Water-Deficit Tolerance in Sweet Potato [Ipomoea batatas (L.) Lam.] by Foliar Application of Paclobutrazol: Role of Soluble Sugar and Free Proline

Insight of PBZ mediated drought amelioration in crop plants

Water scarcity is a significant environmental limitation to plant productivity as drought-induced crop output losses are likely to outnumber losses from all other factors. In this context, triazole compounds have recently been discovered to act as plant growth regulators and multi-stress protectants such as heat, chilling, drought, waterlogging, heavy metals, etc. Paclobutrazol (PBZ) [(2RS, 3RS)-1-(4-chlorophenyl)- 4, 4-dimethyl-2-(1H-1, 2, 4-trizol-1-yl)-pentan-3-ol)] disrupts the isoprenoid pathway by blocking ent-kaurene synthesis, affecting gibberellic acid (GA) and abscisic acid (ABA) hormone levels. PBZ affects the level of ethylene and cytokinin by interfering with their biosynthesis pathways. Through a variety of physiological responses, PBZ improves plant survival under drought. Some of the documented responses include a decrease in transpiration rate (due to reduced leaf area), higher diffusive resistance, relieving reduction in water potential, greater relative water content, less water use, and increased antioxidant activity. We examined and discussed current findings as well as the prospective application of PBZ in regulating crop growth and ameliorating abiotic stresses in this review. Furthermore, the influence of PBZ on numerous biochemical, physiological, and molecular processes is thoroughly investigated, resulting in increased crop yield.

Efforts towards overcoming drought stress in crops: Revisiting the mechanisms employed by plant growth-promoting bacteria

Globally, agriculture is under a lot of pressure due to rising population and corresponding increases in food demand. However, several variables, including improper mechanization, limited arable land, and the presence of several biotic and abiotic pressures, continually impact agricultural productivity. Drought is a notable destructive abiotic stress and may be the most serious challenge confronting sustainable agriculture, resulting in a significant crop output deficiency. Numerous morphological and physiological changes occur in plants as a result of drought stress. Hence, there is a need to create mitigation techniques since these changes might permanently harm the plant. Current methods used to reduce the effects of drought stress include the use of film farming, super-absorbent hydrogels, nanoparticles, biochar, and drought-resistant plant cultivars. However, most of these activities are money and labor-intensive, which offer limited plant improvement. The use of plant-growth-promoting bacteria (PGPB) has proven to be a preferred method that offers several indirect and direct advantages in drought mitigation. PGPB are critical biological elements which have favorable impacts on plants’ biochemical and physiological features, leading to improved sugar production, relative water content, leaf number, ascorbic acid levels, and photosynthetic pigment quantities. This present review revisited the impacts of PGPB in ameliorating the detrimental effects of drought stress on plants, explored the mechanism of action employed, as well as the major challenges encountered in their application for plant growth and development.

Expression of Potato StDRO1 in Arabidopsis Alters Root Architecture and Drought Tolerance

Potato (Solanum tuberosum L) is the third important crop for providing calories to a large human population, and is considered sensitive to moderately sensitive to drought stress conditions. The development of drought-tolerant, elite varieties of potato is a challenging task, which can be achieved through molecular breeding. Recently, the DEEPER ROOTING 1 (DRO1) gene has been identified in rice, which influences plant root system and regulates grain yield under drought stress conditions. The potato StDRO1 protein is mainly localized in the plasma membrane of tobacco leaf cells, and overexpression analysis of StDRO1 in Arabidopsis resulted in an increased lateral root number, but decreased lateral root angle, lateral branch angle, and silique angle. Additionally, the drought treatment analysis indicated that StDRO1 regulated drought tolerance and rescued the defective root architecture and drought-tolerant phenotypes of Atdro1, an Arabidopsis AtDRO1 null mutant. Furthermore, StDRO1 expression was significantly higher in the drought-tolerant potato cultivar "Unica" compared to the drought-sensitive cultivar "Atlantic." The transcriptional response of StDRO1 under drought stress occurred significantly earlier in Unica than in Atlantic. Collectively, the outcome of the present investigation elucidated the role of DRO1 function in the alternation of root architecture, which potentially acts as a key gene in the development of a drought stress-tolerant cultivar. Furthermore, these findings will provide the theoretical basis for molecular breeding of drought-tolerant potato cultivars for the farming community.

Interrelation of Ecophysiological and Morpho-Agronomic Parameters in Low Altitude Evaluation of Selected Ecotypes of Sweet Potato (Ipomoea batatas [L.] Lam.)

Sweet potato is a crop with a wide capacity to adapt to adverse conditions. To study the tolerance of the sweet potato to a low-altitude environment, 34 genotypes comprising three groups from different altitude conditions ranging from 18–599, 924–1298, 1401–2555 meters above sea level were evaluated. These genotypes were evaluated through ecophysiological parameters: net photosintetic rate (Pn), stomatal conductance (GS), transpiration (E), leaf internal CO2 (ICO2), vapor pressure deficit (VPD) and leaf internal temperate (LT). sSubsequently, water use efficiency (WUE) and carboxylation efficiency index (CEI) were estimated. Simultaneously, morpho-agronomic characterization of the genotypes was conducted including descriptors and morpho-colorimetric parameters. A wide ecophysiological variability was found among genotypes from high, intermediate and low altitudes, when those were evaluated under low altitude conditions. The genotypes that presented major soil coverage efficiency and leaf size showed greater Pn, WUE and CEI, and Low VPD and E, aspects that benefited the ability to form roots the under low-altitude environment. The altitudinal origin of the genotypes influenced the ecophysiological response under low altitude conditions. The capacity of certain sweet potato genotypes to tolerate low altitude conditions were due to to different mechanisms, such as certain morphoagronomic traits that allowed them to adjust their physiological processes, especially those related to photosynthesis.

Integrated mRNA and microRNA transcriptome analyses provide insights into paclobutrazol inhibition of lateral branching in herbaceous peony

Herbaceous peony (Paeonia lactiflora Pall.) is a new high-end cut flower, but a large number of lateral branches often appear in some excellent cultivars, which is inconvenient for cut flower production. In the present study, we analyzed the effects of paclobutrazol (PBZ) on the lateral branches of P. lactiflora and adopted a next-generation sequencing approach to identify miRNAs and mRNAs that were differentially expressed involved in the PBZ response. Our results indicate that PBZ may inhibit the production of lateral branches on P. lactiflora. There were 827 differentially expressed genes (DEGs) and 104 differentially expressed miRNAs (DEMs). Integrative analysis revealed 29 miRNA-mRNA interactions related to PBZ stress. Our results provided a wealth of genetic information and data on metabolic pathways for revealing the regulatory mechanism of PBZ inhibition of the development of lateral branches in P. lactiflora and provided a new possibility for reducing lateral branch formation in the production of herbaceous peony cut flowers.

NHX1 and eIF4A1-stacked transgenic sweetpotato shows enhanced tolerance to drought stress

Co-expression of Na⁺/H⁺ antiporter NHX1 and DEAD-box RNA helicase eIF4A1 from Arabidopsis positively regulates drought stress tolerance by improving ROS scavenging capacity and maintaining membrane integrity in sweetpotato. Plants evolve multiple strategies for stress adaptation in nature. To improve sweetpotato resistance to drought stress, transgenic sweetpotato plants overexpressing the Arabidopsis Na⁺/H⁺ antiporter, NHX1, and the translation initiation factor elF4A1 were characterized for phenotypic traits and physiological performance. Without drought treatment, the NHX1-elF4A1 stacked lines (NE lines) showed normal, vigorous growth comparable to the WT plants. The NE plants showed dense green foliage with delayed leaf senescence and developed more roots than WT plants under drought treatment for 18 days. Compared to WT plants, higher level of reactive oxygen scavenging capacity was detected in NE lines as indicated by reduced H₂O₂ accumulation as well as increased superoxide dismutase activity and proline content. The relative ion leakage and malondialdehyde content were reduced in NE plants, indicating improved maintenance of intact membranes system. Both NE plants and NHX1-overexpressing plants (N lines) showed larger aerial parts and well-developed root system compared to WT plants under the drought stress conditions, likely due to the improved antioxidant capacity. The NE plants showed better ROS scavenging than N-line plants. All N- and NE-line plants produced normal storage roots with similar yields as WT in the field under normal growth conditions. These results demonstrated the potential to enhance sweetpotato productivity through stacking genes that are involved in ion compartmentalization and translation initiation.

Dynamic responses of Haloxylon ammodendron to various degrees of simulated drought stress

Haloxylon ammodendron, a C4 perennial, succulent and xero-halophytic shrub, is highly resistant to harsh environments, therefore, exploring the stress resistance mechanism will be beneficial for the use of xerophytes to prevent desertification. To determine osmotic adjustment (OA) and antioxidase functions under simulated drought stress, 8-week-old seedlings were treated with sorbitol solutions to maintain osmotic potentials (Ψs) at a control and -0.5 and -1.0 MPa. Under -0.5 MPa osmotic stress, H. ammodendron stably maintained the water content of assimilating branches, a result that was not significantly different from the result of the control group. Moreover, the Ψs decreased significantly, which helped plants absorb water efficiently from the environment, as H. ammodendron accumulated massive osmotic regulators in its assimilating branches to adjust shoot Ψs. Specifically, the contribution of Na⁺ to shoot Ψs was up to 45%, and Na⁺ became the main osmotic regulator of OA. During the treatments, the content and contribution of K⁺ remained stable. However, the total contribution of three organic osmotic regulators (free proline, betaine and soluble sugar) was only 20%, and betaine was the main organic osmotic regulator, accounting for approximately 15% of the 20% contribution. Moreover, H. ammodendron seedlings presented strong antioxidases, especially when there was a high activity level of superoxide dismutase, and with an increase in treatment time and degree of osmotic stress, the activity of peroxidase and catalase increased significantly. Substantial accumulation of osmotic adjustment substances was an important strategy for H. ammodendron to cope with simulated drought stress, in particular, H. ammodendron absorbed much Na⁺ and transported Na⁺ into the assimilating branch for OA. The scavenging of reactive oxygen species by antioxidases was another adaptation strategy for H. ammodendron to adapt to simulated drought stress.

Knock-down the expression of TaH2B-7D using virus-induced gene silencing reduces wheat drought tolerance

Background

Drought is a major abiotic stress affecting global wheat (Triticum aestivum L.) production. Exploration of drought-tolerant genes is essential for the genetic improvement of drought tolerance in wheat. Previous studies have shown that some histone encoding genes are involved in plant drought tolerance. However, whether the H2B family genes are involved in drought stress response remains unclear.

Methods

Here, we identified a wheat histone H2B family gene, TaH2B-7D, which was significantly up-regulated under drought stress conditions. Virus-induced gene silencing (VIGS) technology was used to further verify the function of TaH2B-7D in wheat drought tolerance. The phenotypic and physiological changes were examined in the TaH2B-7D knock-down plants.

Results

In the TaH2B-7D knock-down plants, relative electrolyte leakage rate and malonaldehyde (MDA) content significantly increased, while relative water content (RWC) and proline content significantly decreased compared with those in the non-knocked-down plants under drought stress conditions. TaH2B-7D knock-down plants exhibited severe sagging, wilting and dwarf phenotypes under drought stress conditions, but not in the non-knocked-down plants, suggesting that the former were more sensitive to drought stress.

Conclusion

These results indicate that TaH2B-7D potentially plays a vital role in conferring drought tolerance in wheat.

Xerophyta viscosa Aldose Reductase, XvAld1, Enhances Drought Tolerance in Transgenic Sweetpotato

Sweetpotato is a significant crop which is widely cultivated particularly in the developing countries with high and stable yield. However, drought stress is a major limiting factor that antagonistically influences the crop's productivity. Dehydration stress caused by drought causes aggregation of reactive oxygen species (ROS) in plants, and aldose reductases are first-line safeguards against ROS caused by oxidative stress. In the present study, we generated transgenic sweetpotato plants expressing aldose reductase, XvAld1 isolated from Xerophyta viscosa under the control of a stress-inducible promoter via Agrobacterium-mediated transformation. Our results demonstrated that the transgenic sweetpotato lines displayed significant enhanced tolerance to simulated drought stress and enhanced recuperation after rehydration contrasted with wild-type plants. In addition, the transgenic plants exhibited improved photosynthetic efficiency, higher water content and more proline accumulation under dehydration stress conditions compared with wild-type plants. These results demonstrate that exploiting the XvAld1 gene is not only a compelling and attainable way to improve sweetpotato tolerance to drought stresses without causing any phenotypic imperfections but also a promising gene candidate for more extensive crop improvement.

Xerophyta viscosa Aldose Reductase, XvAld1, Enhances Drought Tolerance in Transgenic Sweetpotato

Sweetpotato is a significant crop which is widely cultivated particularly in the developing countries with high and stable yield. However, drought stress is a major limiting factor that antagonistically influences the crop's productivity. Dehydration stress caused by drought causes aggregation of reactive oxygen species (ROS) in plants, and aldose reductases are first-line safeguards against ROS caused by oxidative stress. In the present study, we generated transgenic sweetpotato plants expressing aldose reductase, XvAld1 isolated from Xerophyta viscosa under the control of a stress-inducible promoter via Agrobacterium-mediated transformation. Our results demonstrated that the transgenic sweetpotato lines displayed significant enhanced tolerance to simulated drought stress and enhanced recuperation after rehydration contrasted with wild-type plants. In addition, the transgenic plants exhibited improved photosynthetic efficiency, higher water content and more proline accumulation under dehydration stress conditions compared with wild-type plants. These results demonstrate that exploiting the XvAld1 gene is not only a compelling and attainable way to improve sweetpotato tolerance to drought stresses without causing any phenotypic imperfections but also a promising gene candidate for more extensive crop improvement.