Molecular hydrogen can take part in phytohormone signal pathways in wild rice

Molecular hydrogen (H₂) could be a novel signal in phytohormone signaling pathways in response to biotic and abiotic stresses. Here, we employed two wild rice species (Oryza rufipogon Griff. and O. minuta J. Presl) to test this hypothesis using hydrogen-rich water (HW). The expression differences of phytohormone and hydrogenase genes between conventional rice (Oryza sativa L,) and wild rice were determined by real-time quantitative polymerase chain reaction, and the effects of HW on gene expression of wild rice were detected during three growth stages. Expression of hydrogenase genes, synthesis genes, and receptor genes of salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) signalling pathways was higher in six wild rice types than in conventional rice. Hydrogen-rich water up-regulated expression of two hydrogenase genes, SA, JA, and ET receptor genes and synthesis genes in the seedling stage of wild rice. But this positive regulation by HW was less significant in the vegetative and reproductive stages.     

Exogenous Melatonin Modulates Endogenous H2S Homeostasis and L-Cysteine Desulfhydrase Activity in Salt-Stressed Tomato (Solanum lycopersicum L. var. cherry) Seedling Cotyledons

Although melatonin has been reported to function as a stress signaling molecule, not much information is available on the biochemical and molecular events associated with probable melatonin-hydrogen sulfide crosstalk in plants. Present work provides evidence on the role of melatonin in the modulation of H₂S homoeostasis during NaCl stress in dark-grown tomato (Solanum lycopersicum L. var. cherry) seedlings. NaCl stress (120 mM) inhibits hypocotyl elongation, promotes primary root growth and enhances electrolytic leakage from tomato seedlings. Treatment with H₂S donor (100 µM; NaHS) tends to reverse these effects, all the more so (additive effect) in the presence of melatonin. NaCl stress and exogenous melatonin (30 µM) treatments modulate endogenous H₂S accumulation and positively upregulate the activity of L-cysteine desulfhydrase (L-DES; EC 4.4.1.15; cytosolic). Melatonin has been observed to temporally modulate the activity of specific isoforms of H₂S biosynthesizing enzyme, L-DES in seedling cotyledons. Zymographic analysis of L-DES isoforms in tomato seedling cotyledons has provided novel findings in plant system. Melatonin treatment decreases H₂S accumulation in NaCl-stressed seedling cotyledons which is accompanied by a contrasting increase in L-DES activity. Melatonin, therefore, regulates endogenous H₂S concentration in seedling cotyledons (NaCl treated), thus indicating the role of H₂S catabolism pathways in H₂S homoeostasis. Present findings thus reveal that exogenous melatonin modulates early H₂S signaling in cotyledons of tomato seedlings subjected to NaCl stress. Furthermore, exogenous melatonin and H₂S in combination (additive effect) ameliorate NaCl stress-induced growth changes in tomato seedlings.

     

Downregulation of OsPK1 Contributes to Oxidative Stress and the Variations in ABA/GA Balance in Rice

Abscisic acid (ABA) is a phytohormone that aids plants in coping with stress conditions. ABA and gibberellin (GA) are hormone partners that function via a complicated and antagonistic network. In ospk1, a dwarf rice mutant, the contents of ABA in the youngest leaf sheaths of 6-week-old seedlings and the uppermost internodes of heading stage plants were both increased, and the synthesis of bioactive GAs was suppressed, which may disharmonize ABA/GA balance. In ospk1, expression of three putative enzyme genes related to stress response was upregulated. A strong browning symptom was observed in the second internode (Int2, counted from the top) and part of panicles of ospk1 at the late productive phase. Furthermore, higher levels of H₂O₂ in flag leaf and Int2 were observed in ospk1 than those in wild type. These data suggest that ospk1 may undergo certain stress, especially oxidative stress. Here, we provide evidences that the downregulation of OsPK1 (a cytosolic pyruvate kinase) in ospk1 mutant results in variations in ABA/GA balance in rice and contributes to oxidative stress, which provide a new clue for understanding the connection of pyruvate kinase, ABA/GA balance, and oxidative stress in rice.     

Biochemical and molecular changes induced by salinity stress in <Emphasis Type="Italic">Oryza sativa</Emphasis> L.

Salinity stress constrains the growth, development, and yield in crops. Rice is an important cereal crop highly affected by salinity. To ensure the agriculture production in salt-affected soils, it is enormously entail to understand the salt adaptation strategies of plants. Salinity directly affects the morphology, physiology, and metabolism of the plants. The current study was carried out to check the influence of different concentrations of sodium chloride on rice cultivar. Higher concentration of the NaCl showed significant reduction in the growth, pigment system, and metabolites in rice cultivars. Salinity also elicited the antioxidant enzymes (CAT, SOD, and POX) response and gene expression. Cell biological studies showed the H₂O₂ production and nuclear fragmentation due to alleviated salinity stress. To delineate the portrayal of antioxidant proteins and autophagy mechanism in salinity stress, the homologs of rice CAT1, Mn-SOD, GPX, ATG1, and ATG6 genes were retrieved from blast search. The real-time PCR analysis showed differential expression of genes and depicts new molecular insight of target genes to understand the salinity stress and autophagy-mediated stress signaling pathways.     

MAPKs as a cross point in H2O2 and auxin signaling under combined cadmium and zinc stress in rice roots

Previously, we have reported the role of MAPKs (mitogen-activated protein kinases) under cadmium stress. This work continue to explore the relationship between MAPKs, H₂O₂, auxin signaling, and OsHMA and OsZIP gene expression in rice (Oryza sativa L.) roots under combined cadmium (Cd) and zinc (Zn) stress. Compared with Cd, Cd+Zn reduced Cd levels but increased Zn accumulation in the roots. Three OsMAPK genes were negatively regulated, while two OsHMA and two OsZIP genes were positively regulated by MAPK pathways under Cd+Zn stress. Transgenic rice expressing DR5-GUS exhibited enhanced GUS activity in H₂O₂-, PD (MAPKK inhibitor PD98059)-, or (Cd+Zn)-treated roots, which also exhibited increased H₂O₂ concentrations, whereas GUS staining decreased in roots in response to Cd+Zn+PD, DMTU (N,N′-dimethylthiourea, a H₂O₂ scavenger), or Cd+Zn+DMTU treatment, with reduced H₂O₂ levels. GUS levels were consistent with H₂O₂ levels, suggesting that MAPK pathway-mediated auxin redistribution occurs via H₂O₂, and H₂O₂ functions downstream of MAPK but upstream of auxin signaling pathways. Furthermore, MAPK pathways serve specific functions in regulating the expression of some key genes of auxin signaling (OsYUCCA, OsPIN, OsARF, and OsIAA) under Cd+Zn stress. Overall, MAPK cascades function in the integration of metal transport, H₂O₂ generation, and auxin signaling in rice seedlings grown under Cd+Zn stress.     

Genomic and metagenomic surveys of hydrogenase distribution indicate H2 is a widely utilised energy source for microbial growth and survival

Recent physiological and ecological studies have challenged the long-held belief that microbial metabolism of molecular hydrogen (H₂) is a niche process. To gain a broader insight into the importance of microbial H₂ metabolism, we comprehensively surveyed the genomic and metagenomic distribution of hydrogenases, the reversible enzymes that catalyse the oxidation and evolution of H₂. The protein sequences of 3286 non-redundant putative hydrogenases were curated from publicly available databases. These metalloenzymes were classified into multiple groups based on (1) amino acid sequence phylogeny, (2) metal-binding motifs, (3) predicted genetic organisation and (4) reported biochemical characteristics. Four groups (22 subgroups) of [NiFe]-hydrogenase, three groups (6 subtypes) of [FeFe]-hydrogenases and a small group of [Fe]-hydrogenases were identified. We predict that this hydrogenase diversity supports H₂-based respiration, fermentation and carbon fixation processes in both oxic and anoxic environments, in addition to various H₂-sensing, electron-bifurcation and energy-conversion mechanisms. Hydrogenase-encoding genes were identified in 51 bacterial and archaeal phyla, suggesting strong pressure for both vertical and lateral acquisition. Furthermore, hydrogenase genes could be recovered from diverse terrestrial, aquatic and host-associated metagenomes in varying proportions, indicating a broad ecological distribution and utilisation. Oxygen content (pO₂) appears to be a central factor driving the phylum- and ecosystem-level distribution of these genes. In addition to compounding evidence that H₂ was the first electron donor for life, our analysis suggests that the great diversification of hydrogenases has enabled H₂ metabolism to sustain the growth or survival of microorganisms in a wide range of ecosystems to the present day. This work also provides a comprehensive expanded system for classifying hydrogenases and identifies new prospects for investigating H₂ metabolism.     

东乡野生稻苗期响应低温胁迫的转录组分析

为了解东乡野生稻（Oryza rufipogon）对低温胁迫的响应机制,对苗期的RNA-seq转录表达谱进行了研究。结果表明,与对照相比,共检测到10 200个差异表达基因（DEGs）,其中5 201个上调表达,4 999个下调表达,其中有426个DEGs位于已报道的水稻耐冷QTL区间,且37个为耐冷调控相关的家族基因。GO功能分类和KEGG代谢路径分析表明,核酸结合转录因子活性、氨基酸生物合成以及光合作用代谢等均参与响应低温胁迫过程。实时荧光定量分析表明,ABA响应蛋白基因、MYB转录因子和40S核糖体蛋白SA基因等12个可能与低温胁迫响应相关的DEGs表达模式与RNA-seq的一致。可见,植物激素传导途径和转录因子相关调控基因在东乡野生稻苗期响应低温胁迫过程中起重要作用。