Molecular and physiological characterization of two sunflower near-isogenic lines with contrasting haplotypes for...

Leaf senescence is regulated by several genetic mechanisms and environmental factors. During senescence, cellular organelles are degraded and chlorophylls are lost. Concomitantly, macromolecules are broken down into smaller molecules that are transported into tissues like seeds, a process called nutrient remobilization. By reducing photosynthesis and increasing nutrient remobilization, senescence affects seed yield and seed protein. Moreover, its understanding is relevant for agro-ecology, because it could increase nitrogen use efficiency. Sunflower, the fourth oilseed worldwide, is characterized by low water and nitrogen requirements. It shows rapid onset of senescence after anthesis, which hinders its productivity. In this crop, the interaction among senescence, water stress and cover crops for green manure has already been explored from an agronomic perspective. Here, we studied this interaction at the molecular level by comparing morpho-physiological traits and biochemical responses, transcriptome and metabolome of two sunflower near-isogenic lines with contrasting haplotypes for the senescence related LES10.179 QTL. We characterized our plants under water stress and in presence of residues of two cover crops, namely vetch and rye.

The overall response to drought in our findings revealed several novel insights, such as the global decrease of secondary metabolites and the involvement of potentially antioxidant minor compounds. The characterization of the LES10.179 QTL, instead, suggested that senescence was likely controlled by a homolog to NYC1, a gene involved in chlorophyll degradation. The LES10.179 QTL also affected seed protein content: the haplotype associated with early senescence lowered it, the other one acting the opposite way. Cover crops had a minor impact on molecular profiles, and no interactive effects were observed between drought and the LES10.179 QTL.

This is the first characterization of a QTL associated with leaf senescence in sunflower. This QTL has also an impact on seed protein content and it is not affected by drought. Therefore, it could prove especially useful for breeding applications. Anyway, further evidence is needed to precisely state whether the observed stay-green phenotype is functional or cosmetic.