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ARF3 and Cytokinin Regulate Floral Meristem Determinacy
Unlike shoot apical meristem (SAM) that produces the entire above-ground structures of a plant in an indeterminate manner, the floral meristem (FM) produces a defined number of floral organs then undergoes a programmed termination in process termed the FM determinacy. It is well known that the phytohormones cytokinin and auxin interact to conregulate many aspects of plant development, whether and how they interconnect in FM determinacy remain unclear.
With the goal of dissecting the role of cytokinin and auxin in FM determinacy, a research team led by LIU Xigang from the Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, found that AUXIN RESPONSE FACTOR3 (ARF3) can repress cytokinin biosynthesis and signaling to integrate the functions of AGAMOUS (AG) and auxin.
Following their previous report on the ARF3 function on the FM determinacy (Liu et al., 2014, The Plant Journal 80,629-641), they further found a de-repression of cytokinin activity in FM of arf3-29 and ag-10 arf3-29. Further analysis showed that ARF3 directly represses the expression of ISOPENTENYLTRANSFERASE (IPT) family genes and indirectly represses the LONELY GUY (LOG) family genes, both of which required by cytokinin biosynthesis. They also found ARF3 directly inhibits the expression of ARABIDOPSIS HISTIDINE KINASE4 (AHK4) that encodes a cytokinin receptor.
Furthermore, they found AG dynamically regulates the expression of ARF3. AG represses ARF3 transcription at stage 3-4 to maintenance FM activity through cell division, then promotes the expression of ARF3 at stage 5-6 for FM termination.
This work revealed a molecular link between AG and auxin/cytokinin and provides a novel knowledge to understand the mechanism of stem cell maintenance and termination in FM.
Related work has been published online in Plant Cell entitled “AUXIN RESPONSE FACTOR3 Regulates Floral Meristem Determinacy By Repressing Cytokinin Biosynthesis and Signaling”(DOI: )
A model of how ARF3 and cytokinin regulate FM determinacy (Image by IGDB)
LIU Xigang