Exogenous strigolactones enhance tolerance in soybean seedlings in response to alkaline stress

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.

Identification and expression of strigolactone biosynthesis and signaling genes and the in vitro effects of strigolactones in olive (Olea europaea L.)

Strigolactones (SLs), synthesized in plant roots, play a dual role in modulating plant growth and development, and in inducing the germination of parasitic plant seeds and arbuscular mycorrhizal fungi in the rhizosphere. As phytohormones, SLs are crucial in regulating branching and shaping plant architecture. Despite the significant impact of branching strategies on the yield performance of fruit crops, limited research has been conducted on SLs in these crops. In our study, we identified the transcript sequences of SL biosynthesis and signaling genes in olive (Olea europaea L.) using rapid amplification of cDNA ends. We predicted the corresponding protein sequences, analyzed their characteristics, and conducted molecular docking with bioinformatics tools. Furthermore, we quantified the expression levels of these genes in various tissues using quantitative real-time PCR. Our findings demonstrate the predominant expression of SL biosynthesis and signaling genes (OeD27, OeMAX3, OeMAX4, OeMAX1, OeD14, and OeMAX2) in roots and lateral buds, highlighting their importance in branching. Treatment with rac-GR24, an SL analog, enhanced the germination frequency of olive seeds in vitro compared with untreated embryos. Conversely, inhibition of SL biosynthesis with TIS108 increased lateral bud formation in a hard-to-root cultivar, underscoring the role of SLs as phytohormones in olives. These results suggest that modifying SL biosynthesis and signaling pathways could offer novel approaches for olive breeding, with potential applicability to other fruit crops.

Physiological and RNA-Seq Analyses on Exogenous Strigolactones Alleviating Drought by Improving Antioxidation and Photosynthesis in Wheat (Triticum aestivum L.)

Drought poses a significant challenge to global wheat production, and the application of exogenous phytohormones offers a convenient approach to enhancing drought tolerance of wheat. However, little is known about the molecular mechanism by which strigolactones (SLs), newly discovered phytohormones, alleviate drought stress in wheat. Therefore, this study is aimed at elucidating the physiological and molecular mechanisms operating in wheat and gaining insights into the specific role of SLs in ameliorating responses to the stress. The results showed that SLs application upregulated the expression of genes associated with the antioxidant defense system (Fe/Mn-SOD, PER1, PER22, SPC4, CAT2, APX1, APX7, GSTU6, GST4, GOR, GRXC1, and GRXC15), chlorophyll biogenesis (CHLH, and CPX), light-harvesting chlorophyll A-B binding proteins (WHAB1.6, and LHC Ib-21), electron transfer (PNSL2), E3 ubiquitin-protein ligase (BB, CHIP, and RHY1A), heat stress transcription factor (HSFA1, HSFA4D, and HSFC2B), heat shock proteins (HSP23.2, HSP16.9A, HSP17.9A, HSP21, HSP70, HSP70-16, HSP70-17, HSP70-8, HSP90-5, and HSP90-6), DnaJ family members (ATJ1, ATJ3, and DJA6), as well as other chaperones (BAG1, CIP73, CIPB1, and CPN60I). but the expression level of genes involved in chlorophyll degradation (SGR, NOL, PPH, PAO, TIC55, and PTC52) as well as photorespiration (AGT2) was found to be downregulated by SLs priming. As a result, the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were enhanced, and chlorophyll content and photosynthetic rate were increased, which indicated the alleviation of drought stress in wheat. These findings demonstrated that SLs alleviate drought stress by promoting photosynthesis through enhancing chlorophyll levels, and by facilitating ROS scavenging through modulation of the antioxidant system. The study advances understandings of the molecular mechanism underlying SLs-mediated drought alleviation and provides valuable insights for implementing sustainable farming practice under water restriction.

Strigolactone signaling gene from soybean GmMAX2a enhances the drought and salt-alkaline resistance in Arabidopsis via regulating transcriptional profiles of stress-related genes

Strigolactone (SL) is a new plant hormone, which not only plays an important role in stimulating seed germination, plant branching, and regulating root development, but also plays an important role in the response of plants to abiotic stresses. In this study, the full-length cDNA of a soybean SL signal transduction gene (GmMAX2a) was isolated, cloned and revealed an important role in abiotic stress responses. Tissue-specific expression analysis by qRT-PCR indicated that GmMAX2a was expressed in all tissues of soybean, but highest expression was detected in seedling stems. Moreover, upregulation of GmMAX2a transcript expression under salt, alkali, and drought conditions were noted at different time points in soybean leaves compared to roots. Additionally, histochemical GUS staining studies revealed the deep staining in P_GmMAX2a: GUS transgenic lines compared to WT indicating active involvement of GmMAX2a promoter region to stress responses. To further investigate the function of GmMAX2a gene in transgenic Arabidopsis, Petri-plate experiments were performed and GmMAX2a OX lines appeared with longer roots and improved fresh biomass compared to WT plants to NaCl, NaHCO₃, and mannitol supplementation. Furthermore, the expression of several stress-related genes such as RD29B, SOS1, NXH1, AtRD22, KIN1, COR15A, RD29A, COR47, H+-APase, NADP-ME, NCED3, and P5CS were significantly high in GmMAX2a OX plants after stress treatment compared to WT plants. In conclusion, GmMAX2a improves soybean tolerance towards abiotic stresses (salt, alkali, and drought). Hence, GmMAX2a can be considered a candidate gene for transgenic breeding against various abiotic stresses in plants.

SLs signal transduction gene CsMAX2 of cucumber positively regulated to salt, drought and ABA stress in Arabidopsis thaliana L

Recent studies have demonstrated that strigolactones (SLs) participate in the regulation of stress adaptation, however, the mechanisms remain elusive. MAX2 (MORE AXILLARY GROWTH2) is the key gene in the signal transduction pathway of SLs. This study aimed to clone and functionally characterize the CsMAX2 gene of cucumber in Arabidopsis. The results showed that the expression levels of the CsMAX2 gene changed significantly after salt, drought, and ABA stresses in cucumber. Moreover, the overexpression of CsMAX2 promoted stress tolerance and increased the germination rate and root length of Arabidopsis thaliana. Meanwhile, the content of chlorophyll increased and malondialdehyde decreased in CsMAX2 OE lines under salt and drought stresses. Additionally, the expression levels of stress-related marker genes, especially AREB1 and COR15A, were significantly upregulated under salt stress, while the expression levels of all genes were upregulated under drought stress, except ABI4 and ABI5 genes. The level of NCED3 continued to rise under both salt and drought stresses. In addition, D10 and D27 gene expression level also showed a continuous increase under ABA stress. The result suggested the interaction between SL and ABA in the process of adapting to stress. Overall, CsMAX2 could positively regulate salt, drought, and ABA stress resistance, and this process correlated with ABA transduction.

Unfolding molecular switches for salt stress resilience in soybean: recent advances and prospects for salt-tolerant smart plant production

The increasing sodium salts (NaCl, NaHCO3, NaSO4 etc.) in agricultural soil is a serious global concern for sustainable agricultural production and food security. Soybean is an important food crop, and their cultivation is severely challenged by high salt concentration in soils. Classical transgenic and innovative breeding technologies are immediately needed to engineer salt tolerant soybean plants. Additionally, unfolding the molecular switches and the key components of the soybean salt tolerance network are crucial for soybean salt tolerance improvement. Here we review our understandings of the core salt stress response mechanism in soybean. Recent findings described that salt stress sensing, signalling, ionic homeostasis (Na⁺/K⁺) and osmotic stress adjustment might be important in regulating the soybean salinity stress response. We also evaluated the importance of antiporters and transporters such as Arabidopsis K⁺ Transporter 1 (AKT1) potassium channel and the impact of epigenetic modification on soybean salt tolerance. We also review key phytohormones, and osmo-protectants and their role in salt tolerance in soybean. In addition, we discuss the progress of omics technologies for identifying salt stress responsive molecular switches and their targeted engineering for salt tolerance in soybean. This review summarizes recent progress in soybean salt stress functional genomics and way forward for molecular breeding for developing salt-tolerant soybean plant.