Physiological performance and differential expression profiling of genes associated with drought tolerance in root tissue of four contrasting varieties of two Gossypium species

PEG treatment is unsuitable to study root related traits as it alters root anatomy in barley (Hordeum vulgare L.)

BACKGROUND

The frequency and severity of abiotic stress events, especially drought, are increasing due to climate change. The plant root is the most important organ for water uptake and the first to be affected by water limitation. It is therefore becoming increasingly important to include root traits in studies on drought stress tolerance. However, phenotyping under field conditions remains a challenging task. In this study, plants were grown in a hydroponic system with polyethylene glycol as an osmotic stressor and in sand pots to examine the root system of eleven spring barley genotypes. The root anatomy of two genotypes with different response to drought was investigated microscopically.

RESULTS

Root diameter increased significantly (p < 0.05) under polyethylene glycol treatment by 54% but decreased significantly (p < 0.05) by 12% under drought stress in sand pots. Polyethylene glycol treatment increased root tip diameter (51%) and reduced diameter of the elongation zone (14%) compared to the control. Under drought stress, shoot mass of plants grown in sand pots showed a higher correlation (r = 0.30) with the shoot mass under field condition than polyethylene glycol treated plants (r = -0.22).

CONCLUSION

These results indicate that barley roots take up polyethylene glycol by the root tip and polyethylene glycol prevents further water uptake. Polyethylene glycol-triggered osmotic stress is therefore unsuitable for investigating root morphology traits in barley. Root architecture of roots grown in sand pots is more comparable to roots grown under field conditions.

Low-temperature perception and modulations in Ocimum basilicum commercial cultivar CIM-Shishir: Biosynthetic potential with insight towards climate-smart resilience

The newly released interspecific hybrid variety CIM-Shishir, resulting from a cross between Ocimum basilicum and Ocimum kilimandscharicum claims to be a multicut, lodging resistant, cold tolerant, high essential oil yielding with linalool rich variety. It has a purple-green stem and has a unique feature and advantage of better survival in the winter season than other O. basilicum varieties, illustrating its physiological mechanisms for cold tolerance. In this study, we subjected both the CIM-Shishir variety and a control plant to cold stress to investigate the impact of low temperatures on various physiological, trichome developments, secondary metabolite constitution aspects related to essential oil production, and gene expression. The analysis revealed a significantly higher density and altered morphology of trichomes on the leaf surface of the variety subjected to low temperatures, indicating its adaptation to cold conditions. Furthermore, when comparing the treated plants under low-temperature stress, it was observed that the relative electrolyte leakage and Malondialdehyde (MDA) contents substantially increased in the control in contrast to the CIM-Shishir variety. This finding suggests that CIM-Shishir exhibits superior cold tolerance. Additionally, an increase in proline content was noted in the variety exposed to low temperatures compared to the control. Moreover, the chlorophyll and anthocyanin content gradually increased with prolonged exposure to low-temperature stress in the newly developed variety, indicating its ability to maintain photosynthetic capacity and adapt to cold conditions. The activities of superoxide dismutase (SOD) also increased under low-temperature conditions in the CIM-Shishir variety, further highlighting its cold tolerance behaviour. In our research, we investigated the comprehensive molecular mechanisms of cold response in Ocimum. We analyzed the expression of key genes associated with cold tolerance in two plant groups: the newly developed hybrid variety known as CIM-Shishir Ocimum, which exhibits cold tolerance, and the control plants susceptible to cold climates that include WRKY53, ICE1, HOS1, COR47, LOS15, DREB5, CBF4, LTI6, KIN, and ERD2. These genes exhibited significantly higher expression levels in the CIM-Shishir variety compared to the control, shedding light on the genetic basis of its cold tolerance. The need for climate-smart, resilient high-yielding genotype is of high importance due to varied climatic conditions as this will hit the yield drastically and further to the economic sectors including farmers and many industries that are dependent on the bioactive constituents of Ocimum.

Spectral reflectance and fluorescence is a rapid, non-destructive tool for drought tolerance monitoring in Withania somnifera (L.) Dunal

Withania somnifera plants were exposed to drought stress for 23 days. Relative water content (RWC), gaseous exchange, fluorescence parameters, and spectral reflectance changes were monitored under drought stress. Assimilation rate and RWC decreased by 81% and 65%, respectively, during drought exposure of 23 days. Photosynthetic reflectance index (PRI) and water index (WI) showed a decreasing pattern under drought stress and correlated with Amax and RWC. Anthocyanin reflectance index and anthocyanin content increased with drought stress. Similarly, rational among R727, R696, R770, and R731 reflects chlorophyll content and Chl a/b ratio and copes with actual chlorophyll content. Fluorescence changes showed the opening and closing of PSII reaction centers, while absorbance change at 830/875 nm showed activity and energy balance of PSI. Non-photochemical quenching increased under drought, which showed depoxydation of xanthine cycle pigment. Energy balance at the acceptor and donor side of PSI adjusted under drought stress by increasing electron carrying limitation at donor side. Energy balance between PSI and PSII is maintained by increasing cyclic electron flux under mild drought stress. Both protective mechanism depoxydation of xanthine cycle pigment and enhancement of cyclic electron flux reduced or diminished under severe drought stress. Decrease in leaf area and stomatal closure may cause a reduction in transpiration that results into loss of RWC and altered physiological processes. Since fluorescence, absorbance change and spectral reflectance are non-invasive measurements that may be used as indicators for assessing drought tolerance in medicinal plants.

Diversity of Phytosterols in Leaves of Wild Brassicaceae Species as Compared to Brassica napus Cultivars: Potential Traits for Insect Resistance and Abiotic Stress Tolerance

Phytosterols are natural compounds found in all higher plants that have a wide variety of roles in plant growth regulation and stress tolerance. The phytosterol composition can also influence the development and reproductive rate of strict herbivorous insects and other important agronomic traits such as temperature and drought tolerance in plants. In this study, we analysed the phytosterol composition in 18 Brassica napus (Rapeseed/canola) cultivars and 20 accessions belonging to 10 related wild Brassicaceae species to explore diverse and novel phytosterol profiles. Plants were grown in a controlled phytotron environment and their phytosterols were analysed using a saponification extraction method followed by GC-MS from the leaf samples. The B. napus cultivars showed slight diversity in eight phytosterols (>0.02%) due to the genotypic effect, whereas the wild accessions showed significant variability in their phytosterol profiles. Of interest, a number of wild accessions were found with high levels of campesterol (HIN20, HIN23, HUN27, HIN30, SARS2, and UPM6563), stigmasterol (UPM6813, UPM6563, ALBA17, and ALBA2), and isofucosterol (SARS12, SAR6, and DMU2). These changes in individual phytosterols, or ratios of phytosterols, can have a significant implication in plant tolerance to abiotic stress and plant insect resistance properties, which can be used in breeding for crop improvement.

Phytoremediation potential of Solanum viarum Dunal and functional aspects of their capitate glandular trichomes in lead, cadmium, and zinc detoxification

In the present scenario, remediation of heavy metals (HMs) contaminated soil has become an important work to be done for the well-being of human and their environment. Phytoremediation can be regarded as an excellent method in environmental technologies. The present contemporary research explores the Solanum viarum Dunal function as a potential accumulator of hazardous HMs viz. lead (Pb), cadmium (Cd), zinc (Zn), and their combination (CHM). On toxic concentrations of Pb, Cd, Zn, and their synergistic exposure, seeds had better germination percentage and their 90d old aerial tissues accumulated Pb, Cd, and Zn concentrations ranging from 44.53, 84.06, and 147.29 mg kg^-1 DW, respectively. Pattern of accumulation in roots was as Zn 70.08 > Pb 48.55 > Cd 42.21 mg kg^-1DW. Under HMs treatment, positive modulation in physiological performances, antioxidant activities suggested an enhanced tolerance along with higher membrane stability due to increased levels of lignin, proline, and sugar. Phenotypic variations were recorded in prickles and roots of 120 d old HM stressed plants, which are directly correlated with better acclimation. Interestingly, trichomes of the plant also showed HM accumulation. Later, SEM-EDX microanalysis suggested involvement of S. viarum capitate glandular trichomes as excretory organs for Cd and Zn. Thus, the present study provides an understanding of the mechanism that makes S. viarum to function as potent accumulator and provides information to generate plants to be used for phytoremediation.

Crop Root Responses to Drought Stress: Molecular Mechanisms, Nutrient Regulations, and Interactions with Microorganisms in the Rhizosphere

Roots play important roles in determining crop development under drought. Under such conditions, the molecular mechanisms underlying key responses and interactions with the rhizosphere in crop roots remain limited compared with model species such as Arabidopsis. This article reviews the molecular mechanisms of the morphological, physiological, and metabolic responses to drought stress in typical crop roots, along with the regulation of soil nutrients and microorganisms to these responses. Firstly, we summarize how root growth and architecture are regulated by essential genes and metabolic processes under water-deficit conditions. Secondly, the functions of the fundamental plant hormone, abscisic acid, on regulating crop root growth under drought are highlighted. Moreover, we discuss how the responses of crop roots to altered water status are impacted by nutrients, and vice versa. Finally, this article explores current knowledge of the feedback between plant and soil microbial responses to drought and the manipulation of rhizosphere microbes for improving the resilience of crop production to water stress. Through these insights, we conclude that to gain a more comprehensive understanding of drought adaption mechanisms in crop roots, future studies should have a network view, linking key responses of roots with environmental factors.

Genetic modification of Gossypium arboreum universal stress protein (GUSP1) improves drought tolerance in transgenic cotton (Gossypium hirsutum)

Cotton crop suffers shortage of irrigation water at reproductive stage which reduces the yield and fibre quality. Universal stress proteins belong to Pfam00582 which enables several plants to cope with multiple stresses via ATP binding. GUSP1 (Gossypium arboreum USP) is one of such proteins; its amino acids were mutated after in silico simulations including homology modeling and molecular docking analysis. Transgenic cotton plants were developed through Agrobacterium mediated genetic transformation by using mutated pmGP1 and non mutated pGP1 constructs under CaMV35S promoter. PCR and semi-quantitative PCR analyses confirmed the amplification and expression of transgene in transgenic plants. It was revealed that leaf relative water content, total chlorophyll content, CO₂ assimilation as net photosynthesis, stomatal conductance, total soluble sugars and proline content was significantly increased at P ≤ 0.0001 and P ≤ 0.001 in both the pmGP1 and pGP1 transgenic plants as compared to non transgenic control plants. Moreover, relative membrane permeability and the transpiration rate were reduced significantly at P ≤ 0.0001 and P ≤ 0.001 respectively in transgenic plants under drought stress. Furthermore, the T1 transgenic seedlings containing pmGP1 mutated construct showed longer roots under desiccation stress imposed by 5% PEG. Transgene inheritance into the T1 progeny plants was confirmed by amplification through PCR and integration through Southern blot. Hence, our results pave the way to utilize the mutagenized known genes for increasing endurance of plants under drought stress. This will help to increase our understanding of drought tolerance/ sensitivity in cotton plants at the molecular level.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01048-5.

Towards doubling fibre yield for cotton in the semiarid agricultural area by increasing tolerance to drought, heat and salinity simultaneously

Abiotic stresses such as extreme temperatures, water-deficit and salinity negatively affect plant growth and development, and cause significant yield losses. It was previously shown that co-overexpression of the Arabidopsis vacuolar pyrophosphatase gene AVP1 and the rice SUMO E3 ligase gene OsSIZ1 in Arabidopsis significantly increased tolerance to multiple abiotic stresses and led to increased seed yield for plants grown under single or multiple abiotic stress conditions. It was hypothesized that there might be synergistic effects between AVP1 overexpression and OsSIZ1 overexpression, which could lead to substantially increased yields if these two genes are co-overexpressed in real crops. To test this hypothesis, AVP1 and OsSIZ1 were co-overexpressed in cotton, and the impact of OsSIZ1/AVP1 co-overexpression on cotton's performance under normal growth and multiple stress conditions were analysed. It was found that OsSIZ1/AVP1 co-overexpressing plants performed significantly better than AVP1-overexpressing, OsSIZ1-overexpressing and wild-type cotton plants under single, as well as under multiple stress conditions in laboratory and field conditions. Two field studies showed that OsSIZ1/AVP1 co-overexpressing plants produced 133% and 81% more fibre than wild-type cotton in the dryland conditions of West Texas. This research illustrates that co-overexpression of AVP1 and OsSIZ1 is a viable strategy for engineering abiotic stress-tolerant crops and could substantially improve crop yields in low input or marginal environments, providing a solution for food security for countries in arid and semiarid regions of the world.

Morpho-physiological and molecular characterization of drought tolerance traits in Gossypium hirsutum genotypes under drought stress

Drought stress is one of the major abiotic stresses affecting lint yield and fibre quality in cotton. With increase in population, degrading natural resources and frequent drought occurrences, development of high yielding, drought tolerant cotton cultivars is critical for sustainable cotton production across countries. Six Gossypium hirsutum genotypes identified for drought tolerance, wider adaptability and better fibre quality traits were characterized for various morpho-physiological and biochemical characters and their molecular basis was investigated under drought stress. Under drought conditions, genotypes revealed statistically significant differences for all the morpho-physiological and biochemical traits. The interaction (genotype × treatment) effects were highly significant for root length, excised leaf water loss and cell membrane thermostability indicating differential interaction of genotypes under control and stress conditions. Correlation studies revealed that under drought stress, relative water content had significant positive correlation with root length and root-to-shoot ratio while it had significant negative correlation with excised leaf water loss, epicuticular wax, proline, potassium and total soluble sugar content. Analysis of expression of fourteen drought stress related genes under water stress indicated that both ABA dependent and ABA independent mechanisms of drought tolerance might be operating differentially in the studied genotypes. IC325280 and LRA5166 exhibited ABA mediated expression of stress responsive genes and traits. Molecular basis of drought tolerance in IC357406, Suraj, IC259637 and CNH 28I genotypes could be attributed to ABA independent pathway. Based on physiological phenotyping, the genotypes IC325280 and IC357406 were identified to possess better root traits and LRA5166 was found to have enhanced cellular level tolerance. Variety Suraj exhibited good osmotic adjustment and better root traits to withstand water stress. The identified drought component trait(s) in specific genotypes would pave way for their pyramiding through marker assisted cotton breeding.

Quantitative proteomics analysis reveals resistance differences of banana cultivar 'Brazilian' to Fusarium oxysporum f. sp. cubense races 1 and 4

Banana Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense (Foc), is one of the most devastating diseases in banana production. Foc is classified into three physiological races. However, the resistance mechanisms of banana against different Foc races are poorly understood. In this study, we performed a comparative proteomics analysis to investigate the resistance mechanisms of 'Brazilian' against Foc1 and Foc4. The proteomes of 'Brazilian' roots inoculated with Foc1 and Foc4 and mock inoculated control at 48 h were analyzed using TMT based quantitative analysis technique. A total of 7325 unique protein species were identified, of which 689, 744, and 1222 protein species were differentially accumulated in Foc1 vs. CK, Foc4 vs. CK, and Foc1 vs. Foc4, respectively. The differential accumulations of candidate protein species were further confirmed by RT-qPCR, PRM, and physiological and biochemical assays. Bioinformatics analysis revealed that the differentially abundance protein species (DAPS) related to pattern recognition receptors, plant cell wall modification, redox homeostasis, and defense responses were differentially accumulated after Foc1 and Foc4 infection, suggesting that 'Brazilian' differed in resistance to the two Foc races. Our study lay the foundation for an in-depth understanding of the interaction between bananas and Foc at the proteome level. SIGNIFICANCE: The banana fusarium wilt disease is one of the most destructive disease of banana and is caused by Fusarium oxysporum f. sp. cubense (Foc). Foc is classified into three physiological races, namely, Foc1, Foc2, and Foc4. Among these races, Foc1 and Foc4 are widely distributed in south China and significantly lose yield. Although both physiological races (Foc1 and Foc4) can invade the Cavendish banana cultivar 'Brazilian', they have significant pathogenicity differences. Unfortunately, how the resistance differences are produced between two races is still largely unclear to date. In this study, we addressed this issue by performing TMT-based comparative quantitative proteomics analysis of 'Brazilian' roots after inoculation with Foc1 and Foc4 as well as sterile water as the control. We revealed that the series of protein species associated with pattern recognition receptors, plant cell wall modification, redox homeostasis, pathogenesis, phytohormones and signal transduction, plant secondary metabolites and programmed cell death etc. were involved in the response to Foc infection. Notably, the potential role of lipid signaling in banana defense against Foc are not reported previously but rather unveiled for the first time in this study. The current study represents the most extensive analysis of the protein profile of 'Brazilian' in response to Foc inoculation and includes for the first time the results from comparison quantitative proteomics analysis between plants inoculated with a pathogenic strain Foc4 and a nonpathogenic strain Foc1 of 'Brazilian', which will lay the foundation for an in-depth understanding of the interaction between bananas and Foc at the proteome level.

Whole Genome Analysis of Cyclin Dependent Kinase (CDK) Gene Family in Cotton and Functional Evaluation of the Role of CDKF4 Gene in Drought and Salt Stress Tolerance in Plants

Cotton (Gossypium spp.) is the number one crop cultivated for fiber production and the cornerstone of the textile industry. Drought and salt stress are the major abiotic stresses, which can have a huge economic impact on cotton production; this has been aggravated with continued climate change, and compounded by pollution. Various survival strategies evolved by plants include the induction of various stress responsive genes, such as cyclin dependent kinases (CDKs). In this study, we performed a whole-genome identification and analysis of the CDK gene family in cotton. We identified 31, 12, and 15 CDK genes in G. hirsutum, G. arboreum, and G. raimondii respectively, and they were classified into 6 groups. CDK genes were distributed in 15, 10, and 9 linkage groups of AD, D, and A genomes, respectively. Evolutionary analysis revealed that segmental types of gene duplication were the primary force underlying CDK genes expansion. RNA sequence and RT-qPCR validation revealed that Gh_D12G2017 (CDKF4) was strongly induced by drought and salt stresses. The transient expression of Gh_D12G2017-GFP fusion protein in the protoplast showed that Gh_D12G2017 was localized in the nucleus. The transgenic Arabidopsis lines exhibited higher concentration levels of the antioxidant enzymes measured, including peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) concentrations under drought and salt stress conditions with very low levels of oxidants. Moreover, cell membrane stability (CMS), excised leaf water loss (ELWL), saturated leaf weight (SLW), and chlorophyll content measurements showed that the transgenic Arabidopsis lines were highly tolerant to either of the stress factors compared to their wild types. Moreover, the expression of the stress-related genes was also significantly up-regulated in Gh_D12G2017(CDKF4) transgenic Arabidopsis plants under drought and salt conditions. We infer that CDKF-4s and CDKG-2s might be the primary regulators of salt and drought responses in cotton.

Bacterial endophytes modulates the withanolide biosynthetic pathway and physiological performance in Withania somnifera under biotic stress

Despite the vast exploration of endophytic microbes for growth enhancement in various crops, knowledge about their impact on the production of therapeutically important secondary metabolites is scarce. In the current investigation, chitinolytic bacterial endophytes were isolated from selected medicinal plants and assessed for their mycolytic as well as plant growth promoting potentials. Among them the two most efficient bacterial endophytes namely Bacillus amyloliquefaciens (MPE20) and Pseudomonas fluorescens (MPE115) individually as well as in combination were able to modulate withanolide biosynthetic pathway and tolerance against Alternaria alternata in Withania somnifera. Interestingly, the expression level of withanolide biosynthetic pathway genes (3-hydroxy-3-methylglutaryl co-enzyme A reductase, 1-deoxy-D-xylulose-5-phosphate reductase, farnesyl di-phosphate synthase, squalene synthase, cytochrome p450, sterol desaturase, sterol Δ-7 reductase and sterol glycosyl transferases) were upregulated in plants treated with the microbial consortium under A. alternata stress. In addition, application of microbes not only augmented withaferin A, withanolide A and withanolide B content (1.52-1.96, 3.32-5.96 and 12.49-21.47 fold, respectively) during A. alternata pathogenicity but also strengthened host resistance via improvement in the photochemical efficiency, normalizing the oxidized and non-oxidized fraction, accelerating photochemical and non-photochemical quantum yield, and electron transport rate. Moreover, reduction in the passively dissipated energy of PSI and PSII in microbial combination treated plants corroborate well with the above findings. Altogether, the above finding highlights novel insights into the underlying mechanisms in application of endophytes and emphasizes their capability to accelerate biosynthesis of withanolides in W. somnifera under biotic stress caused by A. alternata.

RNA-seq analysis reveals alternative splicing under salt stress in cotton, Gossypium davidsonii

BACKGROUND

Numerous studies have focused on the regulation of gene expression in response to salt stress at the transcriptional level; however, little is known about this process at the post-transcriptional level.

RESULTS

Using a diploid D genome wild salinity-tolerant cotton species, Gossypium davidsonii, we analyzed alternative splicing (AS) of genes related to salt stress by comparing high-throughput transcriptomes from salt-treated and well-watered roots and leaves. A total of 14,172 AS events were identified involving 6798 genes, of which intron retention (35.73%) was the most frequent, being detected in 3492 genes. Under salt stress, 1287 and 1228 differential alternative splicing (DAS) events were identified in roots and leaves, respectively. These DAS genes were associated with specific functional pathways, such as "responses to stress", "metabolic process" and "RNA splicing", implying that AS represents an important pathway of gene regulation in response to salt stress. Several salt response genes, such as pyrroline-5-carboxylate synthase (P5CS), K⁺ channel outward (KCO1), plasma membrane intrinsic protein (PIP) and WRKY33 which were involved in osmotic balance, ion homeostasis, water transportation and transcriptional regulation, respectively, were identified with differential alternative splicing under salt stress. Moreover, we revealed that 13 genes encoding Ser/Arg-rich (SR) proteins related to AS regulation were differentially alternatively spliced under salt stress.

CONCLUSION

This study first provide a comprehensive view of AS in G. davidsonii, and highlight novel insights into the potential roles of AS in plant responses to salt stress.

Physiological performance of two contrasting rice varieties under water stress

Two rice varieties PR-115 and Super-7 were imposed to water stress and different physiological traits were monitored to evaluate the performance of these varieties under drought. Under water stress condition although the relative water content, osmotic potential, chlorophyll content, photosynthesis rate, carbon discrimination and biomass decreased in both the varieties however, the reduction was more pronounced in Super-7 variety. Oryzanol a trans-ester of ferulic acid functions as antioxidant and it increased along with total phenolic and anthocyanin content in both the varieties under drought stress. However, gallic acid, 4 hydroxy benzoic acid, syringic acid and chlorogenic acid showed differential pattern in both of the varieties under water limiting conditions. Under drought, grain yield was penalized by 17 and 54% in PR-115 and Super-7 varieties, respectively in comparison to watered plants. Super-7 variety showed pronounced electrolyte leakage and MDA enhancement under water stress condition. High non photochemical quenching and reduction in Y(NO) and Y(II) indicated balanced energy management in tolerant PR-115 variety. The studies showed that PR-115 is a drought tolerant variety while Super-7 is drought sensitive in nature.