Molecular mechanisms of flowering time differentiation revealed by transcriptomic sequencing and de novo analysis in Chinese invasive populations of Ambrosia artemisiifolia.

Background: Ambrosia artemisiifolia is a highly invasive herb with deleterious effects on public health and agricultural systems. Flowering time in this species has been reported to vary along a latitudinal gradient, which may contribute to local adaptation and invasion success in China. However, the molecular basis for the flowering time differentiation remains unclear.

Results: A common garden experiment confirmed a latitudinal gradient in flowering time among seven Chinese populations. Differentially expressed genes (DEGs) across sampling times and flowering time groups were identified through transcriptome sequencing and analyses of DGE and WGCNA, and were partially annotated to circadian rhythm, light response and hormone response through GO enrichment. By annotating to Flowering Interactive Database (FLOR-ID) and protein-protein interaction (PPI) databases, 53 candidate genes for flowering time differentiation were identified, with 23 of these genes linked to the photoperiod pathway. Additionally, 43 of 53 candidate genes exhibited expression correlated with latitude. Six genes, including FKF1, FT, FUL, MAF2, WNK4 and WNK5, were inferred to promote flowering, while 5 genes, FBH3, FLK, NCL(1), POL2A, and ZHD4, likely repress flowering, based on their expression patterns in relation to latitude and sampling times. Notably, NCL(1), FBH3, MAF2, and FLK may function differently in A. artemisiifolia compared to Arabidopsis thaliana.

Conclusions: This study identified key candidate genes related to the differentiation of flowering time in Chinese ragweed populations, providing valuable insights into molecular mechanisms of phenological adaptation and invasive success of ragweed.