Transcriptomic Analysis of Helianthus annuus Roots at the Early Stage of Resistance to Orobanche cumana

Orobanche cumana is a root alloparasitic plant that drastically reduces Helianthus annuus (sunflower) production. In this study, transcriptomic changes of O. cumana resistant (HZ2399) and O. cumana sensitive (SQ25) sunflower seedlings were investigated at six time points (0-72 h) following O. cumana infection. The process of resistance to O. cumana was similar in HZ2399 and SQ25 seedlings, however, significantly higher regulatory activity was observed in the resistant plants. In HZ2399, most of the 54 upregulated genes were involved in phenylpropanoid biosynthesis, plant-pathogen interaction, and plant hormone signal transduction pathways. These genes were mainly associated with antioxidant responses, responses to stress, stimulation responses, and metabolic processes. The expression level of the three most significantly upregulated genes in HZ2399 (4CL2, EDS1, and TGA3) was significantly higher than that of SQ25 suggesting that they may be the main causes of O. cumana immunity in HZ2399. It is hypothesized that sunflower resistance to O. cumana parasitism is dependent on salicylic acid, a disease resistance protein (TIR-NBS-LRR class) family (RPS4), and EDS1. The results of this study contributes to elucidating the mechanism of O. cumana resistance in sunflower and for the molecular breeding of O. cumana resistance.