Biochemical and genetic analyses of N metabolism in maize testcross seedlings: 1. Leaves |
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Authors: | Ignacio Trucillo Silva Hari Kishan R. Abbaraju Lynne P. Fallis Hongjun Liu Michael Lee Kanwarpal S. Dhugga |
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Affiliation: | 1.Department of Agronomy,Iowa State University,Ames,USA;2.Trait Discovery and Technology,DuPont Pioneer,Johnston,USA;3.AVX Corporation,Fountain Inn,USA;4.Department of Genetics, Developmental and Cell Biology,Iowa State University,Ames,USA;5.State Key Laboratory of Crop Biology,Shandong Agricultural University,Tai’an,China;6.International Center for Maize and Wheat Improvement (CIMMYT),El Batan,Mexico |
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Abstract: | Key messageAside from the identification of 32 QTL for N metabolism in the seedling leaves of a maize testcross population, alanine aminotransferase was found to be a central enzyme in N assimilation.AbstractExcessive application of nitrogen (N) fertilizer to grow commercial crops like maize is a cause of concern because of the runoff of excess N into streams and rivers. Breeding maize with improved N use efficiency (NUE) would reduce environmental pollution as well as input costs for the farmers. An understanding of the genetics underlying N metabolism is key to breeding for NUE. From a set of 176 testcrosses derived from the maize IBMsyn10 population grown in hydroponics, we analyzed the youngest fully expanded leaf at four-leaf stage for enzymes and metabolites related to N metabolism. Three enzymes, along with one metabolite explained 24% of the variation in shoot dry mass. Alanine aminotransferase (AlaAT) stood out as the key enzyme in maintaining the cellular level of glutamate as it alone explained 58% of the variation in this amino acid. Linkage mapping revealed 32 quantitative trait loci (QTL), all trans to the genomic positions of the structural genes for various enzymes of N assimilation. The QTL models for different traits accounted for 7–31% of the genetic variance, whereas epistasis was generally not significant. Five coding regions underlying 1-LOD QTL confidence intervals were identified for further validation studies. Our results provide evidence for the key role of AlaAT in N assimilation likely through homeostatic control of glutamate levels in the leaf cells. The two QTL identified for this enzyme would help to select desirable recombinants for improved N assimilation. |
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