| The exploitation of low phytic acid (Ipa) crops has widely been considered as an effective strategy to improve the nutritional quality of cereal crops and also solve some environmental problems related to phosphorus pollution. However, the concomitant effects of sharply lowering grain phytic acid (PA) of Ipa crops on their agronomic performance and environmental growth adaptation have not fully understood yet. lpa rice was used in this study to identify its stress adaptation and its relation to spikelet sterility, to investigate the response of PA accumulation and related genes expression to external phosphorus and carbon/nitrogen regulation, using controlled temperature facilities, hydroponics and detached rice panicle culture technique. Moreover, mips-RNAi and mips-overexpressed transgenic lines were also screened to further identify PA metabolism on the molecular level. The main results are as follows:1.Three rice lpa lines and their corresponding wild-types were used to compare their differences in grain PA in response to high temperature (HT) and its relation to spikelet sterility and grain weight at a controlled temperature at filling stage. Results showed that HT caused an increase in grain PA and inorganic phosphate contents, with more substantially rising PA content for Ipa lines compared with corresponding wild-types. This increase in PA content in high temperature-ripened grains was not simply attributed to the reduction in grain weight and relatively enhanced proportion of aleurone layer fraction to whole grains, due to significant increase in PA contents was also detected in milled rice. Moreover, spikelet sterility and grain plumpness of Ipa lines were more susceptible to HT stress than those of wild-types. Exogenous PA spraying with an appropriate concentration could increase grain PA content, but it had only slight contribution to the enhancement of heat tolerance and injurious alleviation for rice exposed to stressful HT.2. myo-inositol-3-phosphate synthase (MIPS) catalyzes the first step, also a rate-limiting step, in PA synthesis. A binary-vector of pTCK303-RiOsMIPS and over-express vector pTCK303-OeOsMIPS were constructed and then transformed into Nipponbare callus mediated by EHA105. Results showed that pTCK303-RiOsMIPS and pTCK303-OeOsMIPS have been integrated into the genome of transgenic plants in To generation, and showed with a3:1genetic separation way in T1transgenic rice population, with the validation of Hyg PCR amplifying analysis. The qRT-PCR results showed that MIPS gene expressions in rice grains showed down-regulation (48.5%) and up-regulation (34.2%) in RNAi transgenic plants and over-express transgenic plants, which was consistent with the change of grain PA concentration in transgenic rice plants (36.9%decrease for RNAi line and28.5%increase for OE line). Grain protein and amylose contents were also changed along with grain PA. Moreover, HT treatment increased grain RINO1and other PA related genes expressions, indicating up-regulation of RINO1(MIPS) gene under HT is one reason for grain PA increase.3. lpa and two japonica rice genotypes were used to investigate the effects of phosphorus (P) treatments on grain PA and its relation to inositol phosphate-related genes expression profiles using hydroponics and detached rice panicle culture technique. Results showed that high P level caused a significant increase in grain PA, inorganic P (Pi) and total P contents. However, grain weight and PA content per grain were P concentration-dependent, and decreased under high P treatment (12P). High P supply decreased grain Zn and Fe concentrations, and their bio-availabilities. Moreover, P treatment also influenced all four PA related genes expression (RINO1, ITP5/6K-6, IPK2and IPK1), with more substantial for RIN01. Specifically, RI0N1gene expression was up-regulated at optimum P (3P) concentration, but was significantly down-regulated with high P treatment (12P), which corresponded with the variation of grain PA content in rice, suggesting RION1was a key metabolic gene in PA synthesis with P supply. In contrast, only a slight contribution of IPK2gene was exhibited in PA synthesis induced by P supply.4. Two japonica rice cultivars were used to investigate the effects of sucrose (C) and glutamine (N) treatments on grain PA and their relations to inositol phosphate-related genes expression profiles using a detached rice panicle culture system. Results showed that high C or N levels caused a significant decrease in grain PA content, with C regulation showed in a more significant way. Leaf removal treatment in the field experiment showed similar results. Moreover, C, N treatments influenced all five PA related genes expression (RIN01, ITP5/6K-6, IPK2, IPK1and MRP), although the variation patterns were varied with filling stages. The down-regulation of RIN01, ITP5/6K-6, IPK1and MRP was probably a main reason for the decrease of PA concentration with exogenous C supply. |
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