Plant J. Plants have the capacity of building several vitamin compounds that animals must uptake with their diet instead. Some of these pathways, such as the B1 pathway, are extremely complex and still not completely elucidated.
The At5g32470 gene was identified as a new thiamine monophosphate (TMP) phosphatase by Mimura et al, 2016. The analysis of a new mutant line named pale green 1 corroborated their findings. However, Hsieh et al now raise the hypothesis that this protein is located in the mitochondrion rather than in the cytosol as previously concluded. If these data are confirmed, this would imply a transport mechanism of TMP from the chloroplast where it is produced to the mitochondrion, as well as a passage of thiamine back to the cytosol for conversion to the active form thiamine triphosphate (TPP) by thiamine pyrophosphatases, which, to our knowledge, are located in the cytosol.
Interestingly, the pale green 1 line comes from a T-DNA insertion collection but the mutation in the At5g32470 is a collateral point mutation. (Summary by Elisa Dell’Aglio) Plant J. DOI: 10.1111/tpj.13552 (See also Mimura et al, Plant Cell 10.1105/tpc.16.00600)