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

Abstract

<p id="C3">The gene<italic> TT8</italic> regulates seed color in <italic>Brassica</italic> species. Two <italic>TT8</italic> copies, designated as <italic>BjuA09.TT8</italic> and <italic>BjuB08.TT8</italic>, were cloned from the chromosomes A09 and B08 of the allotetraploid <italic>B. juncea</italic>, which had 7 and 6 alleles in worldwide 749<italic> B. juncea</italic> accessions, respectively. Compared with the wild type,<italic> BjuA09.TT8.a1-a5</italic> and <italic>BjuB08.TT8.b1-b4</italic> alleles carried large insertions, while <italic>BjuA09.TT8.a6</italic> and <italic>BjuB08.TT8.b5</italic> had a deletion and a base substitution at exon 7, respectively. Comparison of the allele sequences with the annotated library of swede rapeseed (<italic>B. napus</italic>) using the software Repeatmasker revealed that <italic>BjuA09.TT8.a1-a4</italic> and <italic>BjuB08.TT8.b1-b4</italic> alleles contained class I transposons, a few class II transposons, and Helitron-like transposon insertions. The haplotype analysis showed that<italic> BjuA09.TT8.a4-BjuB08.TT8.b5</italic> was the major yellow seed haplotype, accounting for 89.49% (247/276) of the yellow seed accessions detected, followed by the haplotype<italic> BjuA09.TT8.a4- BjuB08.TT8.b3</italic>, 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.