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Nicotinamidase activity is important for germination
Author(s) -
Hunt Lee,
Holdsworth Michael J.,
Gray Julie E.
Publication year - 2007
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/j.1365-313x.2007.03151.x
Subject(s) - germination , biology , nad+ kinase , poly adp ribose polymerase , mutant , dna repair , nicotinamide , biochemistry , enzyme , nicotinamide adenine dinucleotide , arabidopsis , dna , polymerase , gene , botany
Summary It has been suggested that nicotinamide must be degraded during germination; however, the enzyme responsible and its physiological role have not been previously studied. We have identified an Arabidopsis gene, NIC2 , that is expressed at relatively high levels in mature seed, and encodes a nicotinamidase enzyme with homology to yeast and bacterial nicotinamidases. Seed of a knockout mutant, nic2‐1 , had reduced nicotinamidase activity, retarded germination and impaired germination potential. nic2‐1 germination was restored by after‐ripening or moist chilling, but remained hypersensitive to application of nicotinamide or ABA. Nicotinamide is a known inhibitor of NAD‐degrading poly(ADP‐ribose) polymerases (PARP enzymes) that are implicated in DNA repair. We found reduced poly(ADP)ribosylation levels in nic2‐1 seed, which were restored by moist chilling. Furthermore, nic2‐1 seed had elevated levels of NAD, and germination was hypersensitive to methyl methanesulphonate (MMS), suggesting that PARP activity and DNA repair responses were impaired. We suggest that nicotinamide is normally metabolized by NIC2 during moist chilling or after‐ripening, which relieves inhibition of PARP activity and allows DNA repair to occur prior to germination.