BACKGROUND: Haspin kinases are mitotic kinases that are well-conserved from 
yeast to human. Human Haspin is a histone H3 Thr3 kinase that has important 
roles in chromosome cohesion during mitosis. Moreover, phosphorylation of 
histone H3 at Thr3 by Haspin in fission yeast, Xenopus, and human is required 
for accumulation of Aurora B on the centromere, and the subsequent activation of 
Aurora B kinase activity for accurate chromosome alignment and segregation. 
Although extensive analyses of Haspin have been carried out in yeast and 
animals, the function of Haspin in organogenesis remains unclear.
RESULTS: Here, we identified a Haspin kinase, designated AtHaspin, in 
Arabidopsis thaliana. The purified AtHaspin phosphorylated histone H3 at both 
Thr3 and Thr11 in vitro. Live imaging of AtHaspin-tdTomato and GFP-α-tubulin in 
BY-2 cells showed that AtHaspin-tdTomato localized on chromosomes during 
prometaphase and metaphase, and around the cell plate during cytokinesis. This 
localization of AtHaspin overlapped with that of phosphorylated Thr3 and Thr11 
of histone H3 in BY-2 cells. AtHaspin-GFP driven by the native promoter was 
expressed in root meristems, shoot meristems, floral meristems, and throughout 
the whole embryo at stages of high cell division. Overexpression of a kinase 
domain mutant of AtHaspin decreased the size of the root meristem, which delayed 
root growth.
CONCLUSIONS: Our results indicated that the Haspin kinase is a histone H3 
threonine kinase in A. thaliana. AtHaspin phosphorylated histone H3 at both Thr3 
and Thr11 in vitro. The expression and dominant-negative analysis showed that 
AtHaspin may have a role in mitotic cell division during plant growth. Further 
analysis of coordinated mechanisms involving Haspin and Aurora kinases will shed 
new light on the regulation of chromosome segregation in cell division during 
plant growth and development.