Abstract
Proper allocation of nitrogen (N) from source leaves to grains is essential step for high crop grain yield and N use efficiency. In rice (Oryza sativa) grown in flooding paddy field, amino acids are the major N compounds for N distribution and re-allocation. We have recently identified that Lysine-Histidine-type Transporter 1 (OsLHT1) is the major transporter for root uptake and root-to-shoot allocation of amino acids in rice. In this study, we planted knockout mutant lines of OsLHT1 together wild-type (WT) in paddy field for evaluating OsLHT1 function in N redistribution and grain production. OsLHT1 is expressed in vascular bundles of leaves, rachis, and flowering organs. Oslht1 plants showed lower panicle length and seed setting rate, especially lower grain number per panicle and total grain weight. The concentrations of both total N and free amino acids in the flag leaf were similar at anthesis between Oslht1 lines and WT while significantly higher in the mutants than WT at maturation. The Oslht1 seeds contained higher proteins and most of the essential free amino acids, similar total starch but less amylose with lower paste viscosity than WT seeds. The mutant seeds showed lower germination rate than WT. Knockout of OsLHT1 decreased N uptake efficiency and physiological utilization efficiency (kg-grains/kg-N) by about 55% and 72%, respectively. Taken together, we conclude that OsLHT1 plays critical role in the translocation of amino acids from vegetative to reproductive organs for grain yield and quality of nutrition and functionality.
Highlights
In natural soil ecosystem, nitrogen (N) is presented in diversity forms including both inorganic and organic N (Rasmussen et al, 2010; Robertson and Groffman, 2015)
Since the leaf I and developing panicles are growing organs and need large amount of nitrogenous compounds transported via stem from leaves (Muhammad and Kumazawa, 1974), the abundant expression of OsLHT1 in leaves and rachis hints that OsLHT1 may play a role in leaf-to-panicle amino acid allocation
The promoter-GUS assay in rice indicated that OsLHT1 is localized in the leaf blade, especially in the cells of the major and minor veins (Guo et al, 2020)
Summary
Nitrogen (N) is presented in diversity forms including both inorganic and organic N (Rasmussen et al, 2010; Robertson and Groffman, 2015). Rice (Oryza sativa) is commonly grown in flooding paddy filed where ammonium is dominant form of inorganic N (Xu et al, 2012). The N is highly distributed to both the flag leaves and panicles (Muhammad and Kumazawa, 1974; Itoh et al, 2005). During grain-filling stage, the N supplied for panicles is mainly redistributed from leaves and about 70% of N can be transported into the panicle (Muhammad and Kumazawa, 1974).
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