Disruption of a Novel NADH-Glutamate Synthase2 Gene Caused Marked Reduction in Spikelet Number of Rice

Abstract

Inorganic ammonium ions are assimilated by a coupled reaction of glutamine synthetase and glutamate synthase (GOGAT). In rice, three genes encoding either ferredoxin (Fd)-GOGAT, NADH-GOGAT1, or NADH-GOGAT2, have been identified. OsNADH-GOGAT2, a newly identified gene, was expressed mainly in fully expanded leaf blades and leaf sheaths. Although the distinct expression profile to OsNADH-GOGAT1, which is mainly detected in root tips, developing leaf blades, and grains, was shown in our previous studies, physiological role of NADH-GOGAT2 is not yet known. Here, we isolated retrotransposon mediated-knockout mutants lacking OsNADH-GOGAT2. In rice grown under paddy field conditions, disruption of the OsNADH-GOGAT2 gene caused a remarkable decrease in spikelet number per panicle associated with a reductions in yield and whole plant biomass, when compared with wild-type (WT) plants. The total nitrogen contents in the senescing leaf blade of the mutants were approximately a half of the WT plants. Expression of this gene was mainly detected in phloem companion cells and phloem parenchyma cells associated with large vascular bundles in fully expanded leaf blades, when the promoter region fused with a β-glucuronidase gene was introduced into the WT rice. These results suggest that the NADH-GOGAT2 is important in the process of glutamine generation in senescing leaves for the remobilization of leaf nitrogen through phloem to the panicle during natural senescence. These results also indicate that other GOGATs, i.e., NADH-GOGAT1 and ferredoxin-GOGAT are not able to compensate the function of NADH-GOGAT2.

Nitrogen Use Efficiency in Rice

“…OsNADH-GOGAT2 is mainly expressed in vascular tissues of mature leaf blades and is important in the process Nitrogen in Agriculture -Updatesof glutamine generation in senescing leaves for the remobilization of leaf nitrogen through phloem to the panicle during natural senescence. OsNADH-GOGAT2 mutants had marked reduction in spikelet number per panicle [62,68].…”

Dry Matter and N Contributions to the Formation of Sink Size in Early- and Late-maturing Rice under Various N Rates in Central China

“…From Kim et al (2010), N is indispensable for the formation of sink size. This was also demonstrated from the evidence that a NADH-glutamate synthase2 gene functions in remobilization of leaf N through phloem to panicle, significantly reduced sink size (Tamura et al, 2011).…”

“…Nitrogen and carbohydrates were taken as the two major factors affecting sink size from the previous studies (Hasegawa et al, 1994;Kamiji et al, 2011;Tamura et al, 2011). Nitrogen application as basal fertilizer or at midtillering increased sink size mainly through more panicles (Table 2), while N application at panicle initiation stage could increase spikelets per panicle (Kamiji et al, 2011).…”

Genome wide analysis and allele mining of diverse sorghum genes involved in nitrogen use efficiency

“…The GOGAT gene, Sobic.003G258800, has been shown to be a major part of the ortho-meta QTL for NUE in cereals (Quraishi et al, 2011). The sorghum GOGAT gene under selection (Sobic.009G225700) belongs to a group including the rice NADH-GOGAT2 gene (Figure 2.3) which has been shown to be involved in spikelet number (Tamura et al, 2011). Rice knock-out mutants for the NADH-GOGAT2 showed a significant decrease of 26-39% in spikelet number per panicle associated with a reduction in yield and plant biomass, as well as total N in senescing leaves (Tamura et al, 2011).…”

“…The sorghum GOGAT gene under selection (Sobic.009G225700) belongs to a group including the rice NADH-GOGAT2 gene (Figure 2.3) which has been shown to be involved in spikelet number (Tamura et al, 2011). Rice knock-out mutants for the NADH-GOGAT2 showed a significant decrease of 26-39% in spikelet number per panicle associated with a reduction in yield and plant biomass, as well as total N in senescing leaves (Tamura et al, 2011). The rice NADH- The expression of Sobic.003G258800 is mainly in both roots and shoots, whereas the expression of Sobic.002G402700 is highest mainly only in shoots.…”