Integration of MsrB1 and MsrB2 in the Redox Network during the Development of Orthodox and Recalcitrant Acer Seeds

Abstract

Two related tree species, Norway maple (Acer platanoides L.) and sycamore (Acer pseudoplatanus L.), produce desiccation-tolerant (orthodox) and desiccation-sensitive (recalcitrant) seeds, respectively. We compared the seeds of these two species to characterize the developmentally driven changes in the levels of peptide-bound methionine sulfoxide (MetO) and the abundance of methionine sulfoxide reductases (Msrs) B1 and B2, with respect to the cellular redox environment. Protein oxidation at the Met level was dynamic only in Norway maple seeds, and the reduced MsrB2 form was detected only in this species. Cell redox status, characterized by the levels of reduced and oxidized ascorbate, glutathione, and nicotinamide adenine dinucleotide (NAD)/phosphate (NADP), was clearly more reduced in the Norway maple seeds than in the sycamore seeds. Clear correlations between MetO levels, changes in water content and redox status were reported in orthodox Acer seeds. The abundance of Msrs was correlated in both species with redox determinants, mainly ascorbate and glutathione. Our data suggest that MsrB2 is associated with the acquisition of desiccation tolerance and that ascorbate might be involved in the redox pathway enabling the regeneration of Msr via intermediates that are not known yet.

Involvement of the MetO/Msr System in Two Acer Species That Display Contrasting Characteristics during Germination

“…In sycamore seeds, both MsrB isoforms were detected, notably with an increasing level of MsrB2 in embryonic axes during germination sensu stricto phase (Figure 6). In Norway maple seeds, only one isoform, MsrB2, was detected using western blot analysis as reported during seed maturation [63] and desiccation [64]. The low abundance of MsrB1 in Norway maple seeds might be compensated by MsrB2 or other Msrs including MsrA as reported by Staszak and Pawłowski [56].…”

“…Seeds of Norway maple and sycamore were reported to differ in the levels of ROS, MetO, the abundance of MsrB1 and MsrB2, and the activity of NADPH-dependent reductases during maturation and drying [63,64]. The control of Met redox homeostasis by the MetO/Msr/Met system was proposed to accompany the acquisition of desiccation tolerance in Norway maple seeds [57,64].…”

“…Most available information about their functions relates to their contribution in responses to biotic [89] and abiotic stresses [87,90]. However, these isoforms are also involved in several developmental processes such as seed maturation, desiccation and longevity [63,64].…”

“…The seeds of these two contrasting Acer species were characterized by distinct levels of ROS, MetO, MsrB1 and MsrB2 and differences in the activity of NADPH-dependent reductases during the development and maturation phases [63] as well as during dehydration and desiccation [64]. The MetO/Msr system was assumed to be involved in the establishment of desiccation tolerance in orthodox Norway maple seeds [64].…”

Methionine Sulfoxide Reductase B Regulates the Activity of Ascorbate Peroxidase of Banana Fruit

“…Met oxidation forms two diastereomers of methionine sulfoxide (Met- S -O and Met- R -O), which can be reduced by the methionine sulfoxide reductases, MsrA and MsrB, respectively. Previous studies on Msr have mainly focused on its role in resistance to oxidative stress in organisms [ 21 , 22 , 23 , 24 ], which is related to repair of oxidized proteins, such as GroEL [ 25 ], Fth [ 26 ], hERG [ 27 ], apolipoprotein A-I [ 28 ], CaMKII [ 29 ], TRPM6 channel [ 30 ], HypT [ 31 ], actin [ 32 ], CaM [ 33 , 34 ], GrpEL1/Mge1 [ 35 ], heme oxygenase [ 36 ], and high-density lipoprotein [ 37 ]. Growing evidence suggests that Msr may be implicated in the regulation of protein function by modifying the sulfoxidation of proteins in a similar manner to that of other protein modification, such as phosphorylation [ 38 , 39 , 40 , 41 ].…”