Peptide-Bound Methionine Sulfoxide (MetO) Levels and MsrB2 Abundance Are Differentially Regulated during the Desiccation Phase in Contrasted Acer Seeds

Abstract

Norway maple and sycamore produce desiccation-tolerant (orthodox) and desiccation-sensitive (recalcitrant) seeds, respectively. Drying affects reduction and oxidation (redox) status in seeds. Oxidation of methionine to methionine sulfoxide (MetO) and reduction via methionine sulfoxide reductases (Msrs) have never been investigated in relation to seed desiccation tolerance. MetO levels and the abundance of Msrs were investigated in relation to levels of reactive oxygen species (ROS) such as hydrogen peroxide, superoxide anion radical and hydroxyl radical (•OH), and the levels of ascorbate and glutathione redox couples in gradually dried seeds. Peptide-bound MetO levels were positively correlated with ROS concentrations in the orthodox seeds. In particular, •OH affected MetO levels as well as the abundance of MsrB2 solely in the embryonic axes of Norway maple seeds. In this species, MsrB2 was present in oxidized and reduced forms, and the latter was favored by reduced glutathione and ascorbic acid. In contrast, sycamore seeds accumulated higher ROS levels. Additionally, MsrB2 was oxidized in sycamore throughout dehydration. In this context, the three elements •OH level, MetO content and MsrB2 abundance, linked together uniquely to Norway maple seeds, might be considered important players of the redox network associated with desiccation tolerance.

Localization and Dynamics of the Methionine Sulfoxide Reductases MsrB1 and MsrB2 in Beech Seeds

“…The first plant gene encoding methionine sulfoxide reductase B (MsrB) was identified in Arabidopsis while researchers were searching for homologs to the human selenoprotein X proteins [ 37 ]. Since that study was published, numerous studies have shown that MsrB enzymes are important factors involved in the regulation of multiple processes during plant development [ 28 , 29 ] as well as in the response to biotic and abiotic stress [ 23 , 24 , 25 , 29 ]. Châtelain et al [ 29 ] determined that the Msr repair system plays a decisive role in establishing and preserving seed longevity.…”

“…In particular, the abundance of MsrB2 correlates well with the time of storage, suggesting that this Msr isoform is important in maintaining seed quality during long-term storage. Moreover, it has recently been reported that the MsrB2 protein is involved in seed desiccation tolerance [ 28 ]. Importantly, the loss of desiccation tolerance also results in the loss of seed viability [ 38 ].…”

“…These isoforms were determined to be MsrB1, MsrB2, and MsrA4, but the latter exhibited considerably lower activity [ 23 , 40 ]. Interestingly, both beech seeds and Acer seeds [ 28 ] accumulate these proteins in cells lacking chloroplasts. Our microscopic analysis showed that MsrB1/B2 are present in several types of cells in both embryonic axes and cotyledons.…”

“…Proteins were separated by SDS-PAGE on 12% polyacrylamide gels, with an equal amount of protein (20 μg) in each lane ( Figure S6 ). Western blot analysis was performed according to the method described by Wojciechowska et al [ 28 ]. Primary antibodies against MsrB1 and MsrB2 [ 20 ] were diluted 1:1000 in 5% skimmed milk.…”

“…The majority of research has focused on investigating the role of Msr in the stress response and for both abiotic [ 23 , 24 ], and biotic [ 25 , 26 ] stresses. Moreover, an increasing number of studies have suggested that Msrs may participate in developmental processes, including seed maturation [ 27 ], seed desiccation [ 28 ], seed longevity [ 29 ], and senescence and maturation of fruits [ 30 , 31 ].…”