水稻早衰突变体psls1的基因定位及克隆

水稻叶片早衰直接影响作物的光合效率,减少产量,降低品质。深入研究早衰的分子机制对控制和延缓衰老具有重要意义。本文报道了一个早衰突变体psls1(premature senescence leaf with spots)的基因定位及克隆结果。突变体在发育到七叶期以后,叶片自下而上叶绿素含量下降,过氧化氢过量积累,突变体叶片逐渐黄化至枯萎;其他农艺性状如株高、分蘖数、主穗长、结实率和穗粒数也相应变差。电镜观察进一步发现,psls1衰老叶片中叶绿体降解、类囊体基粒片层模糊,嗜锇颗粒明显增多。遗传分析表明,psls1受1对隐性基因控制,利用psls1×IRAT129杂交组合F2分离群体中的1690个早衰个体,将基因PSLS1定位在第7染色体分子标记ZS-3和ZS-8之间89 kb的范围内。测序研究发现,区间内一个编码铁氧还依赖的谷氨酸合酶基因LOC_Os07g46460的第2外显子末位的G被替换为A,导致转录本的错误剪切,突变体的c DNA缺失了57 bp碱基片段。在突变体中该基因表达量下降,谷氨酸合酶活性降低,其产物谷氨酸含量显著下降、其他氨基酸代谢紊乱。水培低氮处理下可诱发突变体psls1早衰。研究结果表明,由于PSLS1突变使得谷氨酸合酶失活,氮代谢异常而导致突变体psls1早衰。

Gene Mapping and Cloning of a Premature Leaf Senescence Mutant psls1 in Rice

Leaf early senescence directly reduces its photosynthetic capacity, decreasing crop yield and grain quality. It is of great importance to identify novel mutants and characterize their molecular and physiological mechanisms. In this paper, we reported gene mapping and cloning of a psls1 mutant (premature senescence leaf with spots) in rice. The mutant showed early senescence symptoms, including decreased chlorophyll content, over-accumulated H₂O₂, yellow-withered leaf and increased dead cell from bottom to top of plant after the 7-leaf stage. Moreover, the plant height, tiller number, panicle length, and the number of grains per panicle were significantly lower in psls1. We observedthe degradation of chloroplast, unclean thylakoid and numerous osmiophilic granules in psls1 leavesby transmission electron microscope (TEM). Genetic analysis demonstrated that the phenotype of psls1 was determined by a single recessive gene. Using genetic population derived from psls1 × IRAT129, the psls1 locus was mapped in a 89 kb region flanked by markers zs-3 and zs-8 on chromosome 7, containing 12 putative open reading frames (ORFs). Sequence analysis revealed a single-base substitution occurred in the genomic sequence of LOC_Os07g46460, which led to a 59 bp deletion in its cDNA, and therefore, predicted LOC_Os07g46460 (PSLS1), encoding a ferredoxin-dependent glutamate synthase as the candidate gene. The mRNA expression level of mutated PSLS1 decreased sharply, resulting in reduction of glutamate synthase activity and abnormal amino acid metabolism in psls1. Under low nitrogen treatment, the senescence phenotype of psls1 could occur as early as at the 3-leaf stage. These results indicated that psls1 senescence phenotype might be associated with the loss of glutamate synthase activity and the abnormal amino acid metabolism.