Aurora kinases in Arabidopsis and Physcomitrella

comparison WT vs aur double LR first divisionsPlant Aurora kinases are divided in two families, the Alpha and Beta type Auroras (Demidov et al., 2005). Whereas the Beta type Aurora of Arabidopsis localizes to centromeric regions, both Alpha type Auroras associate with the prophase spindle, kinetochore fibers during metaphase and anaphase and accumulate at the forming cell plate during cytokinesis, both in tobacco BY-2 cells as in Arabidopsis root cells.

 

Time lapse movie of an AURORA1-GFP expressing tobacco BY-2 cell going through mitosis. AURORA1 labels the prophase spindle, kinetochore spindle microtubules and the cell plate.

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A specific combination of two mutant alleles in Arabidopsis Aurora 1 and Aurora 2 yielded viable double mutant plants which are stunted and show division plane defects associated with formative divisions from embryogenesis onward with the most profound effects occurring during the first formative divisions leading to lateral root primordia development (Van Damme et al., 2011). How Alpha aurora kinases function in determining the orientation of the division plane in various formative divisions throughout plant development remains however completely unknown.

comparison WT vs aur double LR first divisions

Confocal sections of the first formative divisions during lateral root primordia development in Arabidopsis WT seedlings and the alpha aurora double mutant (aur1-2/aur2-2) expressing pPIN1::PIN1-GFP as membrane marker. While the first two formative divisions in WT are anticlinal (tangential to the growth axis), these divisions in the aurora double mutant are misoriented and periclinal (parallel to the growth axis).

 
 

Time lapse movie of initial lateral root primordium pericycle cell divisions in an Arabidopsis WT seedling and in the double mutant for aurora 1 and aurora 2 (aur1-2/aur2-2) expressing PIN1-GFP as a membrane marker and RFP-MBD to label the Mts. Whereas the initial divisions are anticlinal in a wild-type lateral root primordium and lead to the formation of two small adjacent cells, these divisions in the aurora double mutant are oblique and lead to an unstructured primordium lacking defined cell layers.

Like any kinase, Auroras function via the phosphorylation of their substrates. To investigate the causality of the aberrant division plane orientations, we are hunting for aurora kinase substrates. Preliminary evidence indicates that the animal aurora kinase phosphorylation motif is at least partially conserved in plant substrates of aurora kinases. We have identified the microtubule-bundling protein MAP65-1 as a substrate for alpha Aurora kinases (Boruc et al., 2017) and we are currently focusing on several family members of the TPX2-like protein family as well as other candidate substrate proteins, found using affinity purification followed by mass spectrometry analysis both in Arabidopsis and in the moss Physcomitrella patens. Moss has two aurora kinases and due to the availability of homologous recombination and the ease of imaging dividing protonemata cells, it provides an ideal model organism to study the role on Aurora in division plane determination.

References

  • Boruc J, Weimer AK, Stoppin-Mellet V, Mylle E, Kosetsu K, Cedeño C, Jaquinod M, Njo M, De Milde L, Tompa P, Gonzalez N, Inzé D, Beeckman T, Vantard M, Van Damme D. (2017). Phosphorylation of MAP65-1 by Arabidopsis Aurora Kinases Is Required for Efficient Cell Cycle Progression. Plant Physiol. 173, 582-599.
  • Demidov D., Van Damme D., Geelen D., Blattner F.R., Houben A. (2005). Identification and dynamics of two classes of aurora-like kinases in Arabidopsis and other plants. Plant Cell 17, 836-848.
  • Van Damme D., De Rybel B., Gudesblat G., Demidov D., Grunewald W., De Smet I., Houben A., Beeckman T. and Russinova E. (2011). Arabidopsis alpha Aurora kinases function in formative cell division plane orientation. Plant Cell 23, 4013-4024.