Genetic manipulation and quantitative‐trait loci mapping for nitrogen recycling in rice

Abstract

Immunocytological studies in this laboratory have suggested that NADH-dependent glutamate synthase (NADH-GOGAT; EC 1.4.1.14) in developing organs of rice (Oryza sativa L. cv. Sasanishiki) is involved in the utilization of glutamine remobilized from senescing organs through the phloem. Because most of the indica cultivars contained less NADH-GOGAT in their sink organs than japonica cultivars, over-expression of NADH-GOGAT gene from japonica rice was investigated using Kasalath, an indica cultivar. Several T0 transgenic Kasalath lines over-producing NADH-GOGAT under the control of a NADH-GOGAT promoter of Sasanishiki, a japonica rice, showed an increase in grain weight (80% as a maximum), indicating that NADH-GOGAT is indeed a key step for nitrogen utilization and grain filling in rice. A genetic approach using 98 backcross-inbred lines (BC(1)F(6)) developed between Nipponbare (a japonica rice) and Kasalath were employed to detect putative quantitative trait loci (QTLs) associated with the contents of cytosolic glutamine synthetase (GS1; EC 6.3.1.2), which is probably involved in the export of nitrogen from senescing organs and those of NADH-GOGAT. Immunoblotting analyses showed transgressive segregations toward lower or greater contents of these enzyme proteins in these BC(1)F(6). Seven chromosomal QTL regions were detected for GS1 protein content and six for NADH-GOGAT. Some of these QTLs were located in QTL regions for various biochemical and agronomic traits affected by nitrogen recycling. The relationships between the genetic variability of complex agronomic traits and traits for these two enzymes are discussed.

Suppression of glutamate synthase genes significantly affects carbon and nitrogen metabolism in rice (Oryza sativa L.)

“…Limited nitrogen assimilation also affected agronomic characteristics of field-grown plants including yield per plant and thousand kernel weight (Table 2). Other studies have also reported that OsNADH-GOGAT1 affects tiller number and yield per plant [19]. A similar phenotype was reported in glt1-T mutant plants [6].…”

“…In that case, the mRNA level determined by our northern blot analyses would have been out of the range for gene silencing. Yamaya et al [19] also obtained OsNADH-GOGAT1 co-suppressed indica rice using a japonica NADH-GOGAT1 cDNA driven by its own promoter. Only low levels of NADH-GOGAT mRNA accumulated in transgenic tobacco overexpressing alfalfa NADH-GOGAT cDNA, which was detected by RT-PCR analysis at the transcription level rather than by northern blot [18].…”

“…For this purpose, a great deal of research has focused on GS over-expression, with encouraging results reported [17]. Because GOGAT genes are too large to manipulate easily, only a few research results have been reported [18,19]. However, these studies did not systematically analyze how GOGAT genes affect carbon and nitrogen metabolism in vivo.…”

Prospects for Genetic Improvement to Increase Lowland Rice Yields with Less Water and Nitrogen

“…A structure gene for NADH-GOGAT on chromosome 1 was co-located in the QTL region for soluble protein in developing leaves. Yamaya et al (2002) developed transgenic lines overproducing NADH-GOGAT, and two of the transgenic lines showed an increase in grain weight. These studies suggest that genotypes, obtained from genetically manipulated populations or genetic resources, with high GS1 in senescing leaves and high NADH-GOGAT in developing grains should promote N remobilization from straw to grain and consequently improve NUE g (Andrews et al 2004).…”

Identification and Expression Analysis of Glutamine Synthetase Genes in Ramie (Boehmeria nivea L. Gaud)

“…Genetic studies in rice [10][11][12], maize [8,13] and wheat [14] have demonstrated the colocalization of QTLs for GS protein or activity with QTLs in the mapped GS genes that are related to agronomic traits. In higher plants, GS influences and determines the growth and developmental periods of plants, such as the period of grain development and filling in rice [15], wheat [7] and maize [16]; the senescence process in wheat [7]; and the vegetative process in rice and barley [9,17].…”