The Arabidopsis TUMOR PRONE5 (TUP5) gene encodes an acetylornithine
aminotransferase required for arginine biosynthesis and root meristem
maintenance in blue light.
Arginine is an essential amino acid necessary for protein synthesis and is
also a nitrogen storage compound. The genes encoding the enzymes of arginine
biosynthesis in plants are not well characterized and have mainly been
predicted from homologies to bacterial and fungal genes. We report the cloning
and characterization of the TUMOR PRONE5 (TUP5) gene of Arabidopsis
(Arabidopsis thaliana) encoding an acetylornithine aminotransferase (ACOAT),
catalyzing the fourth step of arginine biosynthesis. The free arginine content
was strongly reduced in the chemically induced recessive mutant tup5-1, root
growth was restored by supplementation with arginine and its metabolic
precursors, and a yeast (Saccharomyces cerevisiae) ACOAT mutant was
complemented by TUP5. Two null alleles of TUP5 caused a reduced viability of
gametes and embryo lethality, possibly caused by insufficient Arg supply from
maternal tissue. TUP5 expression is positively regulated by light, and a
TUP5-green fluorescent protein was localized in chloroplasts. tup5-1 has a
unique light-dependent short root phenotype. Roots of light-grown tup5-1
seedlings switch from indeterminate growth to determinate growth with
arresting cell production and an exhausted root apical meristem. The
inhibitory activity was specific for blue light, and the inhibiting light was
perceived by the root. Thus, tup5-1 reveals a novel role of amino acids and
blue light in regulating root meristem function
