Comparative transcriptome analysis provides novel insights into phytohormone dynamic changes during seed germination in carrot (Daucus carota L.)

The germination of carrot seeds is a complex regulatory process and the relationship between phytohormone and carrot seed germination is unclear. We performed morphological observation, transcriptome sequencing, phytohormone content determination, and gene expression profiles analysis. The results showed that the white hypocotyls of carrot seeds grew rapidly on the 3 d, and cotyledons unfold on the 8 d. A total of 745 differentially expressed genes (DEGs) related to plant hormone signal transduction were identified at different germination stages (3, 5, 8 d), and most of the genes were up-regulated obviously in the later stage. The content of GA3 reached its peak on the first day of germination, with a content of 7.12 ng/g FW, and showed a trend of first decreasing, then increasing and decreasing. And the trend of GA4 content change was similar to GA3 content from 2 d to 8 d. The contents of indole-3-acetic acid (IAA) and methyl jasmonate (MeJA) showed a gradual increasing trend, while the content of abscisic acid (ABA) gradually decreased. The results of RT-qPCR showed that DcGA3ox1 and DcAOC expressed decreased, while DcGA20ox2 and DcYUCCA increased in the whole process. These results provide potential new insights for the efficient production of carrots..