Institute of Crop Science and Nuclear Technology Utilization, Zhejiang Academy of Agricultural Sciences, Hangzhou, 310021, China.
Theor Appl Genet. 2012 Nov;125(7):1413-23. doi: 10.1007/s00122-012-1922-7. Epub 2012 Jun 26.
Phytic acid (myo-inositol 1, 2, 3, 4, 5, 6 hexakisphosphate) is an important constituent of soybean meal. Since phytic acid and its mineral salts (phytates) are almost indigestible for monogastrics, their abundance in grain food/feed causes nutritional and environmental problems; interest in breeding low phytic acid has therefore increased considerably. Based on gene mapping and the characteristics of inositol polyphosphates profile in the seeds of a soybean mutant line Gm-lpa-ZC-2, the soybean ortholog of inositol 1,3,4,5,6 pentakisphosphate (InsP(5)) 2-kinase (IPK1), which transforms InsP(5) into phytic acid, was first hypothesized as the candidate gene responsible for the low phytic acid alteration in Gm-lpa-ZC-2. One IPK1 ortholog (Glyma14g07880, GmIPK1) was then identified in the mapped region on chromosome 14. Sequencing revealed a G → A point mutation in the genomic DNA sequence and the exclusion of the entire fifth exon in the cDNA sequence of GmIPK1 in Gm-lpa-ZC-2 compared with its wild-type progenitor Zhechun No. 3. The excluded exon encodes 37 amino acids that spread across two conserved IPK1 motifs. Furthermore, complete co-segregation of low phytic acid phenotype with the G → A mutation was observed in the F(2) population of ZC-lpa x Zhexiandou No. 4 (a wild-type cultivar). Put together, the G → A point mutation affected the pre-mRNA splicing and resulted in the exclusion of the fifth exon of GmIPK1 which is expected to disrupt the GmIPK1 functionality, leading to low phytic acid level in Gm-lpa-ZC-2. Gm-lpa-ZC-2, would be a good germplasm source in low phytic acid soybean breeding.
植酸（肌醇 1,2,3,4,5,6 六磷酸）是大豆粉的重要组成部分。由于植酸及其矿物质盐（植酸盐）几乎不能被单胃动物消化，因此谷物食品/饲料中丰富的植酸会导致营养和环境问题；因此，人们对培育低植酸的兴趣大大增加。基于基因图谱和大豆突变体品系 Gm-lpa-ZC-2 种子中肌醇多磷酸图谱的特征，推测大豆肌醇 1,3,4,5,6 五磷酸（InsP(5))2-激酶（IPK1）是导致 Gm-lpa-ZC-2 低植酸改变的候选基因，IPK1 将 InsP(5)转化为植酸。随后在 14 号染色体上的映射区域中鉴定出一个 IPK1 直系同源物（Glyma14g07880，GmIPK1）。测序显示，与野生型亲本 Zhechun No.3 相比，Gm-lpa-ZC-2 中的 GmIPK1 基因组 DNA 序列发生了 G → A 点突变，并且 cDNA 序列排除了整个第五外显子。排除的外显子编码横跨两个保守 IPK1 基序的 37 个氨基酸。此外，在 ZC-lpa x Zhexiandou No.4（野生型品种）的 F(2)群体中观察到低植酸表型与 G → A 突变的完全共分离。综上所述，G → A 点突变影响了前体 mRNA 的剪接，导致 GmIPK1 的第五外显子缺失，预计这会破坏 GmIPK1 的功能，导致 Gm-lpa-ZC-2 中的植酸含量降低。Gm-lpa-ZC-2 将成为低植酸大豆育种的良好种质资源。
