Abstract
In eukaryotes, protein kinases catalyze the transfer of a gamma-phosphate from ATP (or GTP) to specific amino acids in protein targets. In plants, protein kinases have been shown to participate in signaling cascades driving responses to environmental stimuli and developmental processes. Plant meristems are undifferentiated tissues that provide the major source of cells that will form organs throughout development. However, non-dividing specialized cells can also dedifferentiate and re-initiate cell division if exposed to appropriate conditions. Mps1 (Monopolar spindle) is a dual-specificity protein kinase that plays a critical role in monitoring the accuracy of chromosome segregation in the mitotic checkpoint mechanism. Although Mps1 functions have been clearly demonstrated in animals and fungi, its role in plants is so far unclear. Here, using structural and biochemical analyses here we show that Mps1 has highly similar homologs in many plant genomes across distinct lineages (e.g. AtMps1 in Arabidopsis thaliana). Several structural features (i.e. catalytic site, DFG motif and threonine triad) are clearly conserved in plant Mps1 kinases. Structural and sequence analysis also suggest that AtMps1 interact with other cell cycle proteins, such as Mad2 and MAPK1. By using a very specific Mps1 inhibitor (SP600125) we show that compromised AtMps1 activity hampers the development of A. thaliana seedlings in a dose-dependent manner, especially in secondary roots. Moreover, concomitant administration of the auxin IAA neutralizes the AtMps1 inhibition phenotype, allowing secondary root development. These observations let us to hypothesize that AtMps1 might be a downstream regulator of IAA signaling in the formation of secondary roots. Our results indicate that Mps1 might be a universal component of the Spindle Assembly Checkpoint machinery across very distant lineages of eukaryotes.
Highlights
Protein phosphorylation and dephosphorylation are among the most prominent and widespread post-translational modifications, being an essential part of most regulatory signaling cascades in eukaryotes and prokaryotes [1]
We found 156 plant Mps1 homologs that, along with the human Mps1 (hMps1), were submitted to multiple sequence alignment and the conserved region used for phylogenetic reconstructions
The clade containing hMps1 has only one A. thaliana gene product, AT1G77720, supporting the result obtained from pairwise comparisons (i.e. BLAST), which showed this gene as the A. thaliana best blast hit of hMps1
Summary
Protein phosphorylation and dephosphorylation are among the most prominent and widespread post-translational modifications, being an essential part of most regulatory signaling cascades in eukaryotes and prokaryotes [1]. EPKs have been implicated in signaling cascades that mediate responses to environmental stimuli and developmental processes [7,8,9,10]. Many of these signaling pathways can directly affect cell cycle regulation [11,12,13], such as the MAPK pathway – a major regulator of development, immunity and stress responses in plants [14]. Several retinoblastoma-related proteins are phosphorylated by cyclin-CDK complexes during specific cell cycle stages [22]. To the many similarities discussed above, there are remarkable differences between the animal and plant cell cycle, especially with regard to the metaphase plate formation and microtubule arrangement during cytokinesis [25]
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