Data di Pubblicazione:
2012
Citazione:
STUDY OF LOW PHYTIC ACID 1 LOCUS IN MAIZE / F. Cerino Badone ; relatore: S. R. Pilu ; correlatori: G. A. Sacchi, E. Cassani ; coordinatore: D. Bassi. Universita' degli Studi di Milano, 2012 Jan 24. 24. ciclo, Anno Accademico 2011. [10.13130/cerino-badone-francesco_phd2012-01-24].
Abstract:
Phytic acid (myo-inositol-1,2,3,4,5,6-hexakisphosphate; InsP6) is ubiquitous in eukaryotic cells and constitutes the major storage form of phosphate in plant seeds (from 60% to 80%). During maturation it is accumulated in the protein storage vacuole in inclusions called globoids; the phosphate groups present in phytic acid (PA) are able to form phytate salts (phytin) binding important mineral cations. In mature maize kernels, 80% of PA is localized in the scutellum and the remaining 20% in the aleurone layer. The phosphorus stored as PA is remobilized during germination by phytase enzymes: these are also found in many microorganisms.
Regarding the involvement of P in agricultural production and its sustainability, it has been estimated that nearly 50% of elemental P used yearly in global agricultural activities is accumulated in the PA.
PA forming mixed salts with mineral cations is mainly excreted by monogastric animals and humans because they do not have phytase activity in their digestive systems. Considering that seeds are an important component of animal feed and human food, the limitations of phosphorus and micronutrients bioavailability imply a decrease in their nutritional value. Furthermore the undigested phosphorous contained in excreted phytin can contribute to water pollution (eutrophication).
These negative effects have led to breeding programmes which have the aim of reducing the PA content in the seeds of several cultivated plants. The main way to reach this result by conventional breeding is the isolation of low phytic acid (lpa) mutations, capable of restraining the biosynthesis or the storage of PA in the seed; the increased P and mineral cation bioavailability in lpa seeds is confirmed by nutritional trials.
In maize three low phytic acid mutants have been isolated: lpa1 and lpa2 by chemical mutagenesis, lpa3 by transposon tagging. Compared to the other mutations in maize, lpa1 exhibited the major reduction of PA in the seed, this comes with a proportional increase of free P without changing the total P content. Taking advantage of this property, lpa mutants can be recognized by the HIP (high inorganic phosphate) phenotype of the seeds. The Lpa1 gene encodes for ZmMRP4 (accession number EF586878) a multidrug-associated-protein (MRP) belonging to the subfamily of ATP-binding cassette (ABC) transmembrane transporters. MRP proteins are implicated in different roles like the transport of organic ions and anthocyanins, detoxification of xenobiotic compounds, transpiration control, and tolerance to oxidative stress. The role of this MRP protein is not completely understood but it is fundamental for phytic acid accumulation and viability of seeds. low phytic acid mutants isolated in rice and soybean are related to defects in homologues of the maize ABC transporter.
It was observed that lpa mutations found in several crops usually bring pleiotropic effects on plant and seed performance, such as reduced germination and emergence rate, lower seed filling, weakening in stress resistance. The presence of pleiotropic effects shows that lpa mutations influence not only the seed but also the whole plant and its production. This can reflect the relevance of inositol phosphates as multifunctioning molecules, and their involvement in fundamental signaling and developmental pathways, like DNA repair, RNA editing, chromatin remodeling and control of gene expression. Furthermore phytic acid exhibits, by its ability to chelate iron, a potent antioxidant activity, avoiding the formation of reactive oxygen species.
With the aim to isolate new maize low phytic acid mutants mutagenesis treatment were performed with EMS (ethyl-methanesulfonate). Since wild type mature maize seeds contain high amount of phytic phosphate an
Tipologia IRIS:
Tesi di dottorato
Keywords:
maize ; low phytic acid ; mutagenesis ; multi-drug-resistance (MRP) protein ; inositol phosphates ; ATP-binding cassette (ABC) transporter ; 5-Azacytidine treatment ; gene silencing ; paramutation ; anthocyanin transporter ; Colored1 gene
Elenco autori:
F. CERINO BADONE
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