Beat the heat: plant- and microbe-mediated strategies for crop thermotolerance

Effects of high-temperature stress on gene expression related to photosynthesis in two jujube (Ziziphus jujuba Mill.) varieties

Elevated temperatures critically impact crop growth, development, and yield, with photosynthesis being the most temperature-sensitive physiological process in plants. This study focused on assessing the photosynthetic response and genetic adaptation of two different heat-resistant jujube varieties 'Junzao' (J) and 'Fucuimi' (F), to high-temperature stress (42°C Day/30°C Night). Comparative analyses of leaf photosynthetic indices, microstructural changes, and transcriptome sequencing were conducted. Results indicated superior high-temperature adaptability in F, evidenced by alterations in leaf stomatal behavior - particularly in J, where defense cells exhibited significant water loss, shrinkage, and reduced stomatal opening, alongside a marked increase in stomatal density. Through transcriptome sequencing 13,884 differentially expressed genes (DEGs) were identified, significantly enriched in pathways related to plant-pathogen interactions, amino acid biosynthesis, starch and sucrose metabolism, and carbohydrate metabolism. Key findings include the identification of photosynthetic pathway related DEGs and HSFA1s as central regulators of thermal morphogenesis and heat stress response. Revealing their upregulation in F and downregulation in J. The results indicate that these genes play a crucial role in improving heat tolerance in F. This study unveils critical photosynthetic genes involved in heat stress, providing a theoretical foundation for comprehending the molecular mechanisms underlying jujube heat tolerance.

The MdHSC70-MdWRKY75 module mediates basal apple thermotolerance by regulating the expression of heat shock factor genes

Heat stress severely restricts the growth and fruit development of apple (Malus domestica). Little is known about the involvement of WRKY proteins in the heat tolerance mechanism in apple. In this study, we found that the apple transcription factor (TF) MdWRKY75 responds to heat and positively regulates basal thermotolerance. Apple plants that overexpressed MdWRKY75 were more tolerant to heat stress while silencing MdWRKY75 caused the opposite phenotype. RNA-seq and reverse transcription quantitative PCR showed that heat shock factor genes (MdHsfs) could be the potential targets of MdWRKY75. Electrophoretic mobility shift, yeast one-hybrid, β-glucuronidase, and dual-luciferase assays showed that MdWRKY75 can bind to the promoters of MdHsf4, MdHsfB2a, and MdHsfA1d and activate their expression. Apple plants that overexpressed MdHsf4, MdHsfB2a, and MdHsfA1d exhibited heat tolerance and rescued the heat-sensitive phenotype of MdWRKY75-Ri3. In addition, apple heat shock cognate 70 (MdHSC70) interacts with MdWRKY75, as shown by yeast two-hybrid, split luciferase, bimolecular fluorescence complementation, and pull-down assays. MdHSC70 acts as a negative regulator of the heat stress response. Apple plants that overexpressed MdHSC70 were sensitive to heat, while virus-induced gene silencing of MdHSC70 enhanced heat tolerance. Additional research showed that MdHSC70 exhibits heat sensitivity by interacting with MdWRKY75 and inhibiting MdHsfs expression. In summary, we proposed a mechanism for the response of apple to heat that is mediated by the "MdHSC70/MdWRKY75-MdHsfs" molecular module, which enhances our understanding of apple thermotolerance regulated by WRKY TFs.

LzSCL9, a Novel GRAS Transcription Factor in Lanzhou Lily (Lilium davidii var. unicolor), Participates in Regulation of Trichokonins-Primed Heat Stress Tolerance

In our previous research, we found that trichokonins' (TKs) employment improved the thermotolerance of the Lanzhou lily, a renowned edible crop species endemic to China that is relatively susceptible to high temperatures (HTs). Here, a novel Lanzhou lily GRAS gene, LzSCL9, was identified to respond to heat stress (HS) and HS+TKs treatment based on transcriptome and RT-qPCR analysis. TKs could improve the upregulation of LzSCL9 during long-term HS. The expression profile of LzSCL9 in response to HS with or without TKs treatment showed a significant positive correlation with LzHsfA2a-1, which was previously identified as a key regulator in TKs' conferred resilience to HT. More importantly, overexpression of LzSCL9 in the lily enhanced its tolerance to HTs and silencing LzSCL9 in the lily reduced heat resistance. Taken together, this study identified the positive role of LzSCL9 in TK-induced thermotolerance, thereby preliminarily establishing a molecular mechanism on TKs regulating the thermostability of the Lanzhou lily and providing a new candidate regulator for plant heat-resistant breeding.

Interactions between root endophytic microorganisms and the reduced negative ion release capacity of Phalaenopsis aphrodite Rchb. f. under high temperature stress

Introduction

Negative oxygen ions are produced by plants through photosynthesis, utilizing "tip discharge" or the photoelectric effect, which has various functions such as sterilization, dust removal, and delaying aging. With global warming, high temperatures may affect the ability of Phalaenopsis aphrodite Rchb. f. to produce negative oxygen ions. P. aphrodite is commonly used in modern landscape planning and forest greening.

Methods

In this study, P. aphrodite was selected as the research object. By artificially simulating the climate, the control group (CK) and the high temperature stress group (HS) were set up in the experiment.

Results

The study found that compared with the control group, the ability of P. aphrodite to produce negative oxygen ions significantly decreased when exposed to high temperature stress. Meanwhile, under high temperature stress treatment, peroxidase content increased by 102%, and proline content significantly increased by 35%.

Discussion

Redundancy analysis results indicated a significant correlation between the root endophytic microbial community of P. aphrodite and negative oxygen ions, as well as physiological indicators. Under high temperature stress, P. aphrodite may affect the regulation of physiological indicators by modifying the composition of root endophytic microbial communities, thereby influencing the ability to release negative oxygen ions.

Microbe-induced coordination of plant iron-sulfur metabolism enhances high-light-stress tolerance of Arabidopsis

High-light stress strongly limits agricultural production in subtropical and tropical regions owing to photo-oxidative damage, decreased growth, and decreased yield. Here, we investigated whether beneficial microbes can protect plants under high-light stress. We found that Enterobacter sp. SA187 (SA187) supports the growth of Arabidopsis thaliana under high-light stress by reducing the accumulation of reactive oxygen species and maintaining photosynthesis. Under high-light stress, SA187 triggers dynamic changes in the expression of Arabidopsis genes related to fortified iron metabolism and redox regulation, thereby enhancing the antioxidative glutathione/glutaredoxin redox system of the plant. Genetic analysis showed that the enhancement of iron and sulfur metabolism by SA187 is coordinated by ethylene signaling. In summary, beneficial microbes could be an effective and inexpensive means of enhancing high-light-stress tolerance in plants.

Early signaling enhance heat tolerance in Arabidopsis through modulating jasmonic acid synthesis mediated by HSFA2

Given the detrimental impact of global warming on crop production, it is particularly important to understand how plants respond and adapt to higher temperatures. Using the non-invasive micro-test technique and laser confocal microscopy, we found that the cascade process of early signals (K+, H2O2, H+, and Ca2+) ultimately resulted in an increase in the cytoplasmic Ca2+ concentration when Arabidopsis was exposed to heat stress. Quantitative real-time PCR demonstrated that heat stress significantly up-regulated the expression of CAM1, CAM3 and HSFA2; however, after CAM1 and CAM3 mutation, the upregulation of HSFA2 was reduced. In addition, heat stress affected the expression of LOX3 and OPR3, which was not observed when HSFA2 was mutated. Luciferase reporter gene expression assay and electrophoretic mobility shift assay showed that HSFA2 regulated the expression of both genes. Determination of jasmonic acid (JA) content showed that JA synthesis was promoted by heat stress, but was damaged when HSFA2 and OPR3 were mutated. Finally, physiological experiments showed that JA reduced the relative electrical conductivity of leaves, enhanced chlorophyll content and relative water content, and improved the survival rate of Arabidopsis under heat stress. Together, our results reveal a new pathway for Arabidopsis to sense and transmit heat signals; HSFA2 is involved in the JA synthesis, which can act as a defensive compound improving Arabidopsis heat tolerance.

Transcription factor CaHDZ15 promotes pepper basal thermotolerance by activating HEAT SHOCK FACTORA6a

High temperature stress (HTS) is a serious threat to plant growth and development and to crop production in the context of global warming, and plant response to HTS is largely regulated at the transcriptional level by the actions of various transcription factors (TFs). However, whether and how homeodomain-leucine zipper (HD-Zip) TFs are involved in thermotolerance are unclear. Herein, we functionally characterized a pepper (Capsicum annuum) HD-Zip I TF CaHDZ15. CaHDZ15 expression was upregulated by HTS and abscisic acid in basal thermotolerance via loss- and gain-of-function assays by virus-induced gene silencing in pepper and overexpression in Nicotiana benthamiana plants. CaHDZ15 acted positively in pepper basal thermotolerance by directly targeting and activating HEAT SHOCK FACTORA6a (HSFA6a), which further activated CaHSFA2. In addition, CaHDZ15 interacted with HEAT SHOCK PROTEIN 70-2 (CaHsp70-2) and glyceraldehyde-3-phosphate dehydrogenase1 (CaGAPC1), both of which positively affected pepper thermotolerance. CaHsp70-2 and CaGAPC1 promoted CaHDZ15 binding to the promoter of CaHSFA6a, thus enhancing its transcription. Furthermore, CaHDZ15 and CaGAPC1 were protected from 26S proteasome-mediated degradation by CaHsp70-2 via physical interaction. These results collectively indicate that CaHDZ15, modulated by the interacting partners CaGAPC1 and CaHsp70-2, promotes basal thermotolerance by directly activating the transcript of CaHSFA6a. Thus, a molecular linkage is established among CaHsp70-2, CaGAPC1, and CaHDZ15 to transcriptionally modulate CaHSFA6a in pepper thermotolerance.

Transcriptome and photosynthetic analyses provide new insight into the molecular mechanisms underlying heat stress tolerance in Rhododendron × pulchrum Sweet

Rhododendron species provide excellent ornamental use worldwide, yet heat stress (HS) is one of the major threats to their cultivation. However, the intricate mechanisms underlying the photochemical and transcriptional regulations associated with the heat stress response in Rhododendron remain relatively unexplored. In this study, the analyses of morphological characteristics and chlorophyll fluorescence (ChlF) kinetics showed that HS (40 °C/35 °C) had a notable impact on both the donor's and acceptor's sides of photosystem II (PSII), resulting in reduced PSII activity and electron transfer capacity. The gradual recovery of plants observed following a 5-day period of culture under normal conditions indicates the reversible nature of the HS impact on Rhododendron × pulchrum. Analysis of transcriptome data unveiled noteworthy trends: four genes associated with photosynthesis-antenna protein synthesis (LHCb1, LHCb2 and LHCb3) and the antioxidant system (glutamate-cysteine ligase) experienced significant down-regulation in the leaves of R. × pulchrum during HS. Conversely, aseorbate peroxidase and glutathione S-transferase TAU 8 demonstrated an up-regulated pattern. Furthermore, six down-regulated genes (phos-phoenolpyruvate carboxylase 4, sedoheptulose-bisphosphatase, ribose-5-phosphate isomerase 2, high cyclic electron flow 1, beta glucosidase 32 and starch synthase 2) and two up-regulated genes (beta glucosidase 2 and UDP-glucose pyrophosphorylase 2) implicated in photosynthetic carbon fixation and starch/sucrose metabolism were identified during the recovery process. To augment these insights, a weighted gene co-expression network analysis yielded a co-expression network, pinpointing the hub genes correlated with ChlF dynamics' variation trends. The cumulative results showed that HS inhibited the synthesis of photosynthesis-antenna proteins in R. × pulchrum leaves. This disruption subsequently led to diminished photochemical activities in both PSII and PSI, albeit with PSI exhibiting heightened thermostability. Depending on the regulation of the reactive oxygen species scavenging system and heat dissipation, photoprotection sustained the recoverability of R. × pulchrum to HS.

Molecular evolution and interaction of 14-3-3 proteins with H+-ATPases in plant abiotic stresses

Environmental stresses severely affect plant growth and crop productivity. Regulated by 14-3-3 proteins (14-3-3s), H+-ATPases (AHAs) are important proton pumps that can induce diverse secondary transport via channels and co-transporters for the abiotic stress response of plants. Many studies demonstrated the roles of 14-3-3s and AHAs in coordinating the processes of plant growth, phytohormone signaling, and stress responses. However, the molecular evolution of 14-3-3s and AHAs has not been summarized in parallel with evolutionary insights across multiple plant species. Here, we comprehensively review the roles of 14-3-3s and AHAs in cell signaling to enhance plant responses to diverse environmental stresses. We analyzed the molecular evolution of key proteins and functional domains that are associated with 14-3-3s and AHAs in plant growth and hormone signaling. The results revealed evolution, duplication, contraction, and expansion of 14-3-3s and AHAs in green plants. We also discussed the stress-specific expression of those 14-3-3and AHA genes in a eudicotyledon (Arabidopsis thaliana), a monocotyledon (Hordeum vulgare), and a moss (Physcomitrium patens) under abiotic stresses. We propose that 14-3-3s and AHAs respond to abiotic stresses through many important targets and signaling components of phytohormones, which could be promising to improve plant tolerance to single or multiple environmental stresses.

Root transcriptomic provides insights on molecular mechanisms involved in the tolerance to water deficit in Pisum sativum inoculated with Pseudomonas sp

MAIN CONCLUSION

Root transcriptomics and biochemical analyses in water-stressed Pisum sativum plants inoculated with Pseudomonas spp. suggested preservation of ABA-related pathway and ROS detoxification, resulting in an improved tolerance to stress. Drought already affects agriculture in large areas of the globe and, due to climate change, these areas are predicted to become increasingly unsuitable for agriculture. For several years, plant growth-promoting bacteria (PGPB) have been used to improve legume yields, but many aspects of this interaction are still unclear. To elucidate the mechanisms through which root-associated PGPB can promote plant growth in dry environments, we investigated the response of pea plants inoculated with a potentially beneficial Pseudomonas strain (PK6) and subjected to two different water regimes. Combined biometric, biochemical, and root RNA-seq analyses revealed that PK6 improved pea growth specifically under water deficit, as inoculated plants showed an increased biomass, larger leaves, and longer roots. Abscisic acid (ABA) and proline quantification, together with the transcriptome analysis, suggested that PK6-inoculated plant response to water deficit was more diversified compared to non-inoculated plants, involving alternative metabolic pathways for the detoxification of reactive oxygen species (ROS) and the preservation of the ABA stress signaling pathway. We suggest that the metabolic response of PK6-inoculated plants was more effective in their adaptation to water deprivation, leading to their improved biometric traits. Besides confirming the positive role that PGPB can have in the growth of a legume crop under adverse conditions, this study offers novel information on the mechanisms regulating plant-bacteria interaction under varying water availability. These mechanisms and the involved genes could be exploited in the future for the development of legume varieties, which can profitably grow in dry climates.

Multi-omics insights into the mechanism of the high-temperature tolerance in a thermotolerant Chlorella sorokiniana

Improving high-temperature tolerance of microalgae is crucial to enhance the robustness and economy of microalgae industrial production. Herein, a continuous adaptive laboratory evolution (ALE) system was developed to generate the thermotolerant strain of Chlorella sorokiniana. The resulting thermotolerant strain TR42 exhibited excellent cell growth and biomass production at 42 °C, the temperature that the original strain (OS) could not survive. The high-temperature resistant mechanism of TR42 was investigated by integrating the physiology, transcriptome, proteome and metabolome analyses, which involved enhancing antioxidant capacity, maintaining protein homeostasis, remodeling photosynthetic metabolism, and regulating the synthesis of heat-stress related metabolites. The proof-of-concept high-temperature outdoor cultivation demonstrated that TR42 exhibited 1.15- to 5.72-fold increases in biomass production and 1.62- to 7.04-fold increases in lipid productivity compared to those of OS, respectively, which provided a promising platform for microalgae industrial production. Thus, the multi-system thermotolerant mechanism of TR42 offered potential targets for enhancing high-temperature tolerance of microalgae.

CaRH57, a RNA helicase, contributes pepper tolerance to heat stress

RNA helicases (RHs) are required for most aspects of RNA metabolism and play an important role in plant stress tolerance. Heat stress (HS) causes the deleterious effects on plant cells, such as membrane disruption and protein misfolding, which results in the inhibition of plant growth and development. In this study, CaRH57 was identified from pepper (Capsicum annuum) and encodes a DEAD-box RH. CaRH57 was induced by HS, and overexpression of CaRH57 in Atrh57-1 rescued the glucose-sensitive phenotype of Atrh57-1, suggesting the functional replacement of CaRH57 to AtRH57. The nucleolus-localized CaRH57 possessed a RH activity in vitro. CaRH57 knockdown impaired pepper heat tolerance, showing severe necrosis and enhanced ROS accumulation in the region of the shoot tip. Additionally, accumulation of aberrant-spliced CaHSFA1d and CaHSFA9d was enhanced, and the corresponding mature mRNA levels were reduced in the TRV2 (Tobacco rattle virus)-CaRH57-infected plants compared with the control plants under HS. Overall, these results suggested that CaRH57 acted as a RH to confer pepper heat tolerance and was required for the proper pre-mRNA splicing of some HS-related genes.

Impact of PGPR inoculation on root morphological traits and root exudation in rapeseed and camelina: interactions with heat stress

Root exudation is involved in the recruitment of beneficial microorganisms by trophic relationships and/or signalling pathways. Among beneficial microorganisms, Plant Growth-Promoting Rhizobacteria (PGPR) are known to improve plant growth and stress resistance. These interactions are of particular importance for species that do not interact with mycorrhizal fungi, such as rapeseed (Brassica napus L.) and camelina (Camelina sativa (L.) Crantz). However, heat stress is known to have a quantitative and qualitative impact on root exudation and could affect the interactions between plants and PGPR. We aimed to analyse the effects of PGPR inoculation on root morphology and exudation in rapeseed and camelina at the reproductive stage. The modulation of the effects of these interactions under heat stress was also investigated. The plants were inoculated twice at the reproductive stage with two different Pseudomonas species and were exposed to heat stress after the second inoculation. In non-stressing conditions, after bacterial inoculation, rapeseed and camelina exhibited two contrasting behaviours in C root allocation. While rapeseed plants seemed to suffer from the interactions with the bacteria, camelina plants appeared to control the relationship with the PGPR by modifying the composition of their root exudates. Under heat stress, the plant-PGPR interaction was unbalanced for rapeseed, for which the C allocation strategy is mainly driven by the C cost from the bacteria. Alternatively, camelina plants prioritized C allocation for their own above-ground development. This work opens up new perspectives for understanding plant-PGPR interactions, especially in an abiotic stress context.

It is time to move: Heat-induced translocation events

Climate change-induced temperature fluctuations impact agricultural productivity through short-term intense heat waves or long-term heat stress. Plants have evolved sophisticated strategies to deal with heat stress. Understanding perception and transduction of heat signals from outside to inside cells is essential to improve plant thermotolerance. In this review, we will focus on translocation of molecules and proteins associated with signal transduction to understand how plant cells decode signals from the environment to trigger a suitable response.

Artificial warming affects sugar signals and flavonoid accumulation to improve female willows' growth faster than males

Increasing global warming is severely affecting tree growth and development. However, research on the sex-specific responses of dioecious trees to warming is scarce. Here, male and female Salix paraplesia were selected for artificial warming (an increase of 4 °C relative to ambient temperature) to investigate the effects on morphological, physiological, biochemical and molecular responses. The results showed that warming significantly promoted the growth of female and male S. paraplesia, but females grew faster than males. Warming affected photosynthesis, chloroplast structures, peroxidase activity, proline, flavonoids, nonstructural carbohydrates (NSCs) and phenolic contents in both sexes. Interestingly, warming increased flavonoid accumulation in female roots and male leaves but inhibited it in female leaves and male roots. The transcriptome and proteome results indicated that differentially expressed genes and proteins were significantly enriched in sucrose and starch metabolism and flavonoid biosynthesis pathways. The integrative analysis of transcriptomic, proteomic, biochemical and physiological data revealed that warming changed the expression of SpAMY, SpBGL, SpEGLC and SpAGPase genes, resulting in the reduction of NSCs and starch and the activation of sugar signaling, particularly SpSnRK1s, in female roots and male leaves. These sugar signals subsequently altered the expression of SpHCTs, SpLAR and SpDFR in the flavonoid biosynthetic pathway, ultimately leading to the differential accumulation of flavonoids in female and male S. paraplesia. Therefore, warming causes sexually differential responses of S. paraplesia, with females performing better than males.

Transcriptional Regulators of Plant Adaptation to Heat Stress

Heat stress (HS) is becoming an increasingly large problem for food security as global warming progresses. As sessile species, plants have evolved different mechanisms to cope with the disruption of cellular homeostasis, which can impede plant growth and development. Here, we summarize the mechanisms underlying transcriptional regulation mediated by transcription factors, epigenetic regulators, and regulatory RNAs in response to HS. Additionally, cellular activities for adaptation to HS are discussed, including maintenance of protein homeostasis through protein quality control machinery, and autophagy, as well as the regulation of ROS homeostasis via a ROS-scavenging system. Plant cells harmoniously regulate their activities to adapt to unfavorable environments. Lastly, we will discuss perspectives on future studies for improving urban agriculture by increasing crop resilience to HS.

Silicate solubilizing and plant growth promoting bacteria interact with biogenic silica to impart heat stress tolerance in rice by modulating physiology and gene expression

Heat stress caused due to increasing warming climate has become a severe threat to global food production including rice. Silicon plays a major role in improving growth and productivity of rice by aiding in alleviating heat stress in rice. Soil silicon is only sparingly available to the crops can be made available by silicate solubilizing and plant-growth-promoting bacteria that possess the capacity to solubilize insoluble silicates can increase the availability of soluble silicates in the soil. In addition, plant growth promoting bacteria are known to enhance the tolerance to abiotic stresses of plants, by affecting the biochemical and physiological characteristics of plants. The present study is intended to understand the role of beneficial bacteria viz. Rhizobium sp. IIRR N1 a silicate solublizer and Gluconacetobacter diazotrophicus, a plant growth promoting bacteria and their interaction with insoluble silicate sources on morpho-physiological and molecular attributes of rice (Oryza sativa L.) seedlings after exposure to heat stress in a controlled hydroponic system. Joint inoculation of silicates and both the bacteria increased silicon content in rice tissue, root and shoot biomass, significantly increased the antioxidant enzyme activities (viz. superoxidase dismutase, catalase and ascorbate peroxidase) compared to other treatments with sole application of either silicon or bacteria. The physiological traits (viz. chlorophyll content, relative water content) were also found to be significantly enhanced in presence of silicates and both the bacteria after exposure to heat stress conditions. Expression profiling of shoot and root tissues of rice seedlings revealed that seedlings grown in the presence of silicates and both the bacteria exhibited higher expression of heat shock proteins (HSPs viz., OsHsp90, OsHsp100 and 60 kDa chaperonin), hormone-related genes (OsIAA6) and silicon transporters (OsLsi1 and OsLsi2) as compared to seedlings treated with either silicates or with the bacteria alone. The results thus reveal the interactive effect of combined application of silicates along with bacteria Rhizobium sp. IIRR N1, G. diazotrophicus inoculation not only led to augmented silicon uptake by rice seedlings but also influenced the plant biomass and elicited higher expression of HSPs, hormone-related and silicon transporter genes leading to improved tolerance of seedling to heat stress.

Shifts in the diversity of root endophytic microorganisms across the life cycle of the ratooning rice Jiafuzhan

The diversity of root endophytic microorganisms, which is closely related to plant life activities, is known to vary with the plant growth stage. This study on the ratooning rice Jiafuzhan explored the diversity of the root endophytic bacteria and fungi and their dynamics during the plant life cycle. By sequencing the 16S ribosomal ribonucleic acid (16S rRNA) and internal transcribed spacer (ITS) genes, 12,154 operational taxonomic units (OTUs) and 497 amplicon sequence variants (ASVs) were obtained, respectively. The root endophytic microorganisms of rice in the seedling, tillering, jointing, heading, and mature stages of the first crop and at 13, 25, and 60 days after regeneration (at the heading, full heading, and mature stages of the second crop, respectively) were analyzed using diversity and correlation analyses. There were significant differences in the α-diversity and β-diversity of root endophytic bacteria and fungi in the growth stage. Additionally, linear discriminant analysis (LDA) effect size (LEfSe) analysis revealed biomarker bacteria for each growth stage, but biomarker fungi did not exist in every stage. Moreover, the correlation analysis showed that the bacterial and fungal biomarkers interacted with each other. Furthermore, the nitrogen-fixing genus Bradyrhizobium existed in all growth stages. These findings indicate the pattern of root endophytic microorganisms of ratooning rice at different growth stages, and they provide new insights into the high yield of the second crop of ratooning rice (in light of the abundance of various bacteria and fungi).

Enhancing heat stress tolerance in Lanzhou lily (Lilium davidii var. unicolor) with Trichokonins isolated from Trichoderma longibrachiatum SMF2

Lanzhou lily (Lilium davidii var. unicolor) is a renowned edible crop produced in China and relatively sensitive to high temperature (HT). Trichokonins (TKs) are antimicrobial peptaibols secreted from Trichoderma longibrachiatum strain SMF2. Here, we report that TKs application improves the thermotolerance of Lanzhou lily. The activity of the antioxidant enzyme system (SOD, CAT, and POD), the level of heat-resistance-associated phytohormones (ABA, SA, and JA), the relative water content (RWC), the content of chlorophyll (Chl), and the net photosynthetic rate (P _n) were promoted by TKs treatment in Lanzhou lily plants subjected to heat stress (HS). TKs treatment also mitigated cell injury as shown by a lower accumulation of malondialdehyde (MDA) and relative electrolyte leakage (REL) under HS conditions. RNA-seq data analysis showed that more than 4.5 times differentially expressed genes (DEGs) responded to TKs treatment under HS compared to non-HS, and TKs treatment reduced protein folding and enhanced cellular repair function under HS conditions. The analyses of DEGs involved in hormone (ABA, SA and JA) synthesis and signaling pathways suggested that TKs might improve Lanzhou lily heat tolerance by promoting ABA synthesis and signal transduction. TKs highly induced DEGs of the HSF-HSP pathway under HS, in which HSFA2 accounted for most of the HSF family. Furthermore, TKs treatment resulted in the upregulation of heat-protective genes LzDREB2B, LzHsfA2a, LzMBF1c, LzHsp90, and LzHsp70 involved in HSF-HSP signal pathway after long-term HS. LzHsfA2a-1 likely plays a key role in acquisition of TKs-induced thermotolerance of Lanzhou lily as evidenced by the sustained response to HS, the enhanced response to TKs treatment under long-term HS, and the high sequence similarity to LlHsfA2a which is a key regulator for the improvement of heat tolerance in Lilium longiflorum. Our results reveal the underlying mechanisms of TKs-mediated thermotolerance in Lanzhou lily and highlight an attractive approach to protecting crop plants from damage caused by HS in a global warming future.

Time-Series Transcriptomic Analysis of Contrasting Rice Materials under Heat Stress Reveals a Faster Response in the Tolerant Cultivar

Short-term heat stress can affect the growth of rice (Oryza sativa L.) seedlings, subsequently decreasing yields. Determining the dynamic response of rice seedlings to short-term heat stress is highly important for accelerating research on rice heat tolerance. Here, we observed the seedling characteristics of two contrasting cultivars (T11: heat-tolerant and T15: heat-sensitive) after different durations of 42 °C heat stress. The dynamic transcriptomic changes of the two cultivars were monitored after 0 min, 10 min, 30 min, 1 h, 4 h, and 10 h of stress. The results indicate that several pathways were rapidly responding to heat stress, such as protein processing in the endoplasmic reticulum, glycerophospholipid metabolism, and plant hormone signal transduction. Functional annotation and cluster analysis of differentially expressed genes at different stress times indicate that the tolerant cultivar responded more rapidly and intensively to heat stress compared to the sensitive cultivar. The MAPK signaling pathway was found to be the specific early-response pathway of the tolerant cultivar. Moreover, by combining data from a GWAS and RNA-seq analysis, we identified 27 candidate genes. The reliability of the transcriptome data was verified using RT-qPCR on 10 candidate genes and 20 genes with different expression patterns. This study provides valuable information for short-term thermotolerance response mechanisms active at the rice seedling stage and lays a foundation for breeding thermotolerant varieties via molecular breeding.

A non-specific lipid transfer protein, NtLTPI.38, positively mediates heat tolerance by regulating photosynthetic ability and antioxidant capacity in tobacco

Non-specific lipid transfer proteins (nsLTPs) play an important role in plant growth and stress resistance; however, their function in tobacco remains poorly understood. Therefore, to explore the function of NtLTP in response to high temperature, we identified an NtLTPI.38 from tobacco, obtained its overexpression and knockout transgenic plants, and further studied their response to heat stress (42 °C). The results showed that NtLTPI.38 overexpression in tobacco reduced chlorophyll degradation, alleviated the high temperature damage to photosynthetic organs, and enhanced the photosynthetic capacity of tobacco under heat stress. NtLTPI.38 overexpression in heat-stressed tobacco increased the contents of soluble sugar and protein, proline, and flavonoid substances, reduced the relative conductivity, and decreased H₂O₂, O₂^•-, and MDA accumulation, and increased the enzymatic antioxidant activities, such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX), compared to wild type (WT) and knockout mutant plants. RT-PCR confirmed that the expression levels of antioxidant enzymes and thermal stress-related genes were significantly upregulated under thermal stress in overexpression plants. Therefore, NtLTPI.38 enhanced heat tolerance in tobacco by mitigating photosynthetic damage and improving osmoregulation and antioxidant capacity. These results provided the theoretical basis and a potential resource for further breeding projects to improve heat tolerance in plants.

CRISPR-Cas9-based precise engineering of SlHyPRP1 protein towards multi-stress tolerance in tomato

Recently, CRISPR-Cas9-based genome editing has been widely used for plant breeding. In our previous report, a tomato gene encoding hybrid proline-rich protein 1 (HyPRP1), a negative regulator of salt stress responses, has been edited using a CRISPR-Cas9 multiplexing approach that resulted in precise eliminations of its functional domains, proline-rich domain (PRD) and eight cysteine-motif (8CM). We subsequently demonstrated that eliminating the PRD domain of HyPRP1 in tomatoes conferred the highest level of salinity tolerance. In this study, we characterized the edited lines under several abiotic and biotic stresses to examine the possibility of multiple stress tolerance. Our data reveal that the 8CM removal variants of HK and the KO alleles of both HK and 15T01 cultivars exhibited moderate heat stress tolerance. Similarly, plants carrying either the domains of the PRD removal variant (PR1v1) or 8CM removal variants (PR2v2 and PR2v3) showed better germination under osmosis stress (up to 200 mM mannitol) compared to the WT control. Moreover, the PR1v1 line continuously grew after 5 days of water cutoff. When the edited lines were challenged with pathogenic bacteria of Pseudomonas syringae pv. tomato (Pto) DC3000, the growth of the bacterium was significantly reduced by 2.0- to 2.5-fold compared to that in WT plants. However, the edited alleles enhanced susceptibility against Fusarium oxysporum f. sp. lycopersici, which causes fusarium wilt. CRISPR-Cas9-based precise domain editing of the SlHyPRP1 gene generated multi-stress-tolerant alleles that could be used as genetic materials for tomato breeding.

Nanobiotechnology in crop stress management: an overview of novel applications

Agricultural crops are subject to a variety of biotic and abiotic stresses that adversely affect growth and reduce the yield of crop plantss. Traditional crop stress management approaches are not capable of fulfilling the food demand of the human population which is projected to reach 10 billion by 2050. Nanobiotechnology is the application of nanotechnology in biological fields and has emerged as a sustainable approach to enhancing agricultural productivity by alleviating various plant stresses. This article reviews innovations in nanobiotechnology and its role in promoting plant growth and enhancing plant resistance/tolerance against biotic and abiotic stresses and the underlying mechanisms. Nanoparticles, synthesized through various approaches (physical, chemical and biological), induce plant resistance against these stresses by strengthening the physical barriers, improving plant photosynthesis and activating plant defense mechanisms. The nanoparticles can also upregulate the expression of stress-related genes by increasing anti-stress compounds and activating the expression of defense-related genes. The unique physico-chemical characteristics of nanoparticles enhance biochemical activity and effectiveness to cause diverse impacts on plants. Molecular mechanisms of nanobiotechnology-induced tolerance to abiotic and biotic stresses have also been highlighted. Further research is needed on efficient synthesis methods, optimization of nanoparticle dosages, application techniques and integration with other technologies, and a better understanding of their fate in agricultural systems.

Genome-Wide Identification and Expression Analysis of CCO Gene Family in Liriodendron chinense

Carotenoid cleavage oxygenase (CCO) is an enzyme that can catalyze carotenoids to volatile aromatic substances and participate in the biosynthesis of two important phytohormones, i.e., abscisic acid (ABA) and strigolactone (SL). However, the genome-wide identification and analysis of the CCO gene family in the rare and endangered woody plant Liriodendron chinense has not been reported. Here, we performed a genome-wide analysis of the CCO gene family in the L. chinense genome and examined its expression pattern during different developmental processes and in response to various abiotic stresses. A total of 10 LcCCO genes were identified and divided into 6 subfamilies according to the phylogenetic analysis. Subcellular localization prediction showed that most of the LcCCO proteins were located in the cytoplasm. Gene replication analysis showed that segmental and tandem duplication contributed to the expansion of this gene family in the L. chinense genome. Cis-element prediction showed that cis-elements related to plant hormones, stress and light response were widely distributed in the promoter regions of LcCCO genes. Gene expression profile analysis showed that LcNCED3b was extensively involved in somatic embryogenesis, especially the somatic embryo maturation, as well as in response to heat and cold stress in leaves. Furthermore, qRT-PCR analysis showed that LcNCED3b obviously responded to drought stress in roots and leaves. This study provides a comprehensive overview of the LcCCO gene family and a potential gene target for the optimization of the somatic embryogenesis system and resistance breeding in the valuable forest tree L. chinense.

Genome-wide characterization of RsHSP70 gene family reveals positive role of RsHSP70-20 gene in heat stress response in radish (Raphanus sativus L.)

Radish is an economical cool-season root vegetable crop worldwide. Heat shock protein 70 (HSP70) plays indispensable roles in plant growth, development and abiotic stress responses. Nevertheless, little information is available regarding the identification and functional characterization of HSP70 gene family in radish. Herein, a total of 34 RsHSP70 genes were identified at the radish genome level, among which nine and 25 RsHSP70s were classified into the HSP110/SSE and DnaK subfamilies, respectively. RNA-seq analysis revealed that some RsHSP70 genes had differential expression profile in radish leaf, root, stamen and pistil. A range of RsHSP70 genes exhibited differential expression under several abiotic stresses such as heat, salt and heavy metals. Intriguingly, the expression of four RsHSP70 genes (RsHSP70-7, RsHSP70-12, RsHSP70-20 and RsHSP70-22) was dramatically up-regulated under heat stress (HS). RT-qPCR and transient LUC reporter assay indicated that both the expression and promoter activity of RsHSP70-20 was strongly induced by HS. Notably, overexpression of RsHSP70-20 significantly enhanced thermotolerance by decreasing reactive oxygen species and promoting proline accumulation in radish, whereas its knock-down plants exhibited increased thermosensitivity, indicating that RsHSP70-20 positively regulate HS response in radish. These results would provide valuable information to decipher the molecular basis of RsHSP70-mediated thermotolerance in radish.

Ethylene: A Master Regulator of Plant-Microbe Interactions under Abiotic Stresses

The plant phytohormone ethylene regulates numerous physiological processes and contributes to plant-microbe interactions. Plants induce ethylene production to ward off pathogens after recognition of conserved microbe-associated molecular patterns (MAMPs). However, plant immune responses against pathogens are essentially not different from those triggered by neutral and beneficial microbes. Recent studies indicate that ethylene is an important factor for beneficial plant-microbial association under abiotic stress such as salt and heat stress. The association of beneficial microbes with plants under abiotic stresses modulates ethylene levels which control the expression of ethylene-responsive genes (ERF), and ERFs further regulate the plant transcriptome, epi-transcriptome, Na⁺/K⁺ homeostasis and antioxidant defense mechanisms against reactive oxygen species (ROS). Understanding ethylene-dependent plant-microbe interactions is crucial for the development of new strategies aimed at enhancing plant tolerance to harsh environmental conditions. In this review, we underline the importance of ethylene in beneficial plant-microbe interaction under abiotic stresses.

ERF49 mediates brassinosteroid regulation of heat stress tolerance in Arabidopsis thaliana

Background

Heat stress is a major abiotic stress affecting the growth and development of plants, including crop species. Plants have evolved various adaptive strategies to help them survive heat stress, including maintaining membrane stability, encoding heat shock proteins (HSPs) and ROS-scavenging enzymes, and inducing molecular chaperone signaling. Brassinosteroids (BRs) are phytohormones that regulate various aspects of plant development, which have been implicated also in plant responses to heat stress, and resistance to heat in Arabidopsis thaliana is enhanced by adding exogenous BR. Brassinazole resistant 1 (BZR1), a transcription factor and positive regulator of BR signal, controls plant growth and development by directly regulating downstream target genes. However, the molecular mechanism at the basis of BR-mediated heat stress response is poorly understood. Here, we report the identification of a new factor critical for BR-regulated heat stress tolerance.

Results

We identified ERF49 in a genetic screen for proteins required for BR-regulated gene expression. We found that ERF49 is the direct target gene of BZR1 and that overexpressing ERF49 enhanced sensitivity of transgenic plants to heat stress. The transcription levels of heat shock factor HSFA2, heat stress-inducible gene DREB2A, and three heat shock protein (HSP) were significantly reduced under heat stress in ERF49-overexpressed transgenic plants. Transcriptional activity analysis in protoplast revealed that BZR1 inhibits ERF49 expression by binding to the promoter of ERF49. Our genetic analysis showed that dominant gain-of-function brassinazole resistant 1-1D mutant (bzr1-1D) exhibited lower sensitivity to heat stress compared with wild-type. Expressing ERF49-SRDX (a dominant repressor reporter of ERF49) in bzr1-1D significantly decreased the sensitivity of ERF49-SRDX/bzr1-1D transgenic plants to heat stress compared to bzr1-1D.

Conclusions

Our data provide clear evidence that BR increases thermotolerance of plants by repressing the expression of ERF49 through BZR1, and this process is dependent on the expression of downstream heat stress-inducible genes. Taken together, our work reveals a novel molecular mechanism mediating plant response to high temperature stress.

Photosynthesis and chlorophyll fluorescence of Iranian licorice (Glycyrrhiza glabra l.) accessions under salinity stress

While salinity is increasingly becoming a prominent concern in arable farms around the globe, various treatments can be used for the mitigation of salt stress. Here, the effective presence of Azotobacter sp. inoculation (A₁) and absence of inoculation (A₀) was evaluated on Iranian licorice plants under NaCl stress (0 and 200 mM) (S₀ and S₁, respectively). In this regard, 16 Iranian licorice (Glycyrrhiza glabra L.) accessions were evaluated for the effects on photosynthesis and chlorophyll fluorescence. Leaf samples were measured for photosynthetic pigments (via a spectrophotometer), stomatal and trichome-related features (via SEM), along with several other morphological and biochemical features. The results revealed an increase in the amount of carotenoids that was caused by bacterial inoculation, which was 28.3% higher than the non-inoculated treatment. Maximum initial fluorescence intensity (F0) (86.7) was observed in the 'Bardsir' accession. Meanwhile, the highest variable fluorescence (Fv), maximal fluorescence intensity (Fm), and maximum quantum yield (Fv/Fm) (0.3, 0.4, and 0.8, respectively) were observed in the 'Eghlid' accession. Regarding anatomical observations of the leaf structure, salinity reduced stomatal density but increased trichome density. Under the effect of bacterial inoculation, salinity stress was mitigated. With the effect of bacterial inoculation under salinity stress, stomatal length and width increased, compared to the condition of no bacterial inoculation. Minimum malondialdehyde content was observed in 'Mahabad' accession (17.8 μmol/g _FW). Principle component analysis (PCA) showed that 'Kashmar', 'Sepidan', 'Bajgah', 'Kermanshah', and 'Taft' accessions were categorized in the same group while being characterized by better performance in the aerial parts of plants. Taken together, the present results generally indicated that selecting the best genotypes, along with exogenous applications of Azotobacter, can improve the outcomes of licorice cultivation for industrial purposes under harsh environments.

Changes and Correlation Between Physiological Characteristics of Rhododendron simsii and Soil Microbial Communities Under Heat Stress

The relationship between Rhododendron simsii and its soil microbial community under heat stress was not clear. In this study, the effects of heat stress on the physiological characteristics, soil physicochemical properties and soil microbial community structure of R. simsii were investigated. The experimental control (CK) was set as day/night (14/10 h) 25/20°C and experimental treatments were set as light heat stress (LHS) 35/30°C and high heat stress (HHS) 40/35°C. Our results showed that, compared with CK, LHS treatment significantly increased malondialdehyde, hydrogen peroxide, proline and soluble sugar contents, as well as catalase and peroxidase activities, while HHS treatment significantly increased ascorbate peroxidase activity and decreased chlorophyll content. Compared with CK, LHS treatment significantly reduced soil ammonium-nitrogen and nitrate-nitrogen content, while HHS significantly increased soil ammonium-nitrogen content. Compared with CK, both treatments changed the soil microbial community structure. For bacterial community, LHS and HHS treatment resulting in the significant enrichment of Burkholderia-Caballeronia-Paraburkholderia and Occallatibacte, respectively. For fungal community, LHS treatment resulting in the significant enrichment of Candida, Mortierella and Boothiomyces. The redundancy analysis showed that plant physiological characteristics, soil ammonium-nitrogen content were significantly correlated with the soil microbial community. Therefore, heat stress altered the soil microbial community structure, and affected the availability of soil available nitrogen, which in turn affected the physiological characteristics of R. simsii. We suggest that soil microbial community may play an important role in plant resistance to heat stress, and its mechanism deserves further study.

A Review on the Role of Endophytes and Plant Growth Promoting Rhizobacteria in Mitigating Heat Stress in Plants

Among abiotic stresses, heat stress is described as one of the major limiting factors of crop growth worldwide, as high temperatures elicit a series of physiological, molecular, and biochemical cascade events that ultimately result in reduced crop yield. There is growing interest among researchers in the use of beneficial microorganisms. Intricate and highly complex interactions between plants and microbes result in the alleviation of heat stress. Plant–microbe interactions are mediated by the production of phytohormones, siderophores, gene expression, osmolytes, and volatile compounds in plants. Their interaction improves antioxidant activity and accumulation of compatible osmolytes such as proline, glycine betaine, soluble sugar, and trehalose, and enriches the nutrient status of stressed plants. Therefore, this review aims to discuss the heat response of plants and to understand the mechanisms of microbe-mediated stress alleviation on a physio-molecular basis. This review indicates that microbes have a great potential to enhance the protection of plants from heat stress and enhance plant growth and yield. Owing to the metabolic diversity of microorganisms, they can be useful in mitigating heat stress in crop plants. In this regard, microorganisms do not present new threats to ecological systems. Overall, it is expected that continued research on microbe-mediated heat stress tolerance in plants will enable this technology to be used as an ecofriendly tool for sustainable agronomy.

PIF4 Promotes Expression of HSFA2 to Enhance Basal Thermotolerance in Arabidopsis

Heat stress (HS) seriously restricts the growth and development of plants. When plants are exposed to extreme high temperature, the heat stress response (HSR) is activated to enable plants to survive. Sessile plants have evolved multiple strategies to sense and cope with HS. Previous studies have established that PHYTOCHROME INTERACTING FACTOR 4 (PIF4) acts as a key component in thermomorphogenesis; however, whether PIF4 regulates plant thermotolerance and the molecular mechanism linking this light transcriptional factor and HSR remain unclear. Here, we show that the overexpression of PIF4 indeed provides plants with a stronger basal thermotolerance and greatly improves the survival ability of Arabidopsis under severe HS. Via phylogenetic analysis, we identified two sets (six) of PIF4 homologs in wheat, and the expression patterns of the PIF4 homologs were conservatively induced by heat treatment in both wheat and Arabidopsis. Furthermore, the PIF4 protein was accumulated under heat stress and had an identical expression level. Additionally, we found that the core regulator of HSR, HEAT SHOCK TRANSCRIPTION FACTOR A2 (HSFA2), was highly responsive to light and heat. Followed by promoter analysis and ChIP-qPCR, we further found that PIF4 can bind directly to the G-box motifs of the HSFA2 promoter. Via effector–reporter assays, we found that PIF4 binding could activate HSFA2 gene expression, thereby resulting in the activation of other HS-inducible genes, such as heat shock proteins. Finally, the overexpression of PIF4 led to a stronger basal thermotolerance under non-heat-treatment conditions, thereby resulting in an enhanced tolerance to severe heat stress. Taken together, our findings propose that PIF4 is linked to heat stress signaling by directly binding to the HSFA2 promoter and triggering the HSR at normal temperature conditions to promote the basal thermotolerance. These functions of PIF4 provide a candidate direction for breeding heat-resistant crop cultivars.

Redox status of the plant cell determines epigenetic modifications under abiotic stress conditions and during developmental processes

BACKGROUND

The oxidation-reduction (redox) status of the cell influences or regulates transcription factors and enzymes involved in epigenetic changes, such as DNA methylation, histone protein modifications, and chromatin structure and remodeling. These changes are crucial regulators of chromatin architecture, leading to differential gene expression in eukaryotes. But the cell's redox homeostasis is difficult to sustain since the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) is not equal in plants at different developmental stages and under abiotic stress conditions. Exceeding optimum ROS and RNS levels leads to oxidative stress and thus alters the redox status of the cell. Consequently, this alteration modulates intracellular epigenetic modifications that either mitigate or mediate the plant growth and stress response.

AIM OF REVIEW

Recent studies suggest that the altered redox status of the cell reform the cellular functions and epigenetic changes. Recent high-throughput techniques have also greatly advanced redox-mediated gene expression discovery, but the integrated view of the redox status, and its associations with epigenetic changes and subsequent gene expression in plants are still scarce. In this review, we accordingly focus on how the redox status of the cell affects epigenetic modifications in plants under abiotic stress conditions and during developmental processes. This is a first comprehensive review on the redox status of the cell covering the redox components and signaling, redox status alters the post-translational modification of proteins, intracellular epigenetic modifications, redox interplay during DNA methylation, redox regulation of histone acetylation and methylation, redox regulation of miRNA biogenesis, redox regulation of chromatin structure and remodeling and conclusion, future perspectives and biotechnological opportunities for the future development of the plants.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The interaction of redox mediators such as ROS, RNS and antioxidants regulates redox homeostasis and redox-mediated epigenetic changes. We discuss how redox mediators modulate epigenetic changes and show the opportunities for smart use of the redox status of the cell in plant development and abiotic stress adaptation. However, how a redox mediator triggers epigenetic modification without activating other redox mediators remains yet unknown.

Exogenous Rosmarinic Acid Application Enhances Thermotolerance in Tomatoes

Due to global warming, high-temperature stress has become a major threat to plant growth and development, which causes a severe challenge to food security worldwide. Therefore, it is necessary to explore the plant bioactive molecules, which could be a promising approach to strengthening plant thermotolerance. Rosmarinic acid (RA) serves as a plant-derived phenolic compound and has beneficial and health-promoting effects for human beings. However, the involvement of RA in plant stress response and the underlying molecular mechanism was largely unknown. In this study, we found that exogenous RA application conferred improved thermotolerance in tomatoes. The transcript abundance and the enzyme activity of enzymatic antioxidants, such as ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR), and dehydroascorbate reductase (DHAR), were further promoted by RA treatment in tomato plants subjected to high-temperature stress. Moreover, RA activated the antioxidant system and modulated the cellular redox homeostasis also associated with the redox status of nonenzymatic glutathione and ascorbic acid. The results of RNA-seq data showed that transcriptional regulation was involved in RA-mediated thermotolerance. Consistently, the gene expression of several high temperature-responsive transcription factors like HsfA2, and WRKY family genes were substantially induced by RA treatment, which potentially contributed to the induction of heat shock proteins (HSPs). Overall, these findings not only gave a direct link between RA and plant thermotolerance but also provided an attractive approach to protecting crop plants from high-temperature damage in a global warming future.