SMAX1-LIKE7 Signals from the Nucleus to Regulate Shoot Development in Arabidopsis via Partially EAR Motif-Independent Mechanisms.
Strigolactones (SLs) are hormonal signals that regulate multiple aspects of shoot architecture, including shoot branching. Like many plant hormonal signaling systems, SLs act by promoting ubiquitination of target proteins and their subsequent proteasome-mediated degradation. Recently, SMXL6, SMXL7, and SMXL8, members of the SMAX1-LIKE (SMXL) family of chaperonin-like proteins, have been identified as proteolytic targets of SL signaling in Arabidopsis thaliana However, the mechanisms by which these proteins regulate downstream events remain largely unclear. Here, we show that SMXL7 functions in the nucleus, as does the SL receptor, DWARF14 (D14). We show that nucleus-localized D14 can physically interact with both SMXL7 and the MAX2 F-box protein in a SL-dependent manner and that disruption of specific conserved domains in SMXL7 affects its localization, SL-induced degradation, and activity. By expressing and overexpressing these SMXL7 protein variants, we show that shoot tissues are broadly sensitive to SMXL7 activity, but degradation normally buffers the effect of increasing SMXL7 expression. SMXL7 contains a well-conserved EAR (ETHYLENE-RESPONSE FACTOR Amphiphilic Repression) motif, which contributes to, but is not essential for, SMXL7 functionality. Intriguingly, different developmental processes show differential sensitivity to the loss of the EAR motif, raising the possibility that there may be several distinct mechanisms at play downstream of SMXL7.
Sainsbury Laboratory, University of Cambridge, Cambridge CB2 1LR, United Kingdom Rice Research Institute, Sichuan Agricultural University, Chengdu 611130, China.
Yueyang
0000-0002-7427-1028
Y
Liang
Sainsbury Laboratory, University of Cambridge, Cambridge CB2 1LR, United Kingdom.
Sally
0000-0002-5520-1331
S
Ward
Rice Research Institute, Sichuan Agricultural University, Chengdu 611130, China.
Ping
P
Li
Sainsbury Laboratory, University of Cambridge, Cambridge CB2 1LR, United Kingdom ol235@cam.ac.uk t.a.bennett@leeds.ac.uk.
Tom
0000-0003-1612-4019
T
Bennett
Sainsbury Laboratory, University of Cambridge, Cambridge CB2 1LR, United Kingdom ol235@cam.ac.uk t.a.bennett@leeds.ac.uk.
Ottoline
0000-0003-2161-3829
O
Leyser
D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000502:physiology; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D018520:Plant Shoots / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology
D029681:Arabidopsis Proteins; C000611064:DWARF14 protein, Arabidopsis; D047908:Intracellular Signaling Peptides and Proteins; D011956:Receptors, Cell Surface; C587487:SMAX1 protein, Arabidopsis