Rice OsLHT1 Functions in Leaf-to-Panicle Nitrogen Allocation for Grain Yield and Quality

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.

Targeting Nitrogen Metabolism and Transport Processes to Improve Plant Nitrogen Use Efficiency

“…Root importers for amino acids include amino acid permeases AAP1 and AAP5, proline transporter ProT2, and lysine-histidine-type transporters LHT1 and LHT6 (Grallath et al, 2005 ; Hirner et al, 2006 ; Lee et al, 2007 ; Svennerstam et al, 2007 , 2008 , 2011 ; Lehmann et al, 2011 ; Perchlik et al, 2014 ; Ganeteg et al, 2017 ; Wang et al, 2019 ; Guo et al, 2020a , b ), and their importance for plant growth has been demonstrated (Tegeder and Masclaux-Daubresse, 2018 ; Guo et al, 2020a ). In rice, constitutive overexpression of OsAAP1 led to increased N uptake and reallocation, positively affecting tiller number and final grain yield ( Figure 1 ; Ji et al, 2020 ).…”

l-Aspartate: An Essential Metabolite for Plant Growth and Stress Acclimation

“…AtUCP1 and AtUCP2 have sequence similarity of about 72%; however, they differ significantly in their specific activity, making AtUCP1 more active in the transport of Asp/Glu than AtUCP2 [51]. Additionally, a recent report shows that the knockout of lysine-histidine-type transporter 1 (OsLHT1) in rice affected root uptake of Asp, which eventually impaired the nitrogen translocation to the shoot, suggesting that OsLHT1 could possibly be an Asp transporter as well [55]. Despite several putative Asp membrane transporters identified to date in different genome databases, their transport capabilities in plants are yet to be investigated.…”

Recent Advances on Nitrogen Use Efficiency in Rice

“…Based on gene-based genetic association analysis of aspartate uptake between japonica and indica rice subspecies, Lysine-Histidine-type Transporter 1 (OsLHT1) was identified as a candidate gene [66]. OsLHT1 is expressed throughout the root and in the leaf, and oslht1 mutants showed the reduced amino acids root uptake and allocation from root to shoot, thereby growth inhibition and low yield [66][67][68]. Plasma membrane-localized OsProT1 and OsProT3 function to specifically mediate transport of Pro and GABA in yeast and showed differential expression patterns [69].…”