Abstract
The size of an organism is genetically determined, yet how a plant or animal achieves its final size is largely unknown. The shoot of higher plants has a simple conserved body plan based on three major tissue systems: the epidermal (L1), sub-epidermal (L2) and inner ground and vascular (L3) tissues. Which tissue system drives or restricts growth has been a subject of debate for over a century1,2,3,4. Here, we use dwarf, brassinosteroid biosynthesis and brassinosteroid response mutants in conjunction with tissue-specific expression of these components as tools to examine the role of the epidermis in shoot growth. We show that expression of the brassinosteroid receptor or a brassinosteroid biosynthetic enzyme in the epidermis, but not in the vasculature, of null mutants is sufficient to rescue their dwarf phenotypes. Brassinosteroid signalling from the epidermis is not sufficient to establish normal vascular organization. Moreover, shoot growth is restricted when brassinosteroids are depleted from the epidermis and brassinosteroids act locally within a leaf. We conclude that the epidermis both promotes and restricts shoot growth by providing a non-autonomous signal to the ground tissues.
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Acknowledgements
We thank Y. Belkhadir, M. Chen, N. Geldner and X. Wu for many thoughtful discussions and critical comments on the manuscript. We thank P. Sawchenko, LNSF, for access to microtomy, S. Mora-Garcia for help at the initial stage of the project and T. Gabi, S. Kim, E. Ballon-Landa, C. Butterfield and Z. Smith for technical assistance. This work was supported by grants from the National Science Foundation and the USDA to J.C. and by The Salk Institute and a Vaadia-BARD Postdoctoral Fellowship from BARD, The United States–Israel Binational Agricultural Research and Development Fund to S.S.-G. J.C. is an investigator of the Howard Hughes Medical Institute.
Author Contributions S.S.-G. and J.C. conceived and designed the experiments. S.S.-G. performed the experiments. C.P. performed plant anatomical sections. S.S.-G. and J.C. analysed the data and wrote the paper.
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Savaldi-Goldstein, S., Peto, C. & Chory, J. The epidermis both drives and restricts plant shoot growth. Nature 446, 199–202 (2007). https://doi.org/10.1038/nature05618
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DOI: https://doi.org/10.1038/nature05618