Genome-wide analysis of the strigolactone biosynthetic and signaling genes in grapevine and their response to salt and drought stresses

Exogenous strigolactone alleviates post-waterlogging stress in grapevine

With global climate change, the frequent occurrence of intense rainfall and aggravation of waterlogging disasters have severely threatened the plant growth and fruit quality of grapevines, which are commercially important fruit crops worldwide. There is accordingly an imperative to clarify the responses of grapevine to waterlogging and to propose appropriate remedial measures. Strigolactone (SL) is a phytohormone associated with plant abiotic stress tolerance, while, its function in plant responses to waterlogging stress remain undetermined. In this study, systematic analyses of the morphology, physiology, and transcriptome changes in grapevine leaves and roots under post-waterlogging and GR24 (a synthetic analog of SL) treatments were performed. Morphological and physiological changes in grapevines in response to post-waterlogging stress, including leaf wilting and yellowing, leaf senescence, photosynthesis inhibition, and increased anti-oxidative systems, could be alleviated by the application of GR24. Moreover, transcriptome analysis revealed that the primary gene functions induced by post-waterlogging stress changed over time; however, they were consistently associated with carbohydrate metabolism. The GR24-induced leaf genes were closely associated with carbohydrate metabolism, photosynthesis, antioxidant systems, and hormone signal transduction, which were considered vital aspects that were influenced by GR24 in grapevine to induce post-waterlogging tolerance. Concerning the roots, an enhancement of microtubules and cytoskeleton for cell construction in GR24 application was proposed to facilitate root system recovery after waterlogging. With this study, we comprehend the knowledge regarding the responses of grapevines to post-waterlogging and the ameliorative effect of GR24 with the insight to the transcriptome changes during these processes.

The Overexpression of Zea mays Strigolactone Receptor Gene D14 Enhances Drought Resistance in Arabidopsis thaliana L

Strigolactones (SLs) represent a recently identified class of plant hormones that are crucial for plant tillering and mycorrhizal symbiosis. The D14 gene, an essential receptor within the SLs signaling pathway, has been well-examined in crops, like rice (Oryza sativa L.) and Arabidopsis (Arabidopsis thaliana L.), yet the research on its influence in maize (Zea mays L.) remains scarce. This study successfully clones and establishes Arabidopsis D14 gene overexpression lines (OE lines). When compared with the wild type (WT), the OE lines exhibited significantly longer primary roots during germination. By seven weeks of age, these lines showed reductions in plant height and tillering, alongside slight decreases in rosette and leaf sizes, coupled with early aging symptoms. Fluorescence-based quantitative assays indicated notable hormonal fluctuations in OE lines versus the WT, implying that D14 overexpression disrupts plant hormonal homeostasis. The OE lines, exposed to cold, drought, and sodium chloride stressors during germination, displayed an especially pronounced resistance to drought. The drought resistance of OE lines, as evident from dehydration-rehydration assays, outmatched that of the WT lines. Additionally, under drought conditions, the OE lines accumulated less reactive oxygen species (ROS) as revealed by the assessment of the related physiological and biochemical parameters. Upon confronting the pathogens Pseudomonas syringae pv. tomato DC3000 (Pst DC3000), post-infection, fluorescence quantitative investigations showed a significant boost in the salicylic acid (SA)-related gene expression in OE lines compared to their WT counterparts. Overall, our findings designate the SL receptor D14 as a key upregulator of drought tolerance and a regulator in the biotic stress response, thereby advancing our understanding of the maize SL signaling pathway by elucidating the function of the pivotal D14 gene.

Strigolactones can be a potential tool to fight environmental stresses in arid lands

BACKGROUND

Environmental stresses pose a significant threat to plant growth and ecosystem productivity, particularly in arid lands that are more susceptible to climate change. Strigolactones (SLs), carotenoid-derived plant hormones, have emerged as a potential tool for mitigating environmental stresses.

METHODS

This review aimed to gather information on SLs' role in enhancing plant tolerance to ecological stresses and their possible use in improving the resistance mechanisms of arid land plant species to intense aridity in the face of climate change.

RESULTS

Roots exude SLs under different environmental stresses, including macronutrient deficiency, especially phosphorus (P), which facilitates a symbiotic association with arbuscular mycorrhiza fungi (AMF). SLs, in association with AMF, improve root system architecture, nutrient acquisition, water uptake, stomatal conductance, antioxidant mechanisms, morphological traits, and overall stress tolerance in plants. Transcriptomic analysis revealed that SL-mediated acclimatization to abiotic stresses involves multiple hormonal pathways, including abscisic acid (ABA), cytokinins (CK), gibberellic acid (GA), and auxin. However, most of the experiments have been conducted on crops, and little attention has been paid to the dominant vegetation in arid lands that plays a crucial role in reducing soil erosion, desertification, and land degradation. All the environmental gradients (nutrient starvation, drought, salinity, and temperature) that trigger SL biosynthesis/exudation prevail in arid regions. The above-mentioned functions of SLs can potentially be used to improve vegetation restoration and sustainable agriculture.

CONCLUSIONS

Present review concluded that knowledge on SL-mediated tolerance in plants is developed, but still in-depth research is needed on downstream signaling components in plants, SL molecular mechanisms and physiological interactions, efficient methods of synthetic SLs production, and their effective application in field conditions. This review also invites researchers to explore the possible application of SLs in improving the survival rate of indigenous vegetation in arid lands, which can potentially help combat land degradation problems.

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.

Physiological and Transcriptomic Evaluation of Drought Effect on Own-Rooted and Grafted Grapevine Rootstock (1103P and 101-14MGt)

Grapevines worldwide are grafted onto Vitis spp. rootstocks in order to improve their tolerance to biotic and abiotic stresses. Thus, the response of vines to drought is the result of the interaction between the scion variety and the rootstock genotype. In this work, the responses of genotypes to drought were evaluated on 1103P and 101-14MGt plants, own-rooted and grafted with Cabernet Sauvignon, in three different water deficit conditions (80, 50, and 20% soil water content, SWC). Gas exchange parameters, stem water potential, root and leaf ABA content, and root and leaf transcriptomic response were investigated. Under well-watered conditions, gas exchange and stem water potential were mainly affected by the grafting condition, whereas under sever water deficit they were affected by the rootstock genotype. Under severe stress conditions (20% SWC), 1103P showed an "avoidance" behavior. It reduced stomatal conductance, inhibited photosynthesis, increased ABA content in the roots, and closed the stomata. The 101-14MGt maintained a high photosynthetic rate, limiting the reduction of soil water potential. This behavior results in a "tolerance" strategy. An analysis of the transcriptome showed that most of the differentially expressed genes were detected at 20% SWC, and more significantly in roots than in leaves. A core set of genes has been highlighted on the roots as being related to the root response to drought that are not affected by genotype nor grafting. Genes specifically regulated by grafting and genes specifically regulated by genotype under drought conditions have been identified as well. The 1103P, more than the 101-14MGt, regulated a high number of genes in both own-rooted and grafted conditions. This different regulation revealed that 1103P rootstock readily perceived the water scarcity and rapidly faced the stress, in agreement with its avoidance strategy.

CpMAX1a, a Cytochrome P450 Monooxygenase Gene of Chimonanthus praecox Regulates Shoot Branching in Arabidopsis

Strigolactones (SLs) are a class of important hormones in the regulation of plant branching. In the model plant Arabidopsis, AtMAX1 encodes a cytochrome P450 protein and is a crucial gene in the strigolactone synthesis pathway. Yet, the regulatory mechanism of MAX1 in the shoot branching of wintersweet (Chimonanthus praecox) remains unclear. Here we identified and isolated three MAX1 homologous genes, namely CpMAX1a, CpMAX1b, and CpMAX1c. Quantitative real-time PCR (qRT-PCR) revealed the expression of CpMAX1a in all tissues, being highest in leaves, whereas CpMAX1b was only expressed in stems, while CpMAX1c was expressed in both roots and stem tips. However, CpMAX1a’s expression decreased significantly after decapitation; hence, we verified its gene function. CpMAX1a was located in Arabidopsis chloroplasts. Overexpressing CpMAX1a restored the phenotype of the branching mutant max1−3, and reduced the rosette branch number, but resulted in no significant phenotypic differences from the wild type. Additionally, expression of AtBRC1 was significantly upregulated in transgenic lines, indicating that the CpMAX1a gene has a function similar to the homologous gene of Arabidopsis. In conclusion, our study shows that CpMAX1a plays a conserved role in regulating the branch development of wintersweet. This work provides a molecular and theoretical basis for better understanding the branch development of wintersweet.