Integrative analysis based on transcriptome revealed the relation of auxin to turnip hypocotyl-tuber formation

Turnip (Brassica campestris L. ssp. rapifera Matag syn. B. rapa L.) is characterized by bulbous hypocotyl-tuber, which is an important agronomic trait of the Brassica plants, but the molecular mechanism underlying the development of turnip hypocotyl-tuber has rarely been explored. Contrary to turnip, pak-choi (B. campestris L. ssp. chinensis Makino syn. B. rapa ssp. chinensis) is characterized by small and long hypocotyl. Based on the difference in morphological and anatomical characteristics of hypocotyl between turnip and pak-choi at different developmental stages, integrative analysis was performed in this study. Comparative transcriptomic analysis demonstrated that the changes of expression patterns of genes related to plant hormones especially auxin in hypocotyl were closely related to turnip hypocotyl enlargement at the early stages (8 and 32 days after sowing). The immunolocalization of auxin during early hypocotyl development stages also showed auxin signal differ-ences in secondary xylem of hypocotyl between the two subspecies, and further 1-Naphthaleneacetic acid (NAA) treatments confirmed the effect of auxin in turnip hypocotyl-tuber formation. Our study provided valuable in-formation for further exploration of the role of auxin underlying turnip hypocotyl enlargement, enabling a more comprehensive understanding of plant storage organ development.

Automated summary

This study investigated the molecular mechanism underlying the development of turnip hypocotyl-tuber. Comparative transcriptomic analysis revealed that changes in the expression patterns of genes related to plant hormones, especially auxin, were closely related to turnip hypocotyl enlargement. The localization of auxin during early hypocotyl development stages also exhibited differences between turnip and pak-choi subspecies. These findings contribute to a better understanding of auxin's role in turnip hypocotyl enlargement.