The SCAR/WAVE complex polarizes PAN receptors and promotes division asymmetry in maize

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Pre-mitotic establishment of polarity is a key event in the preparation of mother cells for asymmetric cell divisions that produce daughters of distinct fates, and ensures correct cellular patterning of tissues and eventual organ function. Previous work has shown that two receptor-like kinases, PANGLOSS2 (PAN2) and PAN1, and the small GTPase RHO GTPASE OF PLANTS (ROP) promote mother cell polarity and subsequent division asymmetry in developing maize stomata. PAN proteins become polarized prior to asymmetric cell division, however, the mechanism of this polarization is unknown. Here we show that the SCAR/WAVE regulatory complex, which activates the actin-nucleating ARP2/3 complex, is the first known marker of polarity in this asymmetric division model and is required for PAN polarization. These findings implicate actin, and specifically branched actin networks, in PAN polarization and asymmetric cell division.

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Figure 1: Synergistic relationship between brk and pan mutants.
Figure 2: BRK1–CFP localization and interaction with other SCAR complex members.
Figure 3: BRK1–CFP becomes polarized prior to PAN2–YFP and PAN1–YFP.
Figure 4: Brk1 and Brk3 are required for PAN polarization, but Pan1 and Pan2 are not required for BRK1 polarization.
Figure 5: SMC polarization timeline.
Figure 6: Model of SMC polarization.


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We thank Kaiyue Deng for collecting complementation data in Supplementary Fig. 2 and the BICD101 class of 2009 at UC San Diego for sequencing brk3 alleles. This work was supported by NSF grants IOS-1147265 to LGS, NSF-1027446 to AWS, and a New Scholar Award from the Ellison Medical Foundation to EJB.

Author information

M.R.F. and L.G.S. planned the experiments. M.R.F., Y.P., D.S., and H.N.C. performed the microscopy. M.R.F. performed the co-IP/western blots and M.R.F., B.Y., and E.J.B. performed the co-IP/MS. A.L. and A.W.S. made the –CFP and –YFP constructs and supplied transgenic plants. M.R.F., Y.P. and L.G.S. analysed the data. M.R.F. wrote the manuscript with input from other authors.

Correspondence to Michelle R. Facette or Laurie G. Smith.

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