Abstract
Organ size control is of particular importance for developmental biology and agriculture, but the mechanisms underlying organ size regulation remain elusive in plants. Meristemoids, which possess stem cell-like properties, have been recognized to play important roles in leaf growth. We have recently reported that the Arabidopsis F-box protein STERILE APETALA (SAP)/SUPPRESSOR OF DA1 (SOD3) promotes meristemoid proliferation and regulates organ size by influencing the stability of the transcriptional regulators PEAPODs (PPDs). Here we demonstrate that KIX8 and KIX9, which function as adaptors for the corepressor TOPLESS and PPD, are novel substrates of SAP. SAP interacts with KIX8/9 and modulates their protein stability. Further results show that SAP acts in a common pathway with KIX8/9 and PPD to control organ growth by regulating meristemoid cell proliferation. Thus, these findings reveal a molecular mechanism by which SAP targets the KIX-PPD repressor complex for degradation to regulate meristemoid cell proliferation and organ size.
Highlights
How plants control final organ size is an intriguing question in developmental biology
We have previously demonstrated that the Arabidopsis F-box protein STERILE APETALA (SAP)/SUPPRESSOR OF DA1 (SOD3) controls organ size by promoting meristemoid proliferation
We found that SAP interacts with KIX8/9 in vitro and in vivo, and modulates their protein stability
Summary
How plants control final organ size is an intriguing question in developmental biology. In the tip region of the leaf, cell division gradually ceases and cells begin to differentiate and expand. This cell differentiation domain spreads down, forming a cell-cycle arrest front that moves toward the leaf base[8, 9]. While most cells behind this cell-cycle arrest front exit cell division, the meristemoid cells that possess stem cell-like properties divide a few rounds and form stomata or epidermal pavement cells [10, 11]. This proliferation of meristemoid cells is specific for dicot plants [12]. In Arabidopsis, meristemoid cells generate about 48% of all pavement cells in leaves[13], indicating that the amplifying division of these meristemoid cells contributes significantly to leaf size
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