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Abstract The phytohormone cytokinin has diverse functions in plants, most of which have been primarily elucidated in the eudicotyledonous plant Arabidopsis (Arabidopsis thaliana). To further characterize the role of cytokinin in a monocot, we used CRISPR-Cas9 to generate rice (Oryza sativa) lines with frameshift alleles in genes encoding the 4 putative histidine kinase (HK) cytokinin receptors, resulting in all single and multiple mutant combinations. The hk3,4,5,6 quadruple mutant transcriptome was completely insensitive to cytokinin, suggesting that all transcription regulated through cytokinin signaling acts through these 4 HKs, despite the presence of a putative cytokinin-binding CHASE-containing Ser/Thr kinase in rice. Rice HKs functioned partially redundantly in diverse aspects of growth and development, with different HKs playing more prominent roles in various processes. This functional specialization was most striking in panicle architecture, where HK4 promoted fertility, HK3 and HK5 drove secondary branch formation, and HK6 drove primary branch formation. Furthermore, unlike Arabidopsis, cytokinin signaling was essential for shoot formation in rice, as the hk3,4,5,6 quadruple mutant was shootless, likely due to a failure to develop a shoot apical meristem. The necessity for shoot formation is consistent with one of the first roles of cytokinin uncovered by Skoog and Miller in the 1950s. Overall, this work elucidates the many roles of cytokinin perception throughout the lifespan of rice, some of which diverge from those known in Arabidopsis, highlighting the need to study alternative model systems.
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Cytokinin: From autoclaved DNA to two-component signaling
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.
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- PAR ID:
- 10541038
- Publisher / Repository:
- Oxford University
- Date Published:
- Journal Name:
- The Plant Cell
- Volume:
- 36
- Issue:
- 5
- ISSN:
- 1040-4651
- Page Range / eLocation ID:
- 1429 to 1450
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Plants constantly integrate environmental stimuli with developmental programs to optimize their growth and fitness. Excessive activation of the plant immune system often leads to decreased plant growth, a process known as the growth-defense tradeoff. Cytokinins are phytohormones that regulate cell division and plant yield, with important additional roles in nitrogen signaling, abiotic and biotic stress tolerance. Here, we show that constitutive activation of immunity suppresses cytokinin signaling and that complementation of the levels of cytokinin in Arabidopsis autoimmunity mutants reduces the growth tradeoff due to defense activation by changes in meristematic activity, resulting in increased yield and resistance to pathogens of both biotrophic and necrotrophic lifestyles. Thus, complementation of cytokinin suppression in the context of activated immunity may be targeted for increased crop productivity and resistance through genetic and chemical means. Our approach demonstrates targeting of phytohormone crosstalk for alleviating the growth-defense tradeoff, bypassing laborious and time-consuming identification and manipulation of causal genes, and indicate that similar approaches may be used for optimization of other traits in plants.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1093/plcell/koad327
