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 Nacetyl-c-aminobutyraldehyde (NAGABald) with a Km of approximately 10 mM and moderate affinity towards c-guanidinobutyraldehyde (GGBald) and betaine aldehyde (bet-ald) with Km values of approximately 260 lM and 63 lM respectively. A lower Km of approximately 9 lM was observed with c-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 lM 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.

Identification of aroma volatiles and understanding 2-acetyl-1-pyrroline biosynthetic mechanism in aromatic mung bean (Vigna radiata (L.) Wilczek)

“…As per their reports, non-functionality of BADH2 leads in the accumulation of GABald/D 1 -pyrroline which non-enzymatically reacts with MG to form 2AP (Bradbury et al 2008;Chen et al 2008;Kaikavoosi et al 2015). MG is derived from dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (G3P) in the glycolytic pathway (Phillips and Thornalley 1993).…”

Understanding the Fragrance in Rice

“…The non-functional badh2 (encoded by recessive bad2) result in AB-ald accumulation followed with the increment in the concentration of 2AP in scented rice. Bradbury et al [42] suggested that γ-aminobutyraldehyde (GABald) is an effective substrate for BADH2 and that accumulation and spontaneous cyclisation of GABald to form Δ 1 -pyrroline due to a non-functional BADH2 enzyme as the likely cause of 2AP accumulation in rice. However, in another study, increased expression of Δ 1 -pyrroline-5-carboxylate synthetase in fragrant varieties compared with non-fragrant varieties, as well as associated elevated concentrations of its product, led to the conclusion that Δ 1 -pyrroline-5-carboxylate, usually the immediate precursor of proline synthesized from glutamate, reacts directly with methylglyoxal to form 2AP [43], with no direct role proposed for BADH2.…”

Variations of Growth Parameters in Some Aromatic Rice Verities under Salt Stress

“…As a result, efforts are being undertaken in many countries to increase the production of this type of rice. There are evidences showing that the aromatic quality of these rice varieties varies depending upon the areas and locality of the rice cultivation (Bradbury et al 2008;Hossain et al 2008;Nagarajan et al 2010). …”