The Microspherule protein 1 (MCRS1) homolog interacts with the Myb-like transcription factor DRMY1 and is essential for embryogenesis in Arabidopsis thaliana

The evolutionarily conserved Microspherule protein 1 (MCRS1) has diverse functions from transcriptional regulation to stabilization of microtubule minus ends in acentrosomal spindles in mammals. A previous study suggested that in the model plant Arabidopsis thaliana, inactivation of an MCRS1 homolog gene led to aborted embryogenesis. To test whether this lethality was caused by defects associated with transcription or mitosis, we used the heterozygous mcrs1 mutant to examine whether the gene was required for mitosis during gametogenesis. Results of reciprocal crosses between the mcrs1 mutant and the wild-type plant showed that the MCRS1 gene was dispensable for mitotic cell divisions associated with the development of both male and female gametophytes. An MCRS1-GFP fusion protein was expressed in the mcrs1 mutant and suppressed the mutation as reported by restored growth. This functional fusion protein exclusively localized to interphase nuclei and became undetectable during mitosis before returning to the reforming daughter nuclei. Affinity purification of the MCRS1-GFP protein resulted in consistent recovery of the Myb-like transcription factor DRMY1 (Developmentally Regulated Myb-like1) but not microtubule-associated factors. The association was further supported by the evidence of a direct interaction in living cells. Hence, the plant MCRS1 was concluded to play a role in the gene transcription in sporophyte development.