Effects of drought stress on photosynthetic physiological characteristics, leaf microstructure, and related gene expression of yellow horn

Morpho-Physiological Traits and Oil Quality in Drought-Tolerant Raphanus sativus L. Used for Biofuel Production

Raphanus sativus L. is a potential source of raw material for biodiesel fuel due to the high oil content in its grains. In Brazil, this species is cultivated in the low rainfall off-season, which limits the productivity of the crop. The present study investigated the effects of water restriction on the physiological and biochemical responses, production components, and oil quality of R. sativus at different development stages. The treatments consisted of 100% water replacement (control), 66%, and 33% of field capacity during the phenological stages of vegetative growth, flowering, and grain filling. We evaluated characteristics of water relations, gas exchange, chlorophyll a fluorescence, chloroplast pigment, proline, and sugar content. The production components and chemical properties of the oil were also determined at the end of the harvest cycle. Drought tolerance of R. sativus was found to be mediated primarily during the vegetative growth stage by changes in photosynthetic metabolism, stability of photochemical efficiency, increased proline concentrations, and maintenance of tissue hydration. Grain filling was most sensitive to water limitation and showed a reduction in yield and oil content. However, the chemical composition of the oil was not altered by the water deficit. Our data suggest that R. sativus is a drought-tolerant species.

Limitations of Plant Stress Tolerance upon Heat and CO2 Exposure in Black Poplar: Assessment of Photosynthetic Traits and Stress Volatile Emissions

Volatile organic compounds (VOCs) emitted by plants may help in understanding the status of a plant's physiology and its coping with mild to severe stress. Future climatic projections reveal that shifts in temperature and CO2 availability will occur, and plants may incur the uncoupling of carbon assimilation and synthesis of key molecules. This study explores the patterns of emissions of key VOCs (isoprene, methanol, acetaldehyde, and acetic acid) emitted by poplar leaves (more than 350) under a combined gradient of temperature (12-42 °C) and air CO2 concentration (400-1500 ppm), along with measurements of photosynthetic rates and stomatal conductance. Isoprene emission exhibited a rise with temperature and CO2 availability, peaking at 39 °C, the temperature at which methanol emission started to peak, illustrating the limit of stress tolerance to severe damage. Isoprene emission was uncoupled from the photosynthesis rate, indicating a shift from the carbon source for isoprene synthesis, while assimilation was decreased. Methanol and acetaldehyde emissions were correlated with stomatal conductance and peaked at 25 °C and 1200 ppm CO2. Acetic acid emissions lacked a clear correlation with stomatal conductance and the emission pattern of its precursor acetaldehyde. This study offers crucial insights into the limitations of photosynthetic carbon and stress tolerance.

Transcriptomic profiling of Poa pratensis L. under treatment of various phytohormones

Poa pratensis L. (Poaceae) is a valuable grass across the north hemisphere, inhabiting diverse environments with wide altitudinal span, where ubiquitous various kinds of stresses. Phytohormones would be helpful to improve tolerance to abiotic and biotic stresses, but the responses of transcriptome regulation of P. pratensis to exogenous phytohormones application remain unclear. In this study, we explored the alteration of plant physiological responses by the application of phytohormones. Aiming to achieve this knowledge, we got full-length transcriptome data 42.76 Gb, of which 74.9% of transcripts were completed. Then used 27 samples representing four treatments conducted at two time points (1 h and 6 h after application) to generate RNA-seq data. 371 and 907 common DEGs were identified in response to four phytohormones application, respectively, these DEGs were involved in "plant hormone signal transduction", "carbon metabolism" and "plant-pathogen interaction". Finally, P. pratensis basic research can gain valuable information regarding the responses to exogenous application of phytohormones in physiological indicators and transcriptional regulations in order to facilitate the development of new cultivars.

Histone deacetylase 9 interacts with SiHAT3.1 and SiHDA19 to repress dehydration responses through H3K9 deacetylation in foxtail millet

Climate change inflicts several stresses on plants, of which dehydration stress severely affects growth and productivity. C4 plants possess better adaptability to dehydration stress; however, the role of epigenetic modifications underlying this trait is unclear. In particular, the molecular links between histone modifiers and their regulation remain elusive. In this study, genome-wide H3K9 acetylation (H3K9ac) enrichment using ChIP-sequencing was performed in two foxtail millet cultivars with contrasting dehydration tolerances (IC403579, cv. IC4-tolerant, and IC480117, cv. IC41-sensitive). It revealed that a histone deacetylase, SiHDA9, was significantly up-regulated in the sensitive cultivar. Further characterization indicated that SiHDA9 interacts with SiHAT3.1 and SiHDA19 to form a repressor complex. SiHDA9 might be recruited through the SiHAT3.1 recognition sequence onto the upstream of dehydration-responsive genes to decrease H3K9 acetylation levels. The silencing of SiHDA9 resulted in the up-regulation of crucial genes, namely, SiRAB18, SiRAP2.4, SiP5CS2, SiRD22, SiPIP1;4, and SiLHCB2.3, which imparted dehydration tolerance in the sensitive cultivar (IC41). Overall, the study provides mechanistic insights into SiHDA9-mediated regulation of dehydration stress response in foxtail millet.

Drought stress in Lens culinaris: effects, tolerance mechanism, and its smart reprogramming by using modern biotechnological approaches

Among legumes, lentil serves as an imperative source of dietary proteins and are considered an important pillar of global food and nutritional security. The crop is majorly cultivated in arid and semi-arid regions and exposed to different abiotic stresses. Drought stress is a polygenic stress that poses a major threat to the crop productivity of lentils. It negatively influenced the seed emergence, water relations traits, photosynthetic machinery, metabolites, seed development, quality, and yield in lentil. Plants develop several complex physiological and molecular protective mechanisms for tolerance against drought stress. These complicated networks are enabled to enhance the cellular potential to survive under extreme water-scarce conditions. As a result, proper drought stress-mitigating novel and modern approaches are required to improve lentil productivity. The currently existing biotechnological techniques such as transcriptomics, genomics, proteomics, metabolomics, CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/cas9), and detection of QTLs (quantitative trait loci), proteins, and genes responsible for drought tolerance have gained appreciation among plant breeders for developing climate-resilient lentil varieties. In this review, we critically elaborate the impact of drought on lentil, mechanisms employed by plants to tolerate drought, and the contribution of omics approaches in lentils for dealing with drought, providing deep insights to enhance lentil productivity and improve resistance against abiotic stresses. We hope this updated review will directly help the lentil breeders to develop resistance against drought stress.

Graphical Abstract

Full-length transcriptome and RNA-Seq analyses reveal the resistance mechanism of sesame in response to Corynespora cassiicola

BACKGROUND

Corynespora leaf spot is a common leaf disease occurring in sesame, and the disease causes leaf yellowing and even shedding, which affects the growth quality of sesame. At present, the mechanism of sesame resistance to this disease is still unclear. Understanding the resistance mechanism of sesame to Corynespora leaf spot is highly important for the control of infection. In this study, the leaves of the sesame resistant variety (R) and the sesame susceptible variety (S) were collected at 0-48 hpi for transcriptome sequencing, and used a combined third-generation long-read and next-generation short-read technology approach to identify some key genes and main pathways related to resistance.

RESULTS

The gene expression levels of the two sesame varieties were significantly different at 0, 6, 12, 24, 36 and 48 hpi, indicating that the up-regulation of differentially expressed genes in the R might enhanced the resistance. Moreover, combined with the phenotypic observations of sesame leaves inoculated at different time points, we found that 12 hpi was the key time point leading to the resistance difference between the two sesame varieties at the molecular level. The WGCNA identified two modules significantly associated with disease resistance, and screened out 10 key genes that were highly expressed in R but low expressed in S, which belonged to transcription factors (WRKY, AP2/ERF-ERF, and NAC types) and protein kinases (RLK-Pelle_DLSV, RLK-Pelle_SD-2b, and RLK-Pelle_WAK types). These genes could be the key response factors in the response of sesame to infection by Corynespora cassiicola. GO and KEGG enrichment analysis showed that specific modules could be enriched, which manifested as enrichment in biologically important pathways, such as plant signalling hormone transduction, plant-pathogen interaction, carbon metabolism, phenylpropanoid biosynthesis, glutathione metabolism, MAPK and other stress-related pathways.

CONCLUSIONS

This study provides an important resource of genes contributing to disease resistance and will deepen our understanding of the regulation of disease resistance, paving the way for further molecular breeding of sesame.

Photosynthetic mechanisms underlying NaCl-induced salinity tolerance in rice (Oryza sativa)

BACKGROUND

Salinity stress is an environmental constraint that normally develops concurrently under field conditions, resulting in drastic limitation of rice plant growth and grain productivity. The objective of this study was to explore the alleviating effects of NaCl pre-treatment on rice seedlings as well as the salt tolerance mechanisms by evaluating morph-physiological traits.

RESULTS

Variety Huanghuazhan, either soaked in distilled water or 25 mg/L Prohexadione calcium (Pro-Ca), were first hardened with varying concentrations of NaCl solutions (0 and 50 mM NaCl), and then subjected to varying degrees of salt stress (0 and 100 mM NaCl), indicated by S0, S1, S2 and S3, respectively. Growth analysis suggested that NaCl-pretreatment improved the root/shoot ratio in water-soaked rice plant at DAP 0. Data related to the reaction center density, photosynthetic electron transport efficiency, trapping efficiency were compared before (CK) using performance Index (PIabs). Compared to S2 (Pro-Ca-S2) treatment, PIabs did not show any difference with plants pre-treated with NaCl (S3 or Pro-Ca-S3). Rather than PIabs, significant difference was found in photosynthetic electron transport efficiency (ΨEo). The ΨEo value in Pro-S2 was significantly lowered as compared to Pro-S3 treatment at DAP 7, and the decrease rate was about 6.5%. Correlation analysis indicated leaf PIabs was weak correlated with plant biomass while the quantum yield for reduction of the PSI end electron acceptors, trapped energy flux per reaction center and PSII antenna size displayed strong positive correlation with biomass. Additional analysis revealed that 100 mM NaCl significantly reduced leaf linear electron flux under low-light conditions, regardless of whether seedlings had been pre-treated with 50 mM NaCl or not.

CONCLUSIONS

NaCl-induced salt tolerance was related to the robust photosynthetic machinery.