title: Inactivation of an aminoaldehyde dehydrogenase is responsible for fragrance in rice.
abstract: Rice (Oryza sativa) has two betaine aldehyde dehydrogenase homologs, BAD1 and BAD2, encoded on chromosome four and chromosome eight respectively. BAD2 is responsible for the characteristic aroma of fragrant rice. Complementary DNA clones of both BAD1 and BAD2 were isolated and expressed in E. coli. BAD2 had optimum activity at pH 10, little to no affinity towards N-acetyl-gamma-aminobutyraldehyde (NAGABald) with a Km of approximately 10 mM and moderate affinity towards gamma-guanidinobutyraldehyde (GGBald) and betaine aldehyde (bet-ald) with Km values of approximately 260 microM and 63 microM respectively. A lower Km of approximately 9 microM was observed with gamma-aminobutyraldehyde (GABald), suggesting BAD2 has a higher affinity towards this substate in vivo. The enzyme encoded on chromosome four, BAD1, had optimum activity at pH 9.5, showed little to no affinity towards bet-ald with a Km of 3 mM and had moderate affinity towards GGBald, NAGABald and GABald with Km values of approximately 545, 420 and 497 microM respectively. BAD1 had a half life roughly double that of BAD2. We discuss the implications of these findings on the pathway of fragrance generation in Basmati and Jasmine rice and the potential of rice to accumulate the osmoprotectant glycine betaine.
authors.affiliation: Centre for Plant Conservation Genetics, Southern Cross University, Military Road, Lismore, NSW 2480, Australia.
authors.forename: Louis M T
authors.initials: LM
authors.lastname: Bradbury
authors.forename: Susan A
authors.initials: SA
authors.lastname: Gillies
authors.forename: Donald J
authors.initials: DJ
authors.lastname: Brushett
authors.forename: Daniel L E
authors.initials: DL
authors.lastname: Waters
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Henry
mesh_terms: D050728:Betaine-Aldehyde Dehydrogenase / Q000302:isolation & purification / Q000378:metabolism*; D004789:Enzyme Activation; D004926:Escherichia coli; D006207:Half-Life; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D012275:Oryza / Q000201:enzymology* / Q000502:physiology*; D010940:Plant Proteins / Q000302:isolation & purification / Q000378:metabolism; D011392:Proline / Q000737:chemistry; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D013379:Substrate Specificity; D013696:Temperature
chemical_list: D010940:Plant Proteins; D011994:Recombinant Proteins; D011392:Proline; D050728:Betaine-Aldehyde Dehydrogenase