Induction of phytic acid synthesis by abscisic acid in suspension-cultured cells of rice

Abstract

A pathway of phytic acid (PA) synthesis in plants has been revealed via investigations of low phytic acid mutants. However, the regulation of this pathway is not well understood because it is difficult to control the environments of cells in the seeds, where PA is mainly synthesized. We modified a rice suspension culture system in order to study the regulation of PA synthesis. Rice cells cultured with abscisic acid (ABA) accumulate PA at higher levels than cells cultured without ABA, and PA accumulation levels increase with ABA concentration. On the other hand, higher concentrations of sucrose or inorganic phosphorus do not affect PA accumulation. Mutations in the genes RINO1, OsMIK, OsIPK1 and OsLPA1 have each been reported to confer low phytic acid phenotypes in seeds. Each of these genes is upregulated in cells cultured with ABA. OsITPK4 and OsITPK6 are upregulated in cells cultured with ABA and in developing seeds. These results suggest that the regulation of PA synthesis is similar between developing seeds and cells in this suspension culture system. This system will be a powerful tool for elucidating the regulation of PA synthesis.

Hormonal Regulation and Expression Profiles of Wheat Genes Involved during Phytic Acid Biosynthesis Pathway

“…Overall, our studies indicated that some of the PA pathway genes are highly induced by ABA when compared to GA 3 . These observations are in accordance with the previous observations reported from rice suspension cells where overall induction of PA biosynthesis genes was observed in presence of ABA [ 14 ]. Altogether, our observations also support that, ABA and GA 3 act antagonistically in developing wheat grains.…”

“…In ABA treated wheat seeds, the expression of TaIPK2 was consistently up-regulated at all time points which are in contrast to the expression of AtIPK2β that decreased upon ABA treatment [ 54 ]. Expression pattern of OsIPK1 [ 14 ], and our results regarding TaIPK1 suggested higher fold accumulation of their transcripts when treated with ABA. Except for TaITPK2 and TaIMP all the wheat genes involved in PA biosynthesis were induced by ABA ( Figure 2 ).…”

“…These observations suggested the important role of PA pathway genes in increments of phytic acid upon exogenous ABA treatment. Enhanced PA accumulation was reported in rice suspension cells when exposed to ABA [ 14 ]. We speculate that upon ABA treatment PA accumulation could be due to the reduced breakdown of PA or its altered transport.…”

“…It has been demonstrated that ABA signal transduction is mediated by inositol-1,4,5-triphosphate (IP 3 ) which, in turn, regulates seed maturation [ 13 ]. Studies have shown a positive correlation between ABA concentration and PA accumulation using seed suspension cells [ 14 ]. During the early phase of wheat seed development, 14 DAA aleurone was found to be present as distinct tissue from endosperm [ 15 ], and it has been reported previously that aleurone tissue is a major site for PA accumulation in most of the cereal grains [ 16 ].…”

“…One IPK1 has been characterized from rice ( OsIPK1 ), Arabidopsis ( AtIPK1 ) and wheat ( TaIPK1 ) [ 6 , 23 , 34 ]. In order to understand the regulation of PA pathway genes, especially in seeds, the effect of hormones was studied previously in rice [ 14 ]. Earlier, it has been shown that the wheat MIPS gene, which is involved in earlier steps of PA biosynthesis, is inducible by ABA, salicylic acid (SA) and other abiotic stresses [ 35 ].…”