The Low Phytic Acid Phenotype in Soybean Line CX1834 Is Due to Mutations in Two Homologs of the Maize Low Phytic Acid Gene

Plant seeds accumulate phosphorus in the form of myo-inositol1,2,3,4,5,6-hexa-kisphosphate, commonly referred to as phytic acid. Phytic acid is found complexed with cationic mineral species in the form of phytate, which is not well digested or absorbed by monogastric species such as humans, poultry, and swine. As a result, soybean [Glycine max (L.) Merr.] has an effective defi ciency of phosphorus and other minerals, despite high levels of minerals and phosphorus in the seed. Excreted phytate can also contribute to phosphorus contamination of groundwater and eutrophication of freshwater lakes and streams. In maize (Zea mays L. ssp. mays), a recessive mutation in a conserved region within the low phytic acid 1 (lpa1) gene is responsible for the low phytic acid phenotype. We have identifi ed recessive mutations in two soybean homologs of the maize lpa1 gene in soybean line CX1834, a mutagenized line with a low phytic acid phenotype. In three populations analyzed, we identifi ed complete association between homozygosity for mutant alleles of the two lpa1 homologs and the low phytic acid phenotype in soybean. Molecular marker assays were designed that can be used to directly select for the mutant alleles that control the phenotype. PLANT SEEDS ACCUMULATE phosphorus in the form of myo-inositol-1,2,3,4,5,6-hexa-kisphosphate, which is found complexed with mixed cationic species. Th is storage form of phosphorus is commonly referred to as phytate. Th e vast majority of phosphorus in the seed is found in the form of phytate (65–85%), which can account for up to 1 to 3% of soybean seed composition (Bilyeu et al., 2008; Raboy, 2002). Although phytate is effi ciently mobilized in germinating seedlings, it is not well digested or absorbed when consumed by monogastric species such as humans, poultry, and swine. Because phytate is found complexed with mineral cations, soybean [Glycine max (L.) Merr.] has an eff ective defi ciency of phosphorus and other minerals, despite high levels of minerals and phosphorus in the meal (Raboy, 2007). In addition, excreted phytate can contribute to phosphorus contamination of groundwater and eutrophication of freshwater lakes and streams (Corell, 1989; Raboy, 2007). While plants synthesize phytic acid as a phosphorus storage mechanism, it has been demonstrated that a reduction in phytic acid accumulation in seeds can be accomplished without major negative consequences to plant performance (Bilyeu et al., 2008; Shi et al., 2007; Spear and Fehr, 2007). Published in The Plant Genome 2:179–190. Published 10 July 2009. doi: 10.3835/plantgenome2008.03.0013 © Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA An open-access publication All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. J.D. Gillman and K. Bilyeu, USDA-ARS, Univ. of Missouri-Columbia, 110 Waters Hall, Columbia, MO 65211; V.R. Pantalone, Dep. of Plant Sciences, 2431 Joe Johnson Dr., Univ. of Tennessee, Knoxville, TN 37996-4561. Mention of a trademark, vendor, or proprietary product does not constitute a guarantee or warranty of the product by the USDA and does not imply its approval to the exclusion of other products or vendors that may also be suitable. Received 21 Jan. 2009. *Corresponding author ([email protected]). Abbreviations: ABC, ATP-binding cassette; chr, chromosome; LG, linkage group; lpa1, low phytic acid 1; MIPS, myo-inositol phosphate synthase; MRP, multidrug resistance protein; NIL, near-isogenic line; PCR, polymerase chain reaction; QTL, quantitative trait loci; RIL, recombinant inbred line; SNP, single nucleotide polymorphism; SSR, simple sequence repeat; W82, ‘Williams 82’. Published July, 2009