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

Abstract

Beech seeds are produced irregularly, and there is a need for long-term storage of these seeds for forest management practices. Accumulated reactive oxygen species broadly oxidize molecules, including amino acids, such as methionine, thereby contributing to decreased seed viability. Methionine oxidation can be reversed by the activity of methionine sulfoxide reductases (Msrs), which are enzymes involved in the regulation of many developmental processes and stress responses. Two types of Msrs, MsrB1 and MsrB2, were investigated in beech seeds to determine their abundance and localization. MsrB1 and MsrB2 were detected in the cortical cells and the outer area of the vascular cylinder of the embryonic axes as well as in the epidermis and parenchyma cells of cotyledons. The abundances of MsrB1 and MsrB2 decreased during long-term storage. Ultrastructural analyses have demonstrated the accumulation of these proteins in protein storage vacuoles and in the cytoplasm, especially in close proximity to the cell membrane. In silico predictions of possible Msr interactions supported our findings. In this study, we investigate the contribution of MsrB1 and MsrB2 locations in the regulation of seed viability and suggest that MsrB2 is linked with the longevity of beech seeds via association with proper utilization of storage material.

Are Methionine Sulfoxide-Containing Proteins Related to Seed Longevity? A Case Study of Arabidopsis thaliana Dry Mature Seeds Using Cyanogen Bromide Attack and Two-Dimensional-Diagonal Electrophoresis

“…In this context, MetO might induce structural changes in 12S seed storage proteins, and could interfere with their packaging during seed maturation and their mobilization during seed germination. Importantly, these changes might be reversible, because MSRs were recently immunolocalized in PSVs [41]. Among the MetO-containing proteins identified in our study (Table 1), protein disulfide isomerase conferring redox homeostasis and Elongation factor 1 playing a role in protein expression, were identified as being altered in MsrA and MsrB1 mutants of human embryonic kidney cells, respectively, exposed to oxidative stress [23].…”

“…Consistent with a role in aging [30,41], several recent studies have pointed out the role of protein oxidation in seed longevity, notably including oxidation at Met residues in proteins [42][43][44]. To further document this question and toward a global characterization of oxidation of Met residues in proteins to MetO, we have developed a handy proteomic method called 2Dd-CNBr based on the use of two-dimensional diagonal electrophoresis (2Dd) and cyanogen bromide (CNBr) cleavage after the first dimension [45], followed by mass spectrometry for the identification of proteins of interest.…”

“…Met sulfoxide and MSRs are known to play roles in these pathways. For example, the role of the MSR system was demonstrated to affect seed longevity in Medicago truncatula, Arabidopsis [30] and Fagus sylvatica [41]. Recently, it was revealed that the abundance of MSRB2 was related to seed desiccation tolerance [60].…”

Recent progress in molecular genetics and omics-driven research in seed biology

“…This reaction can be reversed through the specific action of methionine sulfoxide reductases (MSR) [223]. Importantly, the MSR system has been shown to control seed longevity in Medicago, Arabidopsis [224], and Fagus sylvatica [225]. Then, a more severe oxidative attack of Met results in the irreversible formation of a sulfone derivative (Met sulfone).…”

“…Moreover, this study disclosed the presence of MetO in Arabidopsis 12S globulins, which could indicate that, like carbonylation, MetO might induce structural changes in seed storage proteins and could interfere with their packaging during seed maturation and their mobilization during seed germination. Importantly, these changes might be reversible because MSRs were recently immunolocalized in protein storage vacuoles where SSPs are stored during seed maturation [225].…”