Integrated bioinformatic and physiological analyses reveal the pivotal role of hydrogen sulfide in enhancing low-temperature tolerance in alfalfa.

Hydrogen sulfide (H2 S) is an important gaseous signal molecule that regulates plant growth and stress resistance. However, research on the H2 S synthase (HSase) genes is still limited in the model legume plant Medicago truncatula Gaertn. In the present study, a total of 40 HSase family members were first identified and analyzed in the M. truncatula genome, and these genes distributed across eight chromosomes and were clustered into five groups (I-V) based on their conserved gene structures and protein motifs. Expression analysis revealed that the MtHSase genes were expressed in all the tested abiotic stresses, albeit with expression level differences. This study also showed that H2 S improves low temperature tolerance of alfalfa seedlings by regulating the antioxidant defense system and enhancing photosynthetic capacity. Thus, the study provides new insights into how the H2 S signal regulates tolerance to low-temperature stress and provides the basis for further gene function and detection.

5-Aminolevulinic acid promotes low-light tolerance by regulating chloroplast ultrastructure, photosynthesis, and antioxidant capacity in tall fescue.

The vital signaling molecule 5-Aminolevulinic acid (ALA) plays critical roles in signal transduction and biological modulation under abiotic stresses. In this study, we explored the effects of exogenous ALA on low-light (LL) stress-induced photosynthesis and antioxidant system damage in tall fescue (Festuca arundinacea Schreb.) seedlings. LL stress decreased morphological index values and chlorophyll contents, while also reduced net photosynthetic rate (Pn) and the maximum quantum yield of photosystem II photochemistry (Fv/Fm). Notably, these restrictions were substantially alleviated by exogenous ALA. Moreover, the contents of chlorophyll and its synthetic precursors were significantly increased after ALA treatment. Meanwhile, ALA observably enhanced expression level of FaCHLG, FaHEMA, FaPOR, and FaCAO, which encode the chlorophyll precursors biosynthesis enzymes. Exogenous ALA repaired the damage to the chloroplast ultrastructure caused by LL stress and promoted the formation of ordered thylakoids and grana lamella. ALA also improved Rubisco activity and expression level of the photosynthetic enzyme genes FaRuBP, FaPRK, and FaGADPH. Additionally, application of exogenous ALA decreased relative electrolytic leakage and the accumulation of malondialdehyde (MDA), hydrogen peroxide (H2O2), and superoxide radicals (O2∙-), and increased the gene expression levels and activity of antioxidant enzymes. The ratios of ascorbic acid (AsA) to dehydroascorbic acid (DHA) and reduced glutathione (GSH) to oxidized glutathione (GSSG) were also increased significantly by application of ALA. Furthermore, all responses could be reversed by treatment with levulinic acid (LA). Thus, these results indicated that ALA protects tall fescue from LL stress through scavenging ROS, improving photosynthetic enzyme activity levels, increasing photosynthetic pigments contents, repairing chloroplast damage, and enhancing the photosynthesis rate.

Paclobutrazol Ameliorates Low-Light-Induced Damage by Improving Photosynthesis, Antioxidant Defense System, and Regulating Hormone Levels in Tall Fescue.

Paclobutrazol (PBZ) is a plant-growth regulator (PGR) in the triazole family that enhances plant tolerance to environmental stresses. Low-light (LL) intensity is a critical factor adversely affecting the growth of tall fescue (Festuca arundinacea Schreb.). Therefore, in this study, tall fescue seedlings were treated with PBZ under control and LL conditions to investigate the effects of PBZ on enhancing LL stress resistance by regulating the growth, photosynthesis, oxidative defense, and hormone levels. Our results reveal that LL stress reduced the total biomass, chlorophyll (Chl) content, photosynthetic capacity, and photochemical efficiency of photosystem II (PSII) but increased the membrane lipid peroxidation level and reactive oxygen species (ROS) generation. However, the application of PBZ increased the photosynthetic pigment contents, net photosynthetic rate (Pn), maximum quantum yield of PSII photochemistry (Fv/Fm), ribulose-1,5-bisphosphate carboxylase (RuBisCO) activity, and starch content. In addition, PBZ treatment activated the antioxidant enzyme activities, antioxidants contents, ascorbate acid-glutathione (AsA-GSH) cycle, and related gene expression, lessening the ROS burst (H2O2 and O2∙-). However, the gibberellic acid (GA) anabolism was remarkably decreased by PBZ treatment under LL stress, downregulating the transcript levels of kaurene oxidase (KO), kaurenoic acid oxidase (KAO), and GA 20-oxidases (GA20ox). At the same time, PBZ treatment up-regulated 9-cis-epoxycarotenoid dioxygenase (NCED) gene expression, significantly increasing the endogenous abscisic acid (ABA) concentration under LL stress. Thus, our study revealed that PBZ improves the antioxidation and photosynthetic capacity, meanwhile increasing the ABA concentration and decreasing GA concentration, which ultimately enhances the LL stress tolerance in tall fescue.

Occurrence, Distribution, and Genetic Diversity of Alfalfa (Medicago sativa L.) Viruses in Four Major Alfalfa-Producing Provinces of China.

Alfalfa (Medicago sativa L.) is one of the most widely cultivated forage crops in the world. China is the second largest producer of alfalfa in terms of the planting area worldwide, with Gansu, Henan, Inner Mongolia, and Shaanxi provinces being the production hubs. Alfalfa viruses have been reported on a small-scale survey in some of these areas, but they have not been well characterized. In the present study, seven viruses were detected in 12 fields of 10 cities/counties of the four abovementioned provinces by high-throughput sequencing and assembly of small RNA. Their incidence, distribution, and genetic diversity were analyzed by enzyme-linked immunosorbent assay, polymerase chain reaction (PCR)/reverse transcription-PCR and clone sequencing. The results showed that alfalfa mosaic virus (AMV), pea streak virus (PeSV), lucerne transient streak virus (LTSV), alfalfa dwarf virus (ADV), Medicago sativa alphapartitivirus 1 (MsAPV1), MsAPV2, and alfalfa leaf curl virus (ALCV) were the main viruses infecting alfalfa in four examined provinces. AMV and MsAPV1 had the highest incidences in all 4 provinces. SDT analysis of the 7 viruses isolated in China revealed a highly conserved among AMV, LTSV, ADV, MsAPV1, MsAPV2, and ALCV, but the sequence was a high variation between China isolates to abroad isolates in PeSV, ADV, and ALCV. To our knowledge, this is the first report of ADV in Inner Mongolia and Gansu, ALCV in Inner Mongolia, MsAPV1 and MsAPV2 in all 4 provinces, and PeSV and LTSV in China. These findings provide a basis for future research on the genetic evolution of alfalfa viruses in China and on strategies to prevent diseases in alfalfa caused by these viruses.