Proceedings of the XLVI Italian Society of Agricultural Genetics - SIGA Annual Congress

Giardini Naxos, Italy - 18/21 September, 2002

ISBN 88-900622-3-1

Poster Abstract - 4.11

Genetic, biochemical and molecular characterization of lpa 241, a mutation that confers a decreased phytic acid and an increased free phosphate content in maize seed tissues

PILU R.*, PANZERI D.*, CONSONNI G.*, RASMUSSEN S.**, GAVAZZI G.*, NIELSEN E.***

*) Dipartimento di Produzione Vegetale (Di.Pro.Ve.), Università degli Studi di Milano, Via Celoria 2, 20133 Milano

salvatore.pilu@unimi.it

**) Department of Plant Biology and Biogeochemistry , RISO National Laboratory, DK-4000 Roskilde Denmark

soren.rasmussen@risoe.dk

***) Dipartimento di Genetica e Microbiologia, Università di Pavia, Via Ferrata 1, 27100 Pavia

nielsen@ipvgen.unipv.it

maize, mutagenesis, phytic acid, RT-PCR

Grain crops typically contain about 10 mg phytic acid (myo-inositol-1,2,3,4,5,6-hexakisphospate or Ins P6) per seed dry weight, representing about 65% to 90% of seed total P (Raboy 1990, 1997). Once synthesised, most phytic acid P is deposited as a mixed “phytate” or “phytin” salt of potassium and magnesium, although phytates contain addition other mineral cations such as iron and zinc (Lott 1984). These salts are packaged into discrete, membrane-bound inclusions referred to as globoids. In the cereal grains essentially all phytates are localised in the embryo and aleurone tissues (O’Dell et al 1972). In maize greater than 80% is found in the embryo with the remainder in the aleurone. In wheat, barley, rice and other small grains the reverse is observed. During germination phytate salts are broken down by action of phytases, releasing their P, mineral and myo-inositol content that are then used by the growing seedling (Labourè et al 1993). Phytic acid is poorly digest by monogastric animals and is considered to be antinutritional factor in animals fed rations that contain it and so the reduction or elimination of these compounds in seeds is attractive breeding target. The biochemical pathway to phytic acid can be subdivided in two parts: the early “Ins-supply” pathway followed by an ins phosphate/Ptd Ins-phosphate pathway that convert ins to InsP6. With a few important exceptions, a great deal of progress as been made in the molecular genetics of these pathways, particularly in mammalian systems and yeast, little progress has been made at the molecular level in plants. The only known synthetic source of the ins ring is the activity of the enzyme D-myo-Inositol(3)P1 synthase (MIPS), that converts glucose 6-P to D-Ins(3)P1 (Loewus and Murthy2000).there seems to be a close relationship between the biosynthesis of phytic acid and the formation of D-myo-inositol-3-phosphate by MIPS.

Recessive maize mutants with decreased grain phytic acid content have been isolated by Raboy’s group in U.S.A (Raboy et al. 2000). Most of the mutations isolated this turned out to perturb embryo or aleurone development. However, the recessive mutation named lpa 241 (low phytic acid 241) we isolated in maize following chemical mutagenesis shows about 90% reduction of phytic acid, with a relevant increase of seed free ortophosphate content and no associated negative effects on embryo development. The results of the genetic, biochemical and molecular characterization carried out by SSR mapping, MDD-HPLC and RT-PCR are consistent with a mutation affecting the activity of MIPS1S gene, the first enzyme of phytine biosynthetic path.