日本冈山大学的研究团队近日宣布，他们成功发现了在水稻进行锰吸收时不可或缺的排出型转运体蛋白OsMTP9。
锰是植物生长所必需的微量营养元素，水稻在生长过程中也需要对这类矿物质进行吸收，而排出型转运体蛋白OsMTP9对水稻的锰吸收有着至关重要的作用。
冈山大学资源植物科学研究所的马建锋教授以及高知大学教育研究综合科学系生命环境医学部的上野大势教授等组成联合科研小组共同完成了此次研究。相关研究成果已于2015年11月9日刊载在知名科学杂志《Nature Plants》上。
植物在光合作用过程中将水分解成氧气，而锰是这一过程不可或缺的微量元素，植物一般是通过根部从土壤中吸收所需要的锰元素。
在以往的研究中，该小组已经成功发现了将锰元素从土壤中摄入根表皮细胞内所需要的转运蛋白OsNramp5，而将细胞内的锰元素通过凯氏转移到中柱向地上部的转运体并未被找到。
Effect of knockout of MTP9 on the growth and yield.: a, Shoot and root growth at the vegetative stage. Seedlings (9-day-old) of both wild-type rice (WT) and two mutants (mtp9-1 and mtp9-2) were cultured in a nutrient solution for 10 days. b–e, Grain yield and fertility at the reproductive stage. Total shoot (straw + grains) dry weight (b), grain yields (c) and fertility (d,e). Wild-type rice (WT) and two independent mutant lines were grown in soil until ripening. Data represent the mean ± s.d. (n = 3–4). Different letters indicate a significant difference (P < 0.05) using Tukey’s test.
Tissue- and cell-specificity of localization of MTP9 in primary and lateral roots.: a–d, Immunostaining of MTP9 protein (red) in primary root of the wild-type rice (a,b) and mtp9-1 mutant (c,d). e–h, Immunostaining of MTP9 protein (red) in the lateral root of the wild-type rice (e,f) and mtp9-1 mutant (g,h). b,d,f,h show magnified images of the yellow box in a,c,e and g, respectively. i,j, Co-immunostaining of MTP9 protein (red) and Nramp5 (green) in the lateral root of wild-type rice. Blue shows cell wall autofluorescence. j shows a magnified image of the yellow box in i. en, endodermis; ex, exodermis; ep, epidermis; sc, sclerenchyma; pe, pericycle; xv, xylem vessel. Scale bars, 100 µm (a,c), 20 µm (e,g,i).
此次发现的OsMTP9与OsNramp5类似，都存在于根部表皮细胞与内皮细胞中。OsNramp5朝向根外部不均匀分布，而OsMTP9则朝向根内侧不均匀分布。当相关遗传基因受损时，水稻对锰元素的吸收和向地上部的转运都会大幅减少，进而导致水稻产量降低。
Subcellular localization of rice MTP9.: a–h, Localization of the GFP–MTP9 fusion protein (a–d), and GFP (e–h), transiently expressed in protoplasts prepared from rice shoots. a,e, GFP image; b,f, chlorophyll fluorescence; c,g, bright field image; and d,h, a combined image of the three channels. Scale bars, 20 µm. i, Double staining of MTP9 and nuclei in lateral root. Red represents signal from the antibody and cyan from DAPI (4′,6-diamidino-2-phenylindole) and cell wall autofluorescence. Arrowhead indicates nucleus stained with DAPI. Scale bar, 20 µm. j, Western blot analysis of MTP9 in membrane fractions prepared by discontinuous sucrose gradient. H+-ATPase and V-ATPase were used as markers of plasma membrane and tonoplast, respectively.
本次研究成功探明了水稻锰元素吸收的转运机制，专家表示将通过进一步开发，探寻提高锰吸收能力的方法，培育出能够在锰元素含量较低的土壤中生长的水稻品种。
