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Abstract The gaseous plant hormone ethylene is a key developmental and growth regulator, and a pivotal endogenous response signal to abiotic and biotic interactions, including stress. Much of what is known about ethylene biosynthesis, perception, and signaling comes from decades of research primarily in Arabidopsis thaliana and other eudicot model systems. In contrast, detailed knowledge on the ethylene pathway and response to the hormone is markedly limited in maize (Zea mays L.), a global cereal crop that is a major source of calories for humans and livestock, as well as a key industrial biofeedstock. Recent reports of forward screens and targeted reverse genetics have provided important insight into conserved and unique differences of the ethylene pathway and downstream responses. Natural and edited allelic variation in the promoter regions and coding sequences of ethylene biosynthesis and signaling genes alters maize shoot and root architectures, and plays a crucial role in biomass and grain yields. This review discusses recent advances in ethylene research in maize, with an emphasis on the role of ethylene in regulating growth and development of the shoot and root systems, and ultimately how this crucial hormone impacts plant architecture and grain yield. 

Abstract Since its first identification in the 1950s as a regulator of cell division, cytokinin has been linked to many physiological processes in plants, spanning growth and development and various responses to the environment. Studies from the last two and one-half decades have revealed the pathways underlying the biosynthesis and metabolism of cytokinin and have elucidated the mechanisms of its perception and signaling, which reflects an ancient signaling system evolved from two-component elements in bacteria. Mutants in the genes encoding elements involved in these processes have helped refine our understanding of cytokinin functions in plants. Further, recent advances have provided insight into the mechanisms of intracellular and long-distance cytokinin transport and the identification of several proteins that operate downstream of cytokinin signaling. Here, we review these processes through a historical lens, providing an overview of cytokinin metabolism, transport, signaling, and functions in higher plants.