*4.1. Plant Materials*

Two *Brassica rapa* ssp. rapa varieties with different root skin colors (purple turnip 'PT' and green turnip 'GT') were used as plant materials. We collected healthy and consistent purple and green turnips during five consecutive developmental stages, including seedling stage (S1, 15 days after sowing (DAS)), early stage of fleshy root expansion (S2, 30 DAS), full expansion stage of fleshy root (S3, 45 DAS), maturity stage of fleshy root (S4, 55 DAS) and harvest stage of fleshy root (S5, 65 DAS), at the Anningqu experimental site, Xinjiang, China. Plants were grown in natural environment conditions in July 2017 and skin samples were collected from three different plants of each variety (three biological replicates). In total, 30 samples were quickly frozen in liquid nitrogen and stored at −80 ◦C in a refrigerator until further use.
