A New Role for Plastid Thioredoxins in Seed Physiology in Relation to Hormone Regulation

In Arabidopsis seeds, ROS have been shown to be enabling actors of cellular signaling pathways promoting germination, but their accumulation under stress conditions or during aging leads to a decrease in the ability to germinate. Previous biochemical work revealed that a specific class of plastid thioredoxins (Trxs), the y-type Trxs, can fulfill antioxidant functions. Among the ten plastidial Trx isoforms identified in Arabidopsis, Trx y1 mRNA is the most abundant in dry seeds. We hypothesized that Trx y1 and Trx y2 would play an important role in seed physiology as antioxidants. Using reverse genetics, we found important changes in the corresponding Arabidopsis mutant seeds. They display remarkable traits such as increased longevity and higher and faster germination in conditions of reduced water availability or oxidative stress. These phenotypes suggest that Trxs y do not play an antioxidant role in seeds, as further evidenced by no changes in global ROS contents and protein redox status found in the corresponding mutant seeds. Instead, we provide evidence that marker genes of ABA and GAs pathways are perturbed in mutant seeds, together with their sensitivity to specific hormone inhibitors. Altogether, our results suggest that Trxs y function in Arabidopsis seeds is not linked to their previously identified antioxidant roles and reveal a new role for plastid Trxs linked to hormone regulation.