Journal
DEVELOPMENT
Volume 138, Issue 5, Pages 839-848Publisher
COMPANY BIOLOGISTS LTD
DOI: 10.1242/dev.061804
Keywords
Arabidopsis; Brassinosteroids; Growth; Cell proliferation; Cell-cell communication
Categories
Funding
- Fine Fellowship
- NSF [IOS-06-49389]
- Howard Hughes Medical Institute
- Israel Science Foundation [1498/09, 1603/09]
- [FP7-PEOPLE-IRG-2008]
- Biotechnology and Biological Sciences Research Council [BB/G023972/1, BB/D522603/1, BB/D019613/1] Funding Source: researchfish
- BBSRC [BB/D019613/1, BB/G023972/1] Funding Source: UKRI
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Multiple small molecule hormones contribute to growth promotion or restriction in plants. Brassinosteroids (BRs), acting specifically in the epidermis, can both drive and restrict shoot growth. However, our knowledge of how BRs affect meristem size is scant. Here, we study the root meristem and show that BRs are required to maintain normal cell cycle activity and cell expansion. These two processes ensure the coherent gradient of cell progression, from the apical to the basal meristem. In addition, BR activity in the meristem is not accompanied by changes in the expression level of the auxin efflux carriers PIN1, PIN3 and PIN7, which are known to control the extent of mitotic activity and differentiation. We further demonstrate that BR signaling in the root epidermis and not in the inner endodermis, quiescent center (QC) cells or stele cell files is sufficient to control root meristem size. Interestingly, expression of the QC and the stele-enriched MADS-BOX gene AGL42 can be modulated by BRI1 activity solely in the epidermis. The signal from the epidermis is probably transmitted by a different component than BES1 and BZR1 transcription factors, as their direct targets, such as DWF4 and BRox2, are regulated in the same cells that express BRI1. Taken together, our study provides novel insights into the role of BRs in controlling meristem size.
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