Differential gene expression in response to water deficit in leaf and root tissues of soybean genotypes with contrasting tolerance profiles

CRISPR-Cas9-mediated editing of GmARM improves resistance to multiple stresses in soybean

The growth and development of soybean plants can be affected by both abiotic and biotic stressors, such as saline-alkali stress and Phytophthora root rot. In this study, we identified a stress-related gene-GmARM-whose promoter contained several hormone-response and stress-regulatory elements, including ABRE, TCA element, STRE, and MBS. qRT-PCR analysis showed that the expression of GmARM was the highest in seeds at 55 days after flowering. Furthermore, this gene was upregulated after exposure to saline-alkali stress and Phytophthora root rot infection at the seedling stage. Thus, we generated GmARM mutants using the CRISPR-Cas9 system to understand the role of this gene in stress response. T3 plants showed significantly improved salt tolerance, alkali resistance, and disease resistance, with a significantly higher survival rate than the wildtype plants. Moreover, mutations in GmARM affected the expression of related stress-resistance genes, indicating that GmARM mutants achieved multiple stress tolerance. Therefore, this study provides a foundation for further exploration of the genes involved in resistance to multiple stresses in soybean that can be used for breeding multiple stress-resistance soybean varieties.

Complete genome sequence of Bacillus velezensis strain Ag109, a biocontrol agent against plant-parasitic nematodes and Sclerotinia sclerotiorum

Soybean is the main oilseed cultivated worldwide. Even though Brazil is the world's largest producer and exporter of soybean, its production is severely limited by biotic factors. Soil borne diseases are the most damaging biotic stressors since they significantly reduce yield and are challenging to manage. In this context, the present study aimed to evaluate the potential of a bacterial strain (Ag109) as a biocontrol agent for different soil pathogens (nematodes and fungi) of soybean. In addition, the genome of Ag109 was wholly sequenced and genes related to secondary metabolite production and plant growth promotion were mined. Ag109 showed nematode control in soybean and controlled 69 and 45% of the populations of Meloidogyne javanica and Pratylenchus brachyurus, respectively. Regarding antifungal activity, these strains showed activity against Macrophomia phaseolina, Rhizoctonia solani, and Sclerotinia sclerotiorum. For S. sclerotiorum, this strain increased the number of healthy plants and root dry mass compared to the control (with inoculation). Based on the average nucleotide identity and digital DNA-DNA hybridization, this strain was identified as Bacillus velezensis. Diverse clusters of specific genes related to secondary metabolite biosynthesis and root growth promotion were identified, highlighting the potential of this strain to be used as a multifunctional microbial inoculant that acts as a biological control agent while promoting plant growth in soybean.

PEG-induced physiological drought for screening winter wheat genotypes sensitivity - integrated biochemical and chlorophyll a fluorescence analysis

This study aimed to screen different winter wheat genotypes at the onset of metabolic changes induced by water deficit to comprehend possible adaptive features of photosynthetic apparatus function and structure to physiological drought. The drought treatment was the most influential variable affecting plant growth and relative water content, and genotype variability determined with what intensity varieties of winter wheat seedlings responded to water deficit. PEG-induced drought, as expected, changed phenomenological energy fluxes and the efficiency with which an electron is transferred to final PSI acceptors. Based on the effect size, fluorescence parameters were grouped to represent photochemical parameters, that is, the donor and acceptor side of PSII (PC1); the thermal phase of the photosynthetic process, or the electron flow around PSI, and the chain of electrons between PSII and PSI (PC2); and phenomenological energy fluxes per cross-section (PC3). Furthermore, four distinct clusters of genotypes were discerned based on their response to imposed physiological drought, and integrated analysis enabled an explanation of their reactions' specificity. The most reliable JIP-test parameters for detecting and comparing the drought impact among tested genotypes were the variable fluorescence at K, L, I step, and PI_TOT. To conclude, developing and improving screening methods for identifying and evaluating functional relationships of relevant characteristics that are useful for acclimation, acclimatization, and adaptation to different types of drought stress can contribute to the progress in breeding research of winter wheat drought-tolerant lines.

Metabolic, physiological and anatomical responses of soybean plants under water deficit and high temperature condition

Water deficit (WD) combined with high temperature (HT) is the major factor limiting agriculture worldwide, and it is predicted to become worse according to the current climate change scenario. It is thus important to understand how current cultivated crops respond to these stress conditions. Here we investigated how four soybean cultivars respond to WD and HT isolated or in combination at metabolic, physiological, and anatomical levels. The WD + HT increased the level of stress in soybean plants when compared to plants under well-watered (WW), WD, or HT conditions. WD + HT exacerbates the increases in ascorbate peroxidase activity, which was associated with the greater photosynthetic rate in two cultivars under WD + HT. The metabolic responses to WD + HT diverge substantially from plants under WW, WD, or HT conditions. Myo-inositol and maltose were identified as WD + HT biomarkers and were connected to subnetworks composed of catalase, amino acids, and both root and leaf osmotic potentials. Correlation-based network analyses highlight that the network heterogeneity increased and a higher integration among metabolic, physiological, and morphological nodes is observed under stress conditions. Beyond unveiling biochemical and metabolic WD + HT biomarkers, our results collectively highlight that the mechanisms behind the acclimation to WD + HT cannot be understood by investigating WD or HT stress separately.

Metabolic adjustment and regulation of gene expression are essential for increased resistance to severe water deficit and resilience post-stress in soybean

Background

Soybean is the main oilseed crop grown in the world; however, drought stress affects its growth and physiology, reducing its yield. The objective of this study was to characterize the physiological, metabolic, and genetic aspects that determine differential resistance to water deficit in soybean genotypes.

Methods

Three soybean genotypes were used in this study, two lineages (L11644 and L13241), and one cultivar (EMBRAPA 48-C48). Plants were grown in pots containing 8 kg of a mixture of soil and sand (2:1) in a greenhouse under sunlight. Soil moisture in the pots was maintained at field capacity until the plants reached the stage of development V4 (third fully expanded leaf). At this time, plants were subjected to three water treatments: Well-Watered (WW) (plants kept under daily irrigation); Water Deficit (WD) (withholding irrigation until plants reached the leaf water potential at predawn of -1.5 ± 0.2 MPa); Rewatered (RW) (plants rehydrated for three days after reached the water deficit). The WW and WD water treatments were evaluated on the eighth day for genotypes L11644 and C48, and on the tenth day for L13241, after interruption of irrigation. For the three genotypes, the treatment RW was evaluated after three days of resumption of irrigation. Physiological, metabolic and gene expression analyses were performed.

Results

Water deficit inhibited growth and gas exchange in all genotypes. The accumulation of osmolytes and the concentrations of chlorophylls and abscisic acid (ABA) were higher in L13241 under stress. The metabolic adjustment of lineages in response to WD occurred in order to accumulate amino acids, carbohydrates, and polyamines in leaves. The expression of genes involved in drought resistance responses was more strongly induced in L13241. In general, rehydration provided recovery of plants to similar conditions of control treatment. Although the C48 and L11644 genotypes have shown some tolerance and resilience responses to severe water deficit, greater efficiency was observed in the L13241 genotype through adjustments in morphological, physiological, genetic and metabolic characteristics that are combined in the same plant. This study contributes to the advancement in the knowledge about the resistance to drought in cultivated plants and provides bases for the genetic improvement of the soybean culture.

Uncovering the roles of hemoglobins in soybean facing water stress

Water stress drastically hinders crop yield, including soybean - one of the world's most relevant feeding crops - threatening the food security of an ever-growing global population. Hemoglobins (GLBs) are involved in water stress tolerance; however, the role they effectively play in soybean remains underexplored. In this study, in silico and in vivo analyses were performed to identify soybean GLBs, capture their transcriptional profile under water stress, and overexpress promising members to assess how soybean cope with waterlogging. Seven GLBs were found, two GLB1 (non-symbiotic) and five GLB2 (symbiotic or leghemoglobins). Three out of the seven GLBs were differentially expressed in soybean RNA-seq libraries of water stress and were evaluated by real-time PCR. Consistently, GmGLB1-1 and GmGLB1-2 were moderately and highly expressed under waterlogging, respectively. Composite plants with roots overexpressing GmGLB1-1 or GmGLB1-2 (mostly) showed higher transcript abundance of stress-defensive genes involved in anaerobic, nitrogen, carbon, and antioxidant metabolism when subjected to waterlogging. In addition, soybean bearing p35S:GmGLB1-2 had lower H2O2 root content, a reactive oxygen species (ROS), under water excess compared with the control condition. Altogether these results suggest that GmGLB1-2 is a strong candidate for soybean genetic engineering to generate waterlogging-tolerant soybean cultivars.