Melatonin improves the tolerance of plants to various environmental stresses by protecting plant cells against oxidative stress damage. The objective of the current study was to determine whether exogenous melatonin (MT) treatments could help protecting peanut (Arachis hypogaea) seedlings against salinity stress. This was achieved by investigating enzymatic and non-enzymatic antioxidant systems and the expression of melatonin biosynthesis related genes in response to salinity stress with or without exogenous MT. The results showed a significant increase in the concentrations of reactive oxygen species (ROS) in peanut seedlings under salinity stress. The exogenous application of melatonin decreased the levels of ROS through the activation of antioxidant enzymes in peanut seedlings under salinity stress. Transcription levels of melatonin biosynthesis related genes such as N-acetylserotonin methyltransferase (ASMT1, ASMT2, ASMT3), tryptophan decarboxylase (TDC), and tryptamine 5-hydroxylase (T5H) were up-regulated with a 150 µM melatonin treatment under salinity stress. The results indicated that melatonin regulated the redox homeostasis by its ability to induce either enzymatic or non-enzymatic antioxidant systems. In addition, phylogenetic analysis of melatonin biosynthesis genes (ASMT1, ASMT2, ASMT3, TDC, T5H) were performed on a total of 56 sequences belonging to various plant species including five new sequences extracted from Arachis hypogaea (A. hypogaea). This was based on pairwise comparison among aligned nucleotides and predicted amino acids as well as on substitution rates, and phylogenetic inference. The analyzed sequences were heterogeneous and the A. hypogaea accessions were primarily closest to those of Manihot esculenta, but this needs further clarification.

A detailed study of putative recombination events and their evolution frequency in the whole genome of the currently known members of the family Tombusviridae, comprising 79 accessions retrieved from the international databases, was carried out by using the RECCO and RDP version 3.31β algorithms. The first program allowed the detection of potential recombination sites in seven out of eight virus genera (Aureusvirus, Avenavirus, Carmovirus, Dianthovirus, Necrovirus, Panicovirus, and Tombusvirus), the second program provided the same results except for genus Dianthovirus. On the other hand, both methods failed to detect recombination breakpoints in the genome of members of genus Machlomovirus. Furthermore, based on Fisher's Exact Test of Neutrality, positive selection exerted on protein-coding genes was detected in 17 accession pairs involving 15 different lineages. Except genera Machlomovirus, and Panicovirus along with unclassified Tombusviridae, all the other taxonomical genera and the unassigned Tombusviridae encompassed representatives under positive selection. The evolutionary history of all members of the Tombusviridae family showed that they segregated into eight distinct groups corresponding to the eight genera which constitute this family. The inferred phylogeny reshuffled the classification currently adopted by the International Committee on Taxonomy of Viruses. A reclassification was proposed.