay comprised of the histidine kinase receptors (HKs), the authentic histidine phosphotransfer proteins (AHPs), and the type-B Response Regulators (ARRs). Two negative regulators of cytokinin signaling have been identified: the type-A ARRs, which are cytokinin primary response genes, and the pseudo histidine phosphotransfer proteins (PHPs), which lack the His residue required for phosphorelay. Here, we describe the role of the PHP genes from rice. Phylogenic analysis indicates that the PHPs are generally first found in the genomes of gymnosperms and that they arose independently in monocots and dicots. Consistent with this, the three rice PHPs fail to complement an Arabidopsis php mutant (ahp6). Disruption of the three PHPs results in a molecular phenotype consistent with these elements acting as negative regulators of basal cytokinin signaling, including the constitutive up-regulation of a number of type-A RR and cytokinin oxidase genes. The triple php mutant affects multiple aspects of rice growth and development, including shoot morphology, panicle architecture and seed fill. However, in contrast to Arabidopsis, disruption of the rice PHPs does not affect root vascular patterning, suggesting that while many aspects of key signaling networks are conserved between monocots and dicots, the molecular components regulating some processes are distinct.

Overall Design: The phytohormone cytokinin plays a significant role in nearly all aspects of plant growth and development. Cytokinin signaling has primarily been studied in the dicot model Arabidopsis, with relatively little work done in monocots, which include rice (Oryza sativa) and other cereals of agronomic importance. The cytokinin signaling pathway is a phosphorelay comprised of the histidine kinase receptors (HKs), the authentic histidine phosphotransfer proteins (AHPs), and the type-B Response Regulators (ARRs). Two negative regulators of cytokinin signaling have been identified: the type-A ARRs, which are cytokinin primary response genes, and the pseudo histidine phosphotransfer proteins (PHPs), which lack the His residue required for phosphorelay. Here, we describe the role of the PHP genes from rice. Phylogenic analysis indicates that the PHPs are generally first found in the genomes of gymnosperms and that they arose independently in monocots and dicots. Consistent with this, the three rice PHPs fail to complement an Arabidopsis php mutant (ahp6). Disruption of the three PHPs results in a molecular phenotype consistent with these elements acting as negative regulators of basal cytokinin signaling, including the constitutive up-regulation of a number of type-A RR and cytokinin oxidase genes. The triple php mutant affects multiple aspects of rice growth and development, including shoot morphology, panicle architecture and seed fill. However, in contrast to Arabidopsis, disruption of the rice PHPs does not affect root vascular patterning, suggesting that while many aspects of key signaling networks are conserved between monocots and dicots, the molecular components regulating some processes are distinct.