Rhizobia cystathionine γ-lyase-derived H2S delays nodule senescence in soybean.

Hydrogen sulphide (H2S) is required for optimal establishment of soybean (Glycine max)-Sinorhizobium fredii symbiotic interaction, yet its role in regulating the nitrogen fixation-senescence transition remains poorly understood. A S. fredii cystathionine γ-lyase (CSE) mutant deficient in H2S synthesis showed early nodule senescence characterized by reduced nitrogenase activity, structural changes in nodule cells, and accelerated bacteroid death. In parallel, the CSE mutant facilitated the generation of reactive oxygen species (ROS) and elicited antioxidant responses. We observed that H2S-mediated persulfidation of cysteine C31/C80 in ascorbate peroxidase (APX) and C32 in APX2 modulated enzyme activity, thereby participating in hydrogen peroxide (H2O2) detoxification and delaying nodule senescence. Comparative transcriptomic analysis revealed a significant up-regulation of GmMYB128, an MYB transcription factor (TF), in the CSE mutant nodules. Functional analysis through overexpression and RNAi lines of GmMYB128 demonstrated its role as a positive regulator in nodule senescence. MYB128-OE inoculated with the CSE mutant strain exhibited a reduction in nitrogenase activity and a significant increase in DD15 expression, both of which were mitigated by NaHS addition. Changes at the protein level encompassed the activation of plant defenses alongside turnover in carbohydrates and amino acids. Our results suggest that H2S plays an important role in maintaining efficient symbiosis and preventing premature senescence of soybean nodules.

A preliminary genetic distinctness of four Coilia fishes (Clupeiformes: Engraulidae) inferred from mitochondrial DNA sequences.

In order to understand the genetic distinctness between four Coilia fishes,i.e., C. ectenes, C. e. taihuensis, C. mystus, and C. grayii, the combined cytochrome b (cytb), 12S rRNA and 16S rRNA gene sequences were obtained and analysed. The results are as follows: 1) neighbour-joining (NJ) and maximum parsimony (MP) trees were built with 1000 bootstrap replicates. They supported that Coilia fishes consisted of two clades: C. grayii form a monophyletic group, and the rest samples form the other monophyletic group; 2) the topological differences between the NJ tree and the MP tree are checked by Templeton test, indicating that their differences are insignificant (P > 0.05); and 3) Kimura-2-parameter distances between the samples of C. ectenes, C. e. taihuensis and C. mystus are all no bigger than 1.6%, and most of them are between 0.0% and 0.9%. C. ectenes, C. e. taihuensis and C. mystus are closely related and that their differences may be under subspecies.