Mapping of QTLs associated with cytosolic glutamine synthetase and NADH-glutamate synthase in rice (Oryza sativa L.)

Ninety-eight backcross inbred lines (BC₁F₆) developed between Nipponbare, a japonica rice, and Kasalath, an indica rice were employed to detect putative quantitative trait loci (QTLs) associated with the contents of cytosolic glutamine synthetase (GS1; EC 6.3.1.2) and NADH-glutamate synthase (NADH-GOGAT; EC 1.4.1.14) in leaves. Immunoblotting analyses showed transgressive segregations toward lower or greater contents of these enzyme proteins in these backcross inbred lines. Seven chromosomal QTL regions for GS1 protein content and six for NADH-GOGAT protein content were detected. Some of these QTLs were located in QTL regions for various biochemical and physiological traits affected by nitrogen recycling. These findings suggested that the variation in GS1 and NADH-GOGAT protein contents in this population is related to the changes in the rate of nitrogen recycling from senescing organs to developing organs, leading to changes in these physiological traits. Furthermore, a structural gene for GS1 was mapped between two RFLP markers, C560 and C1408, on chromosome 2 and co-located in the QTL region for one-spikelet weight. A QTL region for NADH-GOGAT protein content was detected at the position mapped for the NADH-GOGAT structural gene on chromosome 1. A QTL region for soluble protein content in developing leaves was also detected in this region. Although fine mapping is required to identify individual genes in the future, QTL analysis could be a useful post-genomic tool to study the gene functions for regulation of nitrogen recycling in rice.