The characterisation of SMG1 in the nonsense-mediated mRNA decay pathway of Physcomitrella patens

The regulation of gene expression is not simply confined to the activity of a promoter but can occur at many stages, including mRNA degradation.
Nonsense-mediated mRNA decay (NMD) is a eukaryotic mRNA decay pathway. It was first characterised as a pathway degrading transcripts with premature stop codons arising from mutations or alternative splicing. However,
NMD also directly targets many ‘non-aberrant’ transcripts and is important for normal growth and development. For example, NMD is needed for a normal response to pathogens in Arabidopsis thaliana and NMD is regulated during
mammalian brain development. In animals, it is well known that the kinase SMG1 activates the NMD pathway when a premature stop codon is recognised but no NMD-associated kinase has been characterised outside the animal
kingdom. Reported here is that SMG1, whilst missing from fungi and A. thaliana, is ubiquitous in the plant kingdom, functions in the NMD pathway of moss and is needed for normal moss development. An RNA-seq analysis of
transcripts regulated by SMG1 in moss revealed that NMD is important for regulating the unfolded protein response and is also involved in the DNA repair pathway. Taken together, SMG1 has been demonstrated to be an ancient kinase, which functions in the NMD pathway in moss. Furthermore, NMD is
important for normal moss development.