芥菜种子颜色调控基因TT8的等位变异及其地理分布分析

Allelic variation and geographical distribution of TT8 for seed color in Brassica juncea Czern. et Coss.

在芸薹属植物中TT8基因是种子颜色的调控基因。异源四倍体芥菜TT8基因有2个拷贝,分别位于A09与B08染色体上。本研究针对不同拷贝设计特异引物,对749份芥菜进行扩增、测序或酶切检测,发现BjuA09.TT8和BjuB08.TT8各有7个和6个等位变异。与野生型相比, BjuA09.TT8.a1-a5和BjuB08.TT8.b1-b4等位基因都发生了大片段插入,而BjuA09.TT8.a6出现了删除,但BjuB08.TT8.b5仅在第7外显子处有1个碱基替换。使用Repeatmasker软件对等位基因序列与甘蓝型油菜注释库进行重复序列比对,发现BjuA09.TT8.a1-a4和BjuB08.TT8.b1-b4等位基因主要含有Ⅰ类转座子,少量为Ⅱ类转座子及Helitron类转座子插入。统计还发现, BjuA09.TT8.a4-BjuB08.TT8.b5单倍型为主要的黄籽单倍型,占所分析黄籽材料的89.49%(247/276),其次为BjuA09.TT8.a4-BjuB08.TT8.b3单倍型,占6.52%。地理分布分析结果显示,中国尤其是新疆芥菜黄籽突变等位基因频率显著高于世界其他地区,这与历史记载相印证,说明芥菜黄籽性状可能起源于中国新疆。本研究结果为油菜黄籽育种选用优异基因资源提供了依据。

The gene TT8 regulates seed color in Brassica species. Two TT8 copies, designated as BjuA09.TT8 and Bju B08.TT8,were cloned from the chromosomes A09 and B08 of the allotetraploid B. juncea, which had 7 and 6 alleles in worldwide 749 B.juncea accessions, respectively. Compared with the wild type, BjuA09.TT8.a1-a5 and BjuB08.TT8.b1-b4 alleles carried large insertions, while BjuA09.TT8.a6 and Bju B08.TT8.b5 had a deletion and a base substitution at exon 7, respectively. Comparison of the allele sequences with the annotated library of swede rapeseed(B. napus) using the software Repeatmasker revealed that BjuA09.TT8.a1-a4 and Bju B08.TT8.b1-b4 alleles contained class Ⅰ transposons, a few class Ⅱ transposons, and Helitron-like transposon insertions. The haplotype analysis showed that BjuA09.TT8.a4–BjuB08.TT8.b5 was the major yellow seed haplotype,accounting for 89.49%(247/276) of the yellow seed accessions detected, followed by the haplotype BjuA09.TT8.a4–BjuB08.TT8.b3, amounting for 6.52%. Analysis of geographical origin of yellow seed accessions revealed that there were had a higher frequency of yellow seed mutation especially in Xinjiang region, China, than the other parts of the world, suggesting possible origin of yellow seed mustard in Xinjiang, China together with historical records. This study provides a basis for the selection of superior genetic resources for breeding yellow seed rapeseed.