Abstract
In plants, myo-inositol-1,2,3,4,5,6-hexakisphosphate (InsP6), also known as phytic acid (PA), is a major component of organic phosphorus (P), and accounts for up to 85% of the total P in seeds. In rice (Oryza sativa L.), PA mainly accumulates in rice bran, and chelates mineral cations, resulting in mineral deficiencies among brown rice consumers. Therefore, considerable efforts have been focused on the development of low PA (LPA) rice cultivars. In this study, we performed genetic and molecular analyses of OsLpa1, a major PA biosynthesis gene, in Sanggol, a low PA mutant variety developed via chemical mutagenesis of Ilpum rice cultivar. Genetic segregation and sequencing analyses revealed that a recessive allele, lpa1-3, at the OsLpa1 locus (Os02g0819400) was responsible for a significant reduction in seed PA content in Sanggol. The lpa1-3 gene harboured a point mutation (C623T) in the fourth exon of the predicted coding region, resulting in threonine (Thr) to isoleucine (Ile) amino acidsubstitution at position 208 (Thr208Ile). Three-dimensional analysis of Lpa1 protein structure indicated that myo-inositol 3-monophosphate [Ins(3)P1] could bind to the active site of Lpa1, with ATP as a cofactor for catalysis. Furthermore, the presence of Thr208 in the loop adjacent to the entry site of the binding pocket suggests that Thr208Ile substitution is involved in regulating enzyme activity via phosphorylation. Therefore, we propose that Thr208Ile substitution in lpa1-3 reduces Lpa1 enzyme activity in Sanggol, resulting in reduced PA biosynthesis.
Highlights
In most cereal crops, myo-inositol-1,2,3,4,5,6-hexakisphosphate (InsP6), known as phytic acid (PA), is considered a major source of phosphorus (P) available in the form of phytate, and accounts for 65–85% of the total P in seeds [1]
No significant differences were observed between mutant and wild type in morphological characteristics, such as secondary internodal length, grain length, grain width, panicle length, and spikelet fertility (Fig 1B and Fig 1C). These data indicate that a low PA mutant, Sanggol shows poor agronomic performance with respect to the flowering time, yield, and yield components compared with the wild type, Ilpum
Several genes controlling PA biosynthesis have been reported in major crop plants [13, 20, 25, 28, 48,49,50]
Summary
Myo-inositol-1,2,3,4,5,6-hexakisphosphate (InsP6), known as phytic acid (PA), is considered a major source of phosphorus (P) available in the form of phytate, and accounts for 65–85% of the total P in seeds [1].
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