Abstract
Understanding the genetic basis of nitrogen and carbon metabolism will accelerate the development of plant varieties with high yield and improved nitrogen use efficiency. A robotized platform was used to measure the activities of 10 enzymes from carbon and nitrogen metabolism in the maize (Zea mays) intermated B73 × Mo17 mapping population, which provides almost a 4-fold increase in genetic map distance compared with conventional mapping populations. Seedling/juvenile biomass was included to identify its genetic factors and relationships with enzyme activities. All 10 enzymes showed heritable variation in activity. There were strong positive correlations between activities of different enzymes, indicating that they are coregulated. Negative correlations were detected between biomass and the activity of six enzymes. In total, 73 significant quantitative trait loci (QTL) were found that influence the activity of these 10 enzymes and eight QTL that influence biomass. While some QTL were shared by different enzymes or biomass, we critically evaluated the probability that this may be fortuitous. All enzyme activity QTL were in trans to the known genomic locations of structural genes, except for single cis-QTL for nitrate reductase, Glu dehydrogenase, and shikimate dehydrogenase; the low frequency and low additive magnitude compared with trans-QTL indicate that cis-regulation is relatively unimportant versus trans-regulation. Two-gene epistatic interactions were identified for eight enzymes and for biomass, with three epistatic QTL being shared by two other traits; however, epistasis explained on average only 2.8% of the genetic variance. Overall, this study identifies more QTL at a higher resolution than previous studies of genetic variation in metabolism.
Highlights
Understanding the genetic basis of nitrogen and carbon metabolism will accelerate the development of plant varieties with high yield and improved nitrogen use efficiency
Despite the importance of carbon and nitrogen metabolism, little is known about the genetic variation of activities of enzymes involved in the pathways
Keurentjes et al (2008) investigated transcript quantitative trait loci (QTL), enzyme activity QTL, and metabolite QTL in an Arabidopsis Landsberg erecta 3 Cape Verde Islands recombinant inbred lines (RILs) population and identified examples where the structural gene colocated with transcript QTL and enzyme activity QTL, and other cases where the enzyme activity QTL was unrelated to the position of the structural gene and the genetic variation in the encoding transcript
Summary
Understanding the genetic basis of nitrogen and carbon metabolism will accelerate the development of plant varieties with high yield and improved nitrogen use efficiency. Despite the importance of carbon and nitrogen metabolism, little is known about the genetic variation of activities of enzymes involved in the pathways. In a study of 10 glycolytic enzymes in Arabidopsis (Arabidopsis thaliana), Mitchell-Olds and Pedersen (1998) found significant activity QTL for most of the enzymes, and three QTL mapped very close to known enzyme-encoding loci (e.g. hexokinase, phosphoglucose isomerase, and PGM). They found a QTL that may be a joint regulator of Glc-6-P dehydrogenase, phosphoglucose isomerase, and Glc-6-phosphatase. Keurentjes et al (2008) investigated transcript QTL, enzyme activity QTL, and metabolite QTL in an Arabidopsis Landsberg erecta 3 Cape Verde Islands RIL population and identified examples where the structural gene colocated with transcript QTL and enzyme activity QTL, and other cases where the enzyme activity QTL was unrelated to the position of the structural gene and the genetic variation in the encoding transcript
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