Phytic acid (PA), myo-inositol 1,2,3,4,5,6-hexakisphosphate, is the main storage form of phosphorus in plants. It is localized in seeds, deposited as mixed salts of mineral cations in protein storage vacuoles; during germination, it is hydrolyzed by phytases. When seeds are used as food/feed, PA and the bound cations are poorly bioavailable for human and monogastric livestock due to their lack of phytase activity. Reducing the amount of PA is one strategy to solve these problems and is an objective of genetic improvement for improving the nutritional properties of major crops. In this work, we present data on the isolation of a new maize (Zea mays L.) low phytic acid 1 (lpa1) mutant allele obtained by chemical mutagenesis. This mutant, named lpa1-7, is able to accumulate less phytic phosphorus and a higher level of free inorganic phosphate in the seeds compared with wild type. It exhibits a monogenic recessive inheritance and lethality as homozygous. We demonstrate that in vitro cultivation can overcome lethality allowing the growth of adult plants, and we report data regarding embryo and leaf abnormalities and other defects caused by negative pleiotropic effects of this mutation.

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So far, in maize, three classes of mutants involved in phytic acid biosynthesis have been isolated: lpa1, lpa2 and lpa3. In 2007, a gene tagging experiment performed by Shi et al. found that mutations in ZmMRP4 (multidrug resistance-associated proteins 4) gene cause lpa1 phenotype. In previous studies, we isolated and described a single recessive lpa mutation (originally named lpa241), which was allelic to the lpa1-1 mutant, and was consequently renamed lpa1-241. It showed a decrease in the expression of the myo-inositol (Ins)-3-phosphate synthase gene (mips1S). In this study, we present genetic and molecular analyses of the lpa1-241 mutation that indicate an epigenetic origin of this trait, that is, a paramutagenic interaction that results in meiotically heritable changes in ZmMRP4 gene expression, causing a strong pleiotropic effect on the whole plant. The use of a 5-Azacytidine treatment provided data suggesting an association between gene methylation and the lpa1-241 phenotype. To our knowledge, this is the first report of a paramutagenic activity not involving flavonoid biosynthesis in maize, but regarding a key enzyme of an important metabolic pathway in plants.

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