SMXL7 As A Proteolytic Target Of Strigolactone Signalling Regulates Shoot Architecture In Arabidopsis

Shoot architecture broadly describes the arrangement of organs in the shoot system, including the number and size of lateral organs (leaves, flowers), the number of secondary shoot axes, and the spatial interconnections between them. Shoot system architectural characteristics strongly influence the productivity of many crop species, and have been selected for in both traditional and modern breeding schemes. Recently, SMXL6, SMXL7 and SMXL8, members of the small family of SMAX1-LIKE (SMXL) chaperonin-like proteins, have been identified as the proteolytic targets of strigolactone signalling. In this research, using Arabidopsis as model we saw rapid turnover of SMXL7 in root, stem, and leaves in response to rac-GR24. Furthermore, we demonstrated that SMXL7 localizes in the nucleus, and that this localization is necessary for both SMXL7 function and striglactone-mediated degradation. We provided more details of interactions of strigolactone signaling components in vivo. We assessed functionality of conserved domain in the SMXL7 protein through multiple genetic experiments, raising the possibility that there may be several distinct mechanisms at play downstream of SMXL7.1. Strigolactone triggers SMXL7 degradation across the plant body. We observed rapid turnover of SMXL7 in all cells of the Arabidopsis root meristem in 35S:SMXL7-YFP lines in response to GR24 treatment in a MAX2-and D14-dependent manner. We found that show that SL-triggered MAX2-dependent SMXL7 degradation is also detectable in the shoot in petioles and stems. We displayed that the SMXL6 and SMXL7 may form hetero-dimerization in nucleus, and their simultaneous degradation in response to treatment with rac-GR24. We demonstrated that the SMXL7 is predominantly expressed in vascular associated tissue and the transcriptional level of SMXL7 is not response to rac-GR24 treatment.2. Strigolactone signalling components function in nucleus.Here we show that SMXL7 functions in the nucleus, and is localized to discrete nuclear speckles. We identified a predicted nuclear localization signal (NLS) of SMXL7 by protein truncation assay. The deletion of NLS reduced the nuclear localization of SMXL7-YFP and had a little effect on rac-GR24 treatment without afunctionality. We demonstrated that strigolactone receptor DWARF 14 also functions primarily in the nucleus, where it can physically interact with both SMXL7 and the MAX2 protein in a strigolactone dependent manner.3. Functionality assay of conserved domains in the SMXL7 protein. We created multiple SMXL7 variants of the SMXL7 protein lacking or modifying defined protein motifs. We demonstrated that disruption of specific conserved domains in the SMXL7 protein affects its localization, strigolactone-induced degradation and activity. Using these protein variants we can dissect the role of SMXL7 in the control of shoot architecture.4. SMXL7 affectes Auxin transport. SMXL7 and PIN1 proteins can be found expressed in the same cells of the xylem parenchyma and vascular cambium. Both PIN1-GFP protein levels at the basal plasma membrane and auxin transport through stem are increased.5. Plant tissues in the shoot are broadly sensitive to SMXL7 activity. We displayed morphological phenotypic characterisation in relevant genetic background including number of shoot branching, plant height, branching angle, leaf morphology showing genotypes deficient in SMXL7 degradation show a clear dose-dependent in most tissues to increasing SMXL 7 copy number.6. The well-conserved EAR domain in SMXL7 is needed for some aspects of its function, but disposable for others. We find that different developmental processes show differential sensitivity to the loss of the EAR motif, suggesting SMXL7 may be a multi-functional protein, which regulates development through multiple downstream pathways.