Abstract
Cell polarity is a fundamental feature underlying cell morphogenesis and organismal development. In the Arabidopsis stomatal lineage, the polarity protein BASL controls stomatal asymmetric cell division. However, the cellular machinery by which this intrinsic polarity site is established remains unknown. Here, we identify the PRAF/RLD proteins as BASL physical partners and mutating four PRAF members leads to defects in BASL polarization. Members of PRAF proteins are polarized in stomatal lineage cells in a BASL-dependent manner. Developmental defects of the praf mutants phenocopy those of the gnom mutants. GNOM is an activator of the conserved Arf GTPases and plays important roles in membrane trafficking. We further find PRAF physically interacts with GNOM in vitro and in vivo. Thus, we propose that the positive feedback of BASL and PRAF at the plasma membrane and the connected function of PRAF and GNOM in endosomal trafficking establish intrinsic cell polarity in the Arabidopsis stomatal lineage.
Highlights
Cell polarity is a fundamental feature underlying cell morphogenesis and organismal development
Members of the PRAF family in Arabidopsis were recently named as RCC1like domain (RLD) proteins that interact with the polarized LAZY1-like proteins and participate in the regulation of gravitropism signaling in root columella cells[29]
We identify members of the PRAF/RLD protein family as physical partners of the intrinsic polarity protein BASL in the stomatal lineage cells
Summary
Cell polarity is a fundamental feature underlying cell morphogenesis and organismal development. In the Arabidopsis stomatal lineage, the polarity protein BASL controls stomatal asymmetric cell division. Members of PRAF proteins are polarized in stomatal lineage cells in a BASL-dependent manner. We propose that the positive feedback of BASL and PRAF at the plasma membrane and the connected function of PRAF and GNOM in endosomal trafficking establish intrinsic cell polarity in the Arabidopsis stomatal lineage. During stomatal ACD, the plant-specific protein BASL defines an intrinsic polarity pole by asymmetrically distributing to the cell cortex[8] (Fig. 1a), where BASL assembles a polarity complex comprised of scaffold proteins (POLAR and BRX)[9,10] and signaling regulators (YODA kinase, BIN2 GSK3-like kinases, and BSL phosphatases)[11,12,13]. NYFP cYFP-PRAF4ΔBRX cYFP compromised stomatal division and abnormal patterning of epidermal cells in Arabidopsis[8] (Supplementary Fig. 1a)
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