Polyol/Monosaccharide Transporters (PLTs/PMTs) localized in the plasma membrane have previously been identified in plants. The physiological role and the functional properties of these proteins in legume plants are, however, unclear. Here we describe the functional analysis of LjPLT1, a plasma membrane-localized PLT protein from Lotus japonicus. The LjPLT1 gene was strongly expressed in the vascular tissue of roots, stems and leaves. Expression of the LjPLT1 cDNAs in yeast revealed that the protein functions as a broad-spectrum H⁺ -symporter for both linear polyols of sorbitol and mannitol, and cyclic polyol myo-inositol. It also catalyzes the transport of different hexoses, including fructose, glucose, galactose and mannose. Overexpression of LjPLT1 (OELjPLT1) results in inhibition of plant growth and a decrease in nodule nitrogenase activity in L. japonicus. The soluble sugars were increased in newly expanded leaves, roots and nodules but decreased in mature leaves in OELjPLT1 plants. In addition, the OELjPLT1 seedlings displayed an increased sensitivity to high content mannitol and boron toxicity, but neither drought nor salinity stresses. Taken together, the present study indicates that the LjPLT1 protein may participate in the translocation of hexoses/polyols to regulate multiple physiological and growth processes in L. japonicus.

先前已在植物中鉴定出位于质膜中的多元醇/单糖转运蛋白（PLT/PMT）。然而，这些蛋白质在豆科植物中的生理作用和功能特性尚不清楚。在这里，我们描述了 LjPLT1 的功能分析，LjPLT1 是一种来自百脉根的质膜定位 PLT 蛋白。LjPLT1基因在根、茎、叶的维管组织中强表达。LjPLT1 cDNA 在酵母中的表达表明，该蛋白作为山梨醇和甘露醇的线性多元醇以及环状多元醇肌醇的广谱 H ^{+同向转运蛋白。}它还催化不同己糖的转运，包括果糖、葡萄糖、半乳糖和甘露糖。LjPLT1 ( OELjPLT1 )的过度表达会导致L. japonicus植物生长受到抑制并降低根瘤固氮酶活性。OELjPLT1植物新展开的叶、根和根瘤中可溶性糖增加，但成熟叶中可溶性糖减少。此外，OELjPLT1幼苗对高含量甘露醇和硼毒性的敏感性增加，但对干旱和盐胁迫均不敏感。综上所述，本研究表明，LjPLT1蛋白可能参与己糖/多元醇的易位，以调节日本乳杆菌的多种生理和生长过程。