Microarray and genetic analysis reveals that csa-miR159b plays a critical role in abscisic acid-mediated heat tolerance in grafted cucumber plants

Deciphering miRNA-lncRNA-mRNA interaction through experimental validation of miRNAs, lncRNAs, and miRNA targets on mRNAs in Cajanus cajan

Pigeon pea (Cajanus cajan) is widely cultivated for its nutritional and medicinal value yet remains an orphan crop as productivity has not been improved because of a lack of genome and non-coding genome information. Non-coding RNAs, like miRNAs and long non-coding RNAs (lncRNAs), are involved in regulation of growth, metabolism, development, and stress response, and have a critical role in post-transcriptional gene regulation (PTGR). We attempted to elucidate the roles of miRNAs and lncRNAs in pigeon pea through experimental validation of computationally predicted miRNAs and lncRNAs and targets of miRNAs on mRNAs. We experimentally validated 20 miRNAs and 11 lncRNAs. We predicted cleavage sites of three miRNA targets: serine/threonine-protein kinase, polygalacturonase, beta-galactosidase. We identified 469 targets of 265 miRNAs and their functional annotations using computational methods. We built a miRNA-mRNA-lncRNA network model, with the miRNAs targeting both mRNAs and lncRNAs, to obtain information on the interplay of these three molecules. A confirmed interaction through experimental validation was established between miRNA, namely cca-miR1535a targeting the mRNA for beta-galactosidase, as well as the lncRNA cca-lnc-020033. Our findings increase knowledge of the non-coding genome of pigeon pea and their roles in PTGR and in improving agronomic traits of this pulse crop.

miRNAs and Their Target Genes Play a Critical Role in Response to Heat Stress in Cynodon dactylon (L.) Pers

Annual global temperature is increasing rapidly. Therefore, in the near future, plants will be exposed to severe heat stress. However, the potential of microRNAs-mediated molecular mechanism for modulating the expression of their target genes is unclear. To investigate the changes of miRNAs in thermo-tolerant plants, in this study, we first investigated the impact of four high temperature regimes including 35/30 °C, 40/35 °C, 45/40 °C, and 50/45 °C in a day/night cycle for 21 days on the physiological traits (total chlorophyll, relative water content and electrolyte leakage and total soluble protein), antioxidant enzymes activities (superoxide dismutase, ascorbic peroxidase, catalase and peroxidase), and osmolytes (total soluble carbohydrates and starch) in two bermudagrass accessions named Malayer and Gorgan. The results showed that more chlorophyll and the relative water content, lower ion leakage, more efficient protein and carbon metabolism and activation of defense proteins (such as antioxidant enzymes) in Gorgan accession, led to better maintained plant growth and activity during heat stress. In the next stage, to investigate the role of miRNAs and their target genes in response to heat stress in a thermo-tolerant plant, the impact of severe heat stress (45/40 °C) was evaluated on the expression of three miRNAs (miRNA159a, miRNA160a and miRNA164f) and their target genes (GAMYB, ARF17 and NAC1, respectively). All measurements were performed in leaves and roots simultaneously. Heat stress significantly induced the expression of three miRNAs in leaves of two accession, while having different effects on the expression of these miRNAs in roots. The results showed that a decrease in the expression of the transcription factor ARF17, no change in the expression of the transcription factor NAC1, and an increase in the expression of the transcription factor GAMYB in leaf and root tissues of Gorgan accession led to improved heat tolerance in it. These results also showed that the effect of miRNAs on the modulating expression of target mRNAs in leaves and roots is different under heat stress, and miRNAs and mRNAs show spatiotemporal expression. Therefore, the simultaneous analysis of miRNAs and mRNAs expressions in shoot and roots is needed to comprehensively understand miRNAs regulatory function under heat stress.

Impact of Climate Change on Regulation of Genes Involved in Sex Determination and Fruit Production in Cucumber

Environmental changes, both natural and anthropogenic, mainly related to rising temperatures and water scarcity, are clearly visible around the world. Climate change is important for crop production and is a major issue for the growth and productivity of cucumbers. Processes such as sex determination, flower morphogenesis and fruit development in cucumbers are highly sensitive to various forms of stress induced by climatic changes. It is noteworthy that many factors, including genetic factors, transcription factors, phytohormones and miRNAs, are crucial in regulating these processes and are themselves affected by climate change. Changes in the expression and activity of these factors have been observed as a consequence of climatic conditions. This review focuses primarily on exploring the effects of climate change and abiotic stresses, such as increasing temperature and drought, on the processes of sex determination, reproduction, and fruit development in cucumbers at the molecular level. In addition, it highlights the existing research gaps that need to be addressed in order to improve our understanding of the complex interactions between climate change and cucumber physiology. This, in turn, may lead to strategies to mitigate the adverse effects and enhance cucumber productivity in a changing climate.

Tomato SlMYB15 transcription factor targeted by sly-miR156e-3p positively regulates ABA-mediated cold tolerance

Cold is a common abiotic stress that seriously affects plant growth and development. MYB transcription factors are regulatory molecules that play important roles in various biological processes. We have previously demonstrated that SlMYB15 positively regulates cold tolerance in tomato. However, the underlying mechanism of SlMYB15-induced cold tolerance remains largely unexplored. Here, cold-induced SlMYB15 was found to be targeted by Solanum lycopersicum (sly)-miR156e-3p, which was decreased by cold stimulus in tomato. Tomato plants overexpressing sly-MIR156e-3p displayed significant enhancement in susceptibility to cold stress, while silencing of sly-miR156e-3p by an artificial microRNA interference strategy caused tomato plants to be more tolerant to cold. Moreover, both overexpression of SlMYB15 and silencing of sly-miR156e-3p increased the accumulation of ABA. SlMYB15 directly binds to the promoter regions of ABA biosynthesis and signalling genes, SlNCED1 and SlABF4, resulting in enhanced cold tolerance. Further experiments showed that SlMYB15 and sly-miR156e-3p also coordinated the cold tolerance of tomato via the reactive oxygen species (ROS) signalling pathway, as reflected by the increased expression of SlRBOH1, enhanced H2O2 and O2•-accumulation, and amplified activity of antioxidant enzymes in SlMYB15-overexpressing and sly-miR156e-3p-silenced plants. Taken together, our results demonstrate that SlMYB15 targeted by sly-miR156e-3p confers higher survivability to cold stress via ABA and ROS signals. This study provides valuable information for breeding improved crop cultivars better equipped with cold tolerance.

From single- to multi-omics: future research trends in medicinal plants

Medicinal plants are the main source of natural metabolites with specialised pharmacological activities and have been widely examined by plant researchers. Numerous omics studies of medicinal plants have been performed to identify molecular markers of species and functional genes controlling key biological traits, as well as to understand biosynthetic pathways of bioactive metabolites and the regulatory mechanisms of environmental responses. Omics technologies have been widely applied to medicinal plants, including as taxonomics, transcriptomics, metabolomics, proteomics, genomics, pangenomics, epigenomics and mutagenomics. However, because of the complex biological regulation network, single omics usually fail to explain the specific biological phenomena. In recent years, reports of integrated multi-omics studies of medicinal plants have increased. Until now, there have few assessments of recent developments and upcoming trends in omics studies of medicinal plants. We highlight recent developments in omics research of medicinal plants, summarise the typical bioinformatics resources available for analysing omics datasets, and discuss related future directions and challenges. This information facilitates further studies of medicinal plants, refinement of current approaches and leads to new ideas.

WRKY41/WRKY46-miR396b-5p-TPR module mediates abscisic acid-induced cold tolerance of grafted cucumber seedlings

Grafting is one of the key agronomic measures to enhance the tolerance to environmental stresses in horticultural plants, but the specific molecular regulation mechanism in this tolerance largely remains unclear. Here, we found that cucumber grafted onto figleaf gourd rootstock increased cold tolerance through abscisic acid (ABA) activating WRKY41/WRKY46-miR396b-5p-TPR (tetratricopeptide repeat-like superfamily protein) module. Cucumber seedlings grafted onto figleaf gourd increased cold tolerance and induced the expression of miR396b-5p. Furthermore, overexpression of cucumber miR396b-5p in Arabidopsis improved cold tolerance. 5' RNA ligase-mediated rapid amplification of cDNA ends (5' RLM-RACE) and transient transformation experiments demonstrated that TPR was the target gene of miR396b-5p, while TPR overexpression plants were hypersensitive to cold stress. The yeast one-hybrid and dual-luciferase assays showed that both WRKY41 and WRKY46 bound to MIR396b-5p promoter to induce its expression. Furthermore, cold stress enhanced the content of ABA in the roots and leaves of figleaf gourd grafted cucumber seedlings. Exogenous application of ABA induced the expression of WRKY41 and WRKY46, and cold tolerance of grafted cucumber seedlings. However, figleaf gourd rootstock-induced cold tolerance was compromised when plants were pretreated with ABA biosynthesis inhibitor. Thus, ABA mediated figleaf gourd grafting-induced cold tolerance of cucumber seedlings through activating the WRKY41/WRKY46-miR396b-5p-TPR module.

New insights into pathogen-mediated modulation of host RNA splicing

Alternative splicing (AS) regulation of pre-mRNA has been proven to be one of the fundamental layers of plant immune system. How pathogens disrupt plant AS process to suppress plant immunity by secreted effectors remain poorly understood. In the recent study, Gui et al. revealed that a previously identified effector PSR1 of Phytophthora interferes with host RNA splicing machinery to modulate small RNA biogenesis, leading to compromised plant immunity. The study provided a novel insight into the importance of AS process during pathogen-host interactions.

Engineering drought-tolerant apple by knocking down six GH3 genes and potential application of transgenic apple as a rootstock

Drought poses a major threat to apple fruit production and quality. Because of the apple's long juvenile phase, developing varieties with improved drought tolerance using biotechnology approaches is needed. Here, we used the RNAi approach to knock down six GH3 genes in the apple. Under prolonged drought stress, the MdGH3 RNAi plants performed better than wild-type plants and had stronger root systems, higher root-to-shoot ratio, greater hydraulic conductivity, increased photosynthetic capacity, and increased water use efficiency. Moreover, MdGH3 RNAi plants promoted the drought tolerance of the scion when they were used as rootstock, compared with wild-type and M9-T337 rootstocks. Scions grafted onto MdGH3 RNAi plants showed increased plant height, stem diameter, photosynthetic capacity, specific leaf weight, and water use efficiency. The use of MdGH3 RNAi plants as rootstocks can also increase the C/N ratio of the scion and achieve the same effect as the M9-T337 rootstock in promoting the flowering and fruiting of the scion. Notably, using MdGH3 RNAi plants as rootstocks did not reduce fruit weight and scion quality compared with using M9-T337 rootstock. Our research provides candidate genes and demonstrates a general approach that could be used to improve the drought tolerance of fruit trees without sacrificing the yield and quality of scion fruits.

CsbZIP2-miR9748-CsNPF4.4 Module Mediates High Temperature Tolerance of Cucumber Through Jasmonic Acid Pathway

High temperature stress seriously affects the growth of cucumber seedlings, and even leads to a decline in yield and quality. miRNAs have been shown to be involved in regulating the response to stress in plants, but little is known about its effects on cucumber high temperature stress tolerance. Here, we found that high temperature stress induced the expression of miR9748 in cucumber. Overexpression of cucumber miR9748 in Arabidopsis improved high temperature tolerance. Transcriptome analysis revealed that miR9748 might mediate high temperature tolerance through plant hormone signal pathway. 5' RNA ligase-mediated rapid amplification of cDNA ends (5' RLM-RACE) and transient transformation technology demonstrated that CsNPF4.4 was the target gene of miR9748. CsNPF4.4 overexpression plants decreased high temperature tolerance accompanied by reducing the content of jasmonic acid (JA), but alleviated by foliar application of methyl jasmonate, indicating that CsNPF4.4 negatively regulated high temperature stress tolerance through inhibition JA signal pathway. Furthermore, high temperature stress also increased the expression level of CsbZIP2. Yeast one-hybrid and dual-luciferase assays showed that CsbZIP2 directly bound to the promoter of MIR9748 to induce its expression. Taken together, our results indicated that CsbZIP2 directly regulated miR9748 expression to cleave CsNPF4.4 to mediate high temperature tolerance through JA pathway.

Uncovering the Epigenetic Marks Involved in Mediating Salt Stress Tolerance in Plants

The toxic effects of salinity on agricultural productivity necessitate development of salt stress tolerance in food crops in order to meet the escalating demands. Plants use sophisticated epigenetic systems to fine-tune their responses to environmental cues. Epigenetics is the study of heritable, covalent modifications of DNA and histone proteins that regulate gene expression without altering the underlying nucleotide sequence and consequently modify the phenotype. Epigenetic processes such as covalent changes in DNA, histone modification, histone variants, and certain non-coding RNAs (ncRNA) influence chromatin architecture to regulate its accessibility to the transcriptional machinery. Under salt stress conditions, there is a high frequency of hypermethylation at promoter located CpG sites. Salt stress results in the accumulation of active histones marks like H3K9K14Ac and H3K4me3 and the downfall of repressive histone marks such as H3K9me2 and H3K27me3 on salt-tolerance genes. Similarly, the H2A.Z variant of H2A histone is reported to be down regulated under salt stress conditions. A thorough understanding of the plasticity provided by epigenetic regulation enables a modern approach to genetic modification of salt-resistant cultivars. In this review, we summarize recent developments in understanding the epigenetic mechanisms, particularly those that may play a governing role in the designing of climate smart crops in response to salt stress.

Emerging Strategies Mold Plasticity of Vegetable Plants in Response to High Temperature Stress

As a result of energy consumption and human activities, a large amount of carbon dioxide emissions has led to global warming, which seriously affects the growth and development of plants. Vegetables are an indispensable part of people's diet. In the plant kingdom, a variety of vegetables are highly sensitive to climate change. For them, an increase of just a few degrees above their optimum temperature threshold can result in a loss of yield and quality. Emerging strategies such as practice management and breeding varieties in response to above-optimal temperatures are critical for abiotic stress resistance of vegetable crops. In this study, the function and application of multiple strategies, including breeding improvement, epigenetic modification directed generation of alleles, gene editing techniques, and accumulation of mutations in multigenerational adaptation to abiotic stress, were discussed in vegetable crops. It is believed to be meaningful for plants to build plasticity under high temperature stress, thus generating more genetic structures for heat resistant traits in vegetable products.

Regulation of small RNA-mediated high temperature stress responses in crop plants

Small RNAs have emerged as key players of gene expression regulation. Several lines of evidences highlight their role in modulating high temperature stress responsiveness in plants. Throughout their life cycle, plants have to regulate their gene expression at various developmental phases, physiological changes, and in response to biotic or environmental stress. High temperature is one the most common abiotic stress for crop plants, that results in impaired morphology, physiology, and yield. However, plants have certain mechanisms that enable them to withstand such conditions by modulating the expression of stress-related genes. Small RNA (sRNA)-regulated gene expression is one such mechanism which is ubiquitous in all eukaryotes. The sRNAs mainly include micro RNAs (miRNAs) and small interfering RNAs (siRNAs). They are primarily associated with the gene silencing either through translation inhibition, mRNA degradation, or DNA methylation. During high temperature stress the increased or decreased level of miRNAs altered the protein accumulation of target transcripts and, therefore, regulate stress responses. Several reports are available in plants which are genetically engineered through expressing artificial miRNAs resulted in thermotolerance. sRNAs have also been reported to bring the epigenetic changes on chromatin region through RNA-dependent DNA methylation (RdDM). The present article draws a brief illustration of sRNA origin, their functional mechanisms, role in high temperature stress, and possible application for developing stress tolerant crop plants.

Long-distance control of pumpkin rootstock over cucumber scion under drought stress as revealed by transcriptome sequencing and mobile mRNAs identifications

Grafting with pumpkin rootstock is commonly used not only to improve the quality of cucumber fruits but also to confer biotic or abiotic stress tolerance. However, the molecular mechanism of grafted cucumbers to drought stress and the possible roles of mobile mRNAs to improve stress tolerance have remained obscure. Hence, we conducted transcriptome sequencing and combined it with morpho-physiological experiments to compare the response of homografts (cucumber as scion and rootstock) (C) and heterografts (cucumber as scion and pumpkin as rootstock) (P) to drought stress. After applying drought stress, homografts and heterografts expressed 2960 and 3088 genes in response to drought stress, respectively. The identified DEGs in heterografts under drought stress were categorized into different stress-responsive groups, such as carbohydrate metabolism (involved in osmotic adjustment by sugar accumulation), lipid and cell wall metabolism (involved in cell membrane integrity by a reduction in lipid peroxidation), redox homeostasis (increased antioxidant enzymes activities), phytohormone (increased ABA content), protein kinases and transcription factors (TFs) using MapMan software. Earlier and greater H2O2 accumulation in xylem below the graft union was accompanied by leaf ABA accumulation in heterografts in response to drought stress. Greater leaf ABA helped heterografted cucumbers to sense and respond to drought stress earlier than homografts. The timely response of heterografts to drought stress led to maintain higher water content in the leaves even in the late stage of drought stress. The identified mobile mRNAs (mb-mRNAs) in heterografts were mostly related to photosynthesis which would be the possible reason for improved chlorophyll content and maximum photochemical efficiency of PSII (Fv/Fm). The existence of some stress-responsive pumpkin (rootstock) mRNAs in cucumber (scion), such as heat shock protein (HSP70, a well-known stress-responsive gene), led to the higher proline accumulation than homografts. The expression of the mobile and immobile stress-responsive mRNAs and timely response of heterografts to drought stress could improve drought tolerance in pumpkin-rooted plants.

Abscisic Acid Mediates Grafting-Induced Cold Tolerance of Watermelon via Interaction With Melatonin and Methyl Jasmonate

Grafting is widely used to increase plant defense responses to various stresses. Grafting-induced cold tolerance is associated with the increase of the antioxidant potential of plants; however, the underlying mechanisms remain unclear. Here, we found that pumpkin rootstocks promote antioxidant enzyme activities and alleviate cold-induced oxidative damage, accompanied by increased abscisic acid (ABA), melatonin, and methyl jasmonate (MeJA) levels in leaves. Increased ABA accumulation in leaves was attributed partly to the increased ABA levels in rootstocks. ABA induced antioxidant enzymes activities and the accumulation of melatonin and MeJA, while inhibition of ABA synthesis blocked the rootstock-induced antioxidant activity and the accumulation of melatonin and MeJA under cold stress. Melatonin and MeJA application also enhanced ABA accumulation in leaves after cold exposure, whereas inhibition of melatonin or MeJA synthesis attenuated the rootstock-induced increase of ABA. Moreover, melatonin and MeJA application alleviated cold-induced oxidative stress, but inhibition of melatonin or MeJA synthesis lowered the rootstock- or ABA-induced antioxidant potential and tolerance to cold. These findings indicate that ABA plays an important role in the grafting-induced cold tolerance by promoting the accumulation of melatonin and MeJA, which in turn, promote ABA accumulation, forming a positive feedback loop.

Soybean miR159-GmMYB33 Regulatory Network Involved in Gibberellin-Modulated Resistance to Heterodera glycines

Soybean cyst nematode (SCN, Heterodera glycines) is an obligate sedentary biotroph that poses major threats to soybean production globally. Recently, multiple miRNAome studies revealed that miRNAs participate in complicated soybean-SCN interactions by regulating their target genes. However, the functional roles of miRNA and target genes regulatory network are still poorly understood. In present study, we firstly investigated the expression patterns of miR159 and targeted GmMYB33 genes. The results showed miR159-3p downregulation during SCN infection; conversely, GmMYB33 genes upregulated. Furthermore, miR159 overexpressing and silencing soybean hairy roots exhibited strong resistance and susceptibility to H. glycines, respectively. In particular, miR159-GAMYB genes are reported to be involve in GA signaling and metabolism. Therefore, we then investigated the effects of GA application on the expression of miR159-GAMYB module and the development of H. glycines. We found that GA directly controls the miR159-GAMYB module, and exogenous GA application enhanced endogenous biologically active GA1 and GA3, the abundance of miR159, lowered the expression of GmMYB33 genes and delayed the development of H. glycines. Moreover, SCN infection also results in endogenous GA content decreased in soybean roots. In summary, the soybean miR159-GmMYB33 module was directly involved in the GA-modulated soybean resistance to H. glycines.

The Novel Cucurbitaceae miRNA ClmiR86 Is Involved in Grafting-Enhanced Phosphate Utilization and Phosphate Starvation Tolerance in Watermelon

Watermelon (Citrullus lanatus) is a globally important Cucurbitaceae crop in which grafting is commonly used to improve stress tolerance and enhance nutrient utilization. However, the mechanism underlying grafting-enhanced nutrient assimilation remains unclear. Here, we demonstrate the possible involvement of a novel Cucurbitaceae miRNA, ClmiR86, in grafting-enhanced phosphate-starvation tolerance via CALCINEURIN B-LIKE INTERACTING PROTEIN KINASE 5 (ClCIPK5) suppression in watermelon. Transcript analyses revealed that the induction of ClmiR86 expression was correlated with the downregulation of ClCIPK5 in squash-grafted watermelon under phosphate starvation. In addition, the differential expression of ClmiR86 in various watermelon genotypes was consistent with their phosphate utilization efficiency. Furthermore, ClmiR86 overexpression in Arabidopsis enhanced root growth and phosphate uptake under phosphate starvation and promoted inflorescence elongation under normal conditions. These results suggest that the ClmiR86–ClCIPK5 axis is involved in phosphate starvation response as well as grafting-enhanced growth vigor and phosphate assimilation. The present study provides valuable insights for investigating long-distance signaling and nutrient utilization in plants.

Small RNAs: The Essential Regulators in Plant Thermotolerance

Small RNAs (sRNAs) are a class of non-coding RNAs that consist of 21-24 nucleotides. They have been extensively investigated as critical regulators in a variety of biological processes in plants. sRNAs include two major classes: microRNAs (miRNAs) and small interfering RNAs (siRNAs), which differ in their biogenesis and functional pathways. Due to global warming, high-temperature stress has become one of the primary causes for crop loss worldwide. Recent studies have shown that sRNAs are involved in heat stress responses in plants and play essential roles in high-temperature acclimation. Genome-wide studies for heat-responsive sRNAs have been conducted in many plant species using high-throughput sequencing. The roles for these sRNAs in heat stress response were also unraveled subsequently in model plants and crops. Exploring how sRNAs regulate gene expression and their regulatory mechanisms will broaden our understanding of sRNAs in thermal stress responses of plant. Here, we highlight the roles of currently known miRNAs and siRNAs in heat stress responses and acclimation of plants. We also discuss the regulatory mechanisms of sRNAs and their targets that are responsive to heat stress, which will provide powerful molecular biological resources for engineering crops with improved thermotolerance.

Genome-wide prediction of cauliflower miRNAs and lncRNAs and their roles in post-transcriptional gene regulation

We have predicted miRNAs, their targets and lncRNAs from the genome of Brassica oleracea along with their functional annotation. Selected miRNAs and their targets are experimentally validated. Roles of these non-coding RNAs in post-transcriptional gene regulation are also deciphered. Cauliflower (Brassica oleracea var. Botrytis) is an important vegetable crop for its dietary and medicinal values with rich source of vitamins, dietary fibers, flavonoids and antioxidants. MicroRNAs (miRNAs) are small non-coding RNAs (ncRNAs), which regulate gene expression by inhibiting translation or by degrading messenger RNAs (mRNAs). On the other hand, long non-coding RNAs (lncRNAs) are responsible for the up regulation and the down regulation of transcription. Although the genome of cauliflower is reported, yet the roles of these ncRNAs in post-transcriptional gene regulation (PTGR) remain elusive. In this study, we have computationally predicted 355 miRNAs, of which 280 miRNAs are novel compared to miRBase 22.1. All the predicted miRNAs belong to 121 different families. We have also identified 934 targets of 125 miRNAs along with their functional annotation. These targets are further classified into biological processes, molecular functions and cellular components. Moreover, we have predicted 634 lncRNAs, of which 61 are targeted by 30 novel miRNAs. Randomly chosen 10 miRNAs and 10 lncRNAs are experimentally validated. Five miRNA targets including squamosa promoter-binding-like protein 9, homeobox-leucine zipper protein HDG12-like, NAC domain-containing protein 100, CUP-SHAPED COTYLEDON 1 and kinesin-like protein NACK2 of four miRNAs including bol-miR156a, bol-miR162a, bol-miR164d and bol-miR2673 are also experimentally validated. We have built network models of interactions between miRNAs and their target mRNAs, as well as between miRNAs and lncRNAs. Our findings enhance the knowledge of non-coding genome of cauliflower and their roles in PTGR, and might play important roles in improving agronomic traits of this economically important crop.

Identification and characterization of heat-responsive microRNAs at the booting stage in two rice varieties, 9311 and Nagina 22

MicroRNAs (miRNAs) are small, non-coding, regulatory RNAs that play important roles in abiotic stress responses in plants, but their regulatory roles in the adaptive response to heat stress at the booting stage in two rice varieties, 9311 and Nagina 22, remain largely unknown. In this study, 464 known miRNAs and 123 potential novel miRNAs were identified. Of these miRNAs, a total of 90 differentially expressed miRNAs were obtained with 9311 libraries as the control group, of which 54 were upregulated and 36 were downregulated. To gain insight into functional significance, 2773 potential target genes of these 90 differentially expressed miRNAs were predicted. GO enrichment analysis showed that the predicted target genes of differentially expressed miRNAs included NACs, LACs, CSD, and Hsp40. KEGG pathway analysis showed that the target genes of these differentially expressed miRNAs were significantly enriched in the plant hormone signal transduction pathway. The expression levels of 10 differentially expressed miRNAs and their target genes obtained by qRT-PCR were largely consistent with the sequencing results. This study lays a foundation for the elucidation of the miRNA-mediated regulatory mechanisms in rice at elevated temperatures.

The calcium-dependent protein kinase ZmCDPK7 functions in heat-stress tolerance in maize

Global warming poses a serious threat to crops. Calcium-dependent protein kinases (CDPKs)/CPKs play vital roles in plant stress responses, but their exact roles in plant thermotolerance remains elusive. Here, we explored the roles of heat-induced ZmCDPK7 in thermotolerance in maize. ZmCDPK7-overexpressing maize plants displayed higher thermotolerance, photosynthetic rates, and antioxidant enzyme activity but lower H₂ O₂ and malondialdehyde (MDA) contents than wild-type plants under heat stress. ZmCDPK7-knockdown plants displayed the opposite patterns. ZmCDPK7 is attached to the plasma membrane but can translocate to the cytosol under heat stress. ZmCDPK7 interacts with the small heat shock protein sHSP17.4, phosphorylates sHSP17.4 at Ser-44 and the respiratory burst oxidase homolog RBOHB at Ser-99, and upregulates their expression. Site-directed mutagenesis of sHSP17.4 to generate a Ser-44-Ala substitution reduced ZmCDPK7's enhancement of catalase activity but enhanced ZmCDPK7's suppression of MDA accumulation in heat-stressed maize protoplasts. sHSP17.4, ZmCDPK7, and RBOHB were less strongly upregulated in response to heat stress in the abscisic acid-deficient mutant vp5 versus the wild type. Pretreatment with an RBOH inhibitor suppressed sHSP17.4 and ZmCDPK7 expression. Therefore, abscisic acid-induced ZmCDPK7 functions both upstream and downstream of RBOH and participates in thermotolerance in maize by mediating the phosphorylation of sHSP17.4, which might be essential for its chaperone function.

GC-MS analysis combined with sensory analysis revealed the various aroma characteristics of black tea resulted from different grafting rootstocks

The study was aim to investigate the effects of grafting on volatile compounds and sensory quality of black tea. Seven groups of black tea were prepared from one nongrafted tea tree "Yinghong9 (YJ)" and six grafted tea trees by grafting scion of "YingHong9" on different rootstocks. Sensory analysis indicated marked/slight variations among seven samples, among which, the one grafting on HuangZhiXiangDanCong (HZX) stood out with floral and fruity aroma. The result of chemometrics analysis suggested various effects on compounds caused by different rootstocks. A total of 38 differential compounds were identified, showing mainly quantitative variations, with 36 being identified in all samples. The significant higher contents of volatiles, such as geraniol, phenylethyl alcohol, (E)-nerolidol, decanal, and linalool oxides, in HZX compared with YJ were observed, which explained why floral and fruity aroma stood out among the whole aroma profile of HZX. Both results of sensory and instrumental analysis suggested certain correlation between compound variations and aroma characteristics. Moreover, different rootstocks influenced the aroma quality in different ways. PRACTICAL APPLICATION: In conclusion, the study illuminates the various effects of grafting on the volatile compounds and aroma quality, which enlightens the possibility of changing aroma quality of black tea by grafting scions on different rootstocks. And thus, it can help guide the practical production when cultivating new varieties.

A new adenylyl cyclase, putative disease-resistance RPP13-like protein 3, participates in abscisic acid-mediated resistance to heat stress in maize

In plants, 3´,5´-cyclic adenosine monophosphate (cAMP) is an important second messenger with varied functions; however, only a few adenylyl cyclases (ACs) that synthesize cAMP have been identified. Moreover, the biological roles of ACs/cAMP in response to stress remain largely unclear. In this study, we used quantitative proteomics techniques to identify a maize heat-induced putative disease-resistance RPP13-like protein 3 (ZmRPP13-LK3), which has three conserved catalytic AC centres. The AC activity of ZmRPP13-LK3 was confirmed by in vitro enzyme activity analysis, in vivo RNAi experiments, and functional complementation in the E. coli cyaA mutant. ZmRPP13-LK3 is located in the mitochondria. The results of in vitro and in vivo experiments indicated that ZmRPP13-LK3 interacts with ZmABC2, a possible cAMP exporter. Under heat stress, the concentrations of ZmRPP13-LK3 and cAMP in the ABA-deficient mutant vp5 were significantly less than those in the wild-type, and treatment with ABA and an ABA inhibitor affected ZmRPP13-LK3 expression in the wild-type. Application of 8-Br-cAMP, a cAMP analogue, increased heat-induced expression of heat-shock proteins in wild-type plants and alleviated heat-activated oxidative stress. Taken together, our results indicate that ZmRPP13-LK3, a new AC, can catalyse ATP for the production of cAMP and may be involved in ABA-regulated heat resistance.

Comparative Analysis of Transcriptome and sRNAs Expression Patterns in the Brachypodium distachyon- Magnaporthe oryzae Pathosystems

The hemibiotrophic fungus Magnaporthe oryzae (Mo) is the causative agent of rice blast and can infect aerial and root tissues of a variety of Poaceae, including the model Brachypodium distachyon (Bd). To gain insight in gene regulation processes occurring at early disease stages, we comparatively analyzed fungal and plant mRNA and sRNA expression in leaves and roots. A total of 310 Mo genes were detected consistently and differentially expressed in both leaves and roots. Contrary to Mo, only minor overlaps were observed in plant differentially expressed genes (DEGs), with 233 Bd-DEGs in infected leaves at 2 days post inoculation (DPI), compared to 4978 at 4 DPI, and 138 in infected roots. sRNA sequencing revealed a broad spectrum of Mo-sRNAs that accumulated in infected tissues, including candidates predicted to target Bd mRNAs. Conversely, we identified a subset of potential Bd-sRNAs directed against fungal cell wall components, virulence genes and transcription factors. We also show a requirement of operable RNAi genes from the DICER-like (DCL) and ARGONAUTE (AGO) families for fungal virulence. Overall, our work elucidates the extensive reprogramming of transcriptomes and sRNAs in both plant host (Bd) and fungal pathogen (Mo), further corroborating the critical role played by sRNA species in the establishment of the interaction and its outcome.

Genome-Wide Comparative Analysis of R2R3 MYB Gene Family in Populus and Salix and Identification of Male Flower Bud Development-Related Genes

The MYB transcription factor (TF) family is one of the largest plant transcription factor gene family playing vital roles in plant growth and development, including defense, cell differentiation, secondary metabolism, and responses to biotic and abiotic stresses. As a model tree species of woody plants, in recent years, the identification and functional prediction of certain MYB family members in the poplar genome have been reported. However, to date, the characterization of the gene family in the genome of the poplar's sister species willow has not been done, nor are the differences and similarities between the poplar and willow genomes understood. In this study, we conducted the first genome-wide investigation of the R2R3 MYB subfamily in the willow, identifying 216 R2R3 MYB gene members, and combined with the poplar R2R3 MYB genes, performed the first comparative analysis of R2R3 MYB genes between the poplar and willow. We identified 81 and 86 pairs of R2R3 MYB paralogs in the poplar and willow, respectively. There were 17 pairs of tandem repeat genes in the willow, indicating active duplication of willow R2R3 MYB genes. A further 166 pairs of poplar and willow orthologs were identified by collinear and synonymous analysis. The findings support the duplication of R2R3 MYB genes in the ancestral species, with most of the R2R3 MYB genes being retained during the evolutionary process. The phylogenetic trees of the R2R3 MYB genes of 10 different species were drawn. The functions of the poplar and willow R2R3 MYB genes were predicted using reported functional groupings and clustering by OrthoFinder. Identified 5 subgroups in general expanded in woody species, three subgroups were predicted to be related to lignin synthesis, and we further speculate that the other two subgroups also play a role in wood formation. We analyzed the expression patterns of the GAMYB gene of subgroup 18 (S18) related to pollen development in the male flower buds of poplar and willow at different developmental stages by qRT-PCR. The results showed that the GAMYB gene was specifically expressed in the male flower bud from pollen formation to maturity, and that the expression first increased and then decreased. Both the specificity of tissue expression specificity and conservation indicated that GAMYB played an important role in pollen development in both poplar and willow and was an ideal candidate gene for the analysis of male flower development-related functions of the two species.

Phenotypic Characteristics and Transcriptome of Cucumber Male Flower Development Under Heat Stress

Cucumber (Cucumis sativus L.) is an important vegetable crop, which is thermophilic not heat resistant. High-temperature stress always results in sterility at reproductive stage. In the present study, we evaluate the male flower developmental changes under normal (CK) and heat stress (HS) condition. After HS, the activities of peroxidase (POD) and superoxide dismutase (SOD) and the contents of malondialdehyde (MDA) were increased. In addition, the pollen fertility was significantly decreased; and abnormal tapetum and microspore were observed by paraffin section. Transcriptome analysis results presented that total of 5828 differentially expressed genes (DEGs) were identified after HS. Among these DEGs, 20 DEGs were found at four stages, including DNA binding transcription factor, glycosyltransferase, and wound-responsive family protein. The gene ontology term of carbohydrate metabolic process was significantly enriched in all anther stages, and many saccharides and starch synthase-related genes, such as invertase, sucrose synthase, and starch branching enzyme, were significantly different expressed in HS compared with CK. Furthermore, co-expression network analysis showed a module (midnightblue) strongly consistent with HS, and two hub genes (CsaV3_6G004180 and CsaV3_5G034860) were found with a high degree of connectivity to other genes. Our results provide comprehensive understandings on male flower development in cucumber under HS.

The Impact of Zinc Oxide Nanoparticles on Cytotoxicity, Genotoxicity, and miRNA Expression in Barley (Hordeum vulgare L.) Seedlings

Zinc oxide nanoparticles are one of the most commonly engineered nanomaterials and necessarily enter the environment because of the large quantities produced and their widespread application. Understanding the impacts of nanoparticles on plant growth and development is crucial for the assessment of probable environmental risks to food safety and human health, because plants are a fundamental living component of the ecosystem and the most important source in the human food chain. The objective of this study was to examine the impact of different concentrations of zinc oxide nanoparticles on barley Hordeum vulgare L. seed germination, seedling morphology, root cell viability, stress level, genotoxicity, and expression of miRNAs. The results demonstrate that zinc oxide nanoparticles enhance barley seed germination, shoot/root elongation, and H₂O₂ stress level and decrease root cell viability and genomic template stability and up- and downregulated miRNAs in barley seedlings.

The lre-miR159a-LrGAMYB pathway mediates resistance to grey mould infection in Lilium regale

Grey mould is one of the most determinative factors of lily growth and plays a major role in limiting lily productivity. MicroRNA159 (miR159) is a highly conserved microRNA in plants, and participates in the regulation of plant development and stress responses. Our previous studies revealed that lre-miR159a participates in the response of Lilium regale to Botrytis elliptica according to deep sequencing analyses; however, the response mechanism remains unknown. Here, lre-miR159a and its target LrGAMYB gene were isolated from L. regale. Transgenic Arabidopsis overexpressing lre-MIR159a exhibited larger leaves and smaller necrotic spots on inoculation with Botrytis than those of wild-type and overexpressing LrGAMYB plants. The lre-MIR159a overexpression also led to repressed expression of two targets of miR159, AtMYB33 and AtMYB65, and enhanced accumulation of hormone-related genes, including AtPR1, AtPR2, AtNPR1, AtPDF1.2, and AtLOX for both the jasmonic acid and salicylic acid pathways. Moreover, lower levels of H₂ O₂ and O2- were observed in lre-MIR159a transgenic Arabidopsis, which reduced the damage from reactive oxygen species accumulation. Taken together, these results indicate that lre-miR159a positively regulates resistance to grey mould by repressing the expression of its target LrGAMYB gene and activating a defence response.

Bitter Melon (Momordica charantia L.) Rootstock Improves the Heat Tolerance of Cucumber by Regulating Photosynthetic and Antioxidant Defense Pathways

High temperature is considered a critical abiotic stressor that is increasing continuously, which is severely affecting plant growth and development. The use of heat-resistant rootstock grafting is a viable technique that is practiced globally to improve plant resistance towards abiotic stresses. In this experiment, we explored the efficacy of bitter melon rootstock and how it regulates photosynthesis and the antioxidant defense system to alleviate heat stress (42 °C/32 °C) in cucumber. Our results revealed that bitter-melon-grafted seedlings significantly relieved heat-induced growth inhibition and photoinhibition, maintained better photosynthesis activity, and accumulated a greater biomass than self-grafted seedlings. We measured the endogenous polyamine and hydrogen peroxide (H2O2) contents to determine the inherent mechanism responsible for these effects, and the results showed that heat stress induced a transient increase in polyamines and H2O2 in the inner courtyard of grafted seedlings. This increment was greater and more robust in bitter-melon-grafted seedlings. In addition, the use of polyamine synthesis inhibitors MGBG (methylglyoxal bis-guanylhydrazone) and D-Arg (D-arginine), further confirmed that the production of H2O2 under heat stress is mediated by the accumulation of endogenous polyamines. Moreover, compared with other treatments, the bitter-melon-grafted seedlings maintained high levels of antioxidant enzyme activity under high temperature conditions. However, these activities were significantly inhibited by polyamine synthesis inhibitors and H2O2 scavengers (dimethylthiourea, DMTU), indicating that bitter melon rootstock not only maintained better photosynthetic activity under conditions of high temperature stress but also mediated the production of H2O2 through the regulation of the high level of endogenous polyamines, thereby boosting the antioxidant defense system and comprehensively improving the heat tolerance of cucumber seedlings. Taken together, these results indicate that grafting with a resistant cultivar is a promising alternative tool for reducing stress-induced damage.

The Control of Developmental Phase Transitions by microRNAs and Their Targets in Seed Plants

Seed plants usually undergo various developmental phase transitions throughout their lifespan, mainly including juvenile-to-adult and vegetative-to-reproductive transitions, as well as developmental transitions within organ/tissue formation. MicroRNAs (miRNAs), as a class of small endogenous non-coding RNAs, are involved in the developmental phase transitions in plants by negatively regulating the expression of their target genes at the post-transcriptional level. In recent years, cumulative evidence has revealed that five miRNAs, miR156, miR159, miR166, miR172, and miR396, are key regulators of developmental phase transitions in plants. In this review, the advanced progress of the five miRNAs and their targets in regulating plant developmental transitions, especially in storage organ formation, are summarized and discussed, combining our own findings with the literature. In general, the functions of the five miRNAs and their targets are relatively conserved, but their functional divergences also emerge to some extent. In addition, potential research directions of miRNAs in regulating plant developmental phase transitions are prospected.

Molecular Responses during Plant Grafting and Its Regulation by Auxins, Cytokinins, and Gibberellins

Plant grafting is an important horticulture technique used to produce a new plant after joining rootstock and scion. This is one of the most used techniques by horticulturists to enhance the quality and production of various crops. Grafting helps in improving the health of plants, their yield, and the quality of plant products, along with the enhancement of their postharvest life. The main process responsible for successful production of grafted plants is the connection of vascular tissues. This step determines the success rate of grafts and hence needs to be studied in detail. There are many factors that regulate the connection of scion and stock, and plant hormones are of special interest for researchers in the recent times. These phytohormones act as signaling molecules and have the capability of translocation across the graft union. Plant hormones, mainly auxins, cytokinins, and gibberellins, play a major role in the regulation of various key physiological processes occurring at the grafting site. In the current review, we discuss the molecular mechanisms of graft development and the phytohormone-mediated regulation of the growth and development of graft union.

Inhibition of Methamphetamine Self-Administration and Reinstatement by Central Blockade of Angiotensin II Receptor in Rats

The molecular mechanism and treatment of methamphetamine (METH) use disorder remain unclear. The current study aimed to investigate the role of central angiotensin II receptor (ATR) in drug taking and seeking behavior associated with METH use disorder. The effect of an ATR type 1 (AT1R) antagonist, candesartan cilexetil, on the reinforcing and motivational effects of METH was first assessed using the animal model of METH self-administration (SA) and reinstatement. The levels of dopamine D2 receptor (D2R) and AT1R were subsequently examined. Furthermore, the present study determined the expression of microRNAs (miRNAs) by comparing METH SA, METH-yoked, and Saline-yoked groups. The target miRNAs were further overexpressed in the nucleus accumbens (NAc) via a lentivirus vector to investigate the effects of target miRNAs on METH SA maintained under a fixed ratio 1, progressive ratio, and cue/drug reinstatement of METH SA. The potential role of the AT1R-PLCβ-CREB signaling pathway was finally investigated. The results suggest that AT1R blockade effectively reduced METH SA and reinstatement, in conjunction with the counter-regulation of D2R and AT1R. A total of 17 miRNAs targeting Ang II in NAc were found to be associated with the voluntary intake of METH. Furthermore, overexpression of specific miR-219a-5p targeting AT1R-regulated METH SA and reinstatement. The AT1R-PLCβ-CREB signaling pathway was found to be associated with the effect of AT1R on the drug-taking and drug-seeking behavior involving METH use disorder.

Overexpression of the RNA binding protein MhYTP1 in transgenic apple enhances drought tolerance and WUE by improving ABA level under drought condition

MhYTP1 is involved in post-transcriptional regulation as a member of YT521-homology (YTH) domain-containing RNA-binding proteins. We previously cloned MhYTP1 and found it participated in various biotic and abiotic stress responses. However, its function in long-term moderate drought has not been verified. Thus, we explored its biological role in response to drought. Under drought condition, the net photosynthesis rate (P_n) and water use efficiency (WUE) were significantly elevated in MhYTP1-overexpressing (OE) apple plants when compared with the non-transgenic (NT) controls. Further analysis indicated MhYTP1 expression was associated with elevated ABA content, increased stomatal density and reduced stomatal aperture. In addition, to gain insight into the function of stem-specific expression of MhYTP1, grafting experiments were performed. Interestingly, lower transpiration rate (T_r) and higher WUE were observed when transgenic plants were used as scions as opposed to rootstocks and when transgenic rather than NT plants were used as rootstocks, indicating MhYTP1 plays crucial roles in grafted plants. These results define a function for MhYTP1 in promoting tolerance to drought conditions, and suggest that MhYTP1 can serve as a candidate gene for future apple drought resistance breeding with the help of biotechnology.

Redox and thylakoid membrane proteomic analysis reveals the Momordica (Momordica charantia L.) rootstock-induced photoprotection of cucumber leaves under short-term heat stress

Heat stress adversely affects plant physiological and metabolic processes and is considered an important constraint on crop growth and productivity in agriculture worldwide. Grafting techniques are capable of mitigating various stresses. Here, compared with self-grafted cucumbers subjected to 42 °C heat stress for 24 h, we found that Momordica-grafted cucumbers exhibited higher cytomembrane thermostability, less photoinhibition reflected by their chlorophyll fluorescence, and a reduction in oxidative stress. To better understand the mechanism, optimized Blue-Native/SDS-PAGE two-dimensional electrophoresis (2-DE) was firstly applied to entire thylakoid membrane of grafted cucumbers, and 25 significantly differential accumulated protein spots were identified by MALDI-TOF/TOF MS analysis. The proteomic analysis revealed that high temperatures suppressed the accumulation of 13 proteins in self-grafted cucumbers, while Momordica rootstock stimulated the accumulation of 12 of these proteins. The transcriptional analysis indicated that grafting onto Momordica significantly increased the expression of genes that encode the photosystem II subunit S (PsbS) and minor light-harvesting complexes (CP24, CP26 and CP29.1), which are closely associated with non-photochemical quenching (NPQ) after heat shock. Immunoblotting for PsbS corroborated the Momordica-induced acceleration of heat dissipation. Taken together, Momordica rootstock alleviated heat-induced photoinhibition by maintaining intracellular redox homeostasis, stabilizing the protein library of the thylakoid membrane and modulating NPQ in the scions.

Tiny Yet Indispensable Plant MicroRNAs Are Worth to Explore as Key Components for Combating Genotoxic Stresses

Plants being sessile are always exposed to various stresses including biotic and abiotic stresses. Some of these stresses are genotoxic to cells causing DNA damage by forming lesions which include altered bases, cross-links, and breaking of DNA strands, which in turn hamper the genomic integrity. In order to survive through all these adverse conditions, plants have evolved different DNA repair mechanisms. As seen from the mammalian system and different human diseases, various microRNAs (miRNAs) can target the 3'-untranslated region of mRNAs that code for the proteins involved in DNA repair pathways. Since miRNAs play an important role in plant cells by regulating various metabolic pathways, it can also be possible that miRNAs play an important role in DNA repair pathways too. However, till date, only a handful of plant miRNAs have been identified to play important role in combating genotoxic stresses in plants. Limitation of information regarding involvement of miRNAs in DNA repair as well as in ROS scavenging prompted us to gather information about plant miRNAs specific for these tasks. This mini-review aims to present pertinent literature dealing with different genotoxic stresses that cause genome instability as well as plant specific responses to survive the damage. This is intertwined with the involvement of miRNAs in genotoxic stress in plants, challenges of applying miRNAs as a tool to combat DNA damage along with ways to overcome these challenges, and finally, the future prospective of these understudied aspects.

Overexpression of CsCaM3 Improves High Temperature Tolerance in Cucumber

High temperature (HT) stress affects the growth and production of cucumbers, but genetic resources with high heat tolerance are very scarce in this crop. Calmodulin (CaM) has been confirmed to be related to the regulation of HT stress resistance in plants. CsCaM3, a CaM gene, was isolated from cucumber inbred line "02-8." Its expression was characterized in the present study. CsCaM3 transcripts differed among the organs and tissues of cucumber plants and could be induced by HTs or abscisic acid, but not by salicylic acid. CsCaM3 transcripts exhibited subcellular localization to the cytoplasm and nuclei of cells. Overexpression of CsCaM3 in cucumber plants has the potential to improve their heat tolerance and protect against oxidative damage and photosynthesis system damage by regulating the expression of HT-responsive genes in plants, including chlorophyll catabolism-related genes under HT stress. Taken together, our results provide useful insights into stress tolerance in cucumber.

Identification of microRNAs associated with the exogenous spermidine-mediated improvement of high-temperature tolerance in cucumber seedlings (Cucumis sativus L.)

BACKGROUND

High-temperature stress inhibited the growth of cucumber seedlings. Foliar spraying of 1.0 mmol·L- 1 exogenous spermidine (Spd) to the sensitive cucumber cultivar 'Jinchun No. 2' grown at high-temperature (42 °C/32 °C) in an artificial climate box improved the high-temperature tolerance. Although there have been many reports on the response of microRNAs (miRNAs) to high-temperature stress, the mechanism by which exogenous Spd may mitigate the damage of high-temperature stress through miRNA-mediated regulation has not been studied.

RESULTS

To elucidate the regulation of miRNAs in response to exogenous Spd-mediated improvement of high-temperature tolerance, four small RNA libraries were constructed from cucumber leaves and sequenced: untreated-control (CW), Spd-treated (CS), high-temperature stress (HW), and Spd-treated and high-temperature stress (HS). As a result, 107 known miRNAs and 79 novel miRNAs were identified. Eight common differentially expressed miRNAs (miR156d-3p, miR170-5p, miR2275-5p, miR394a, miR479b, miR5077, miR5222 and miR6475) were observed in CS/CW, HW/CW, HS/CW and HS/HW comparison pairs, which were the first set of miRNAs that responded to not only high-temperature stress but also exogenous Spd in cucumber seedlings. Five of the eight miRNAs were predicted to target 107 potential genes. Gene function and pathway analyses highlighted the integral role that these miRNAs and target genes probably play in the improvement of the high-temperature tolerance of cucumber seedlings through exogenous Spd application.

CONCLUSIONS

Our study identified the first set of miRNAs associated with the exogenous Spd-mediated improvement of high-temperature tolerance in cucumber seedlings. The results could help to promote further studies on the complex molecular mechanisms underlying high-temperature tolerance in cucumber and provide a theoretical basis for the high-quality and efficient cultivation of cucumber with high-temperature resistance.

Proteomic analysis of heat stress resistance of cucumber leaves when grafted onto Momordica rootstock

Various biotic and abiotic stresses threaten the cultivation of future agricultural crops. Among these stresses, heat stress is a major abiotic stress that substantially reduces agricultural productivity. Many strategies to enhance heat stress tolerance of crops have been developed, among which is grafting. Here, we show that Momordica-grafted cucumber scions have intrinsically enhanced chlorophyll content, leaf area, and net photosynthetic rate under heat stress compared to plants grafted onto cucumber rootstock. To investigate the mechanisms by which Momordica rootstock enhanced cucumber scions heat stress tolerance, comparative proteomic analysis of cucumber leaves in response to rootstock-grafting and/or heat stress was conducted. Seventy-seven differentially accumulated proteins involved in diverse biological processes were identified by two-dimensional electrophoresis (2-DE) in conjunction with matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometry (MALDI-TOF/TOF MS). The following four main categories of proteins were involved: photosynthesis (42.8%), energy and metabolism (18.2%), defense response (14.3%), and protein and nucleic acid biosynthesis (11.7%). Proteomic analysis revealed that scions grafted onto Momordica rootstocks upregulated more proteins involved in photosynthesis compared to scions grafted onto cucumber rootstocks under heat stress and indicated enhanced photosynthetic capacity when seedlings were exposed to heat stress. Furthermore, the expression of photosynthesis-related genes in plants grafted onto Momordica rootstocks significantly increased in response to heat stress. In addition, increased high-temperature tolerance of plants grafted onto Momordica rootstock was associated with the accumulation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and oxygen-evolving enhancer protein 1 (OEE1). Taken together, the data indicated that Momordica rootstock might alleviate growth inhibition caused by heat stress by improving photosynthesis, providing valuable insight into enhancing heat stress tolerance in the global warming epoch.

Small RNAs in regulating temperature stress response in plants

Due to global climate change, temperature stress has become one of the primary causes of crop losses worldwide. Much progress has been made in unraveling the complex stress response mechanisms in plants, particularly in the identification of temperature stress responsive protein-coding genes. Recently discovered microRNAs (miRNAs) and endogenous small-interfering RNAs (siRN As) have also been demonstrated as important players in plant temperature stress response. Using high-throughput sequencing, many small RNAs, especially miRNAs, have been identified to be triggered by cold or heat. Subsequently, several studies have shown an important functional role for these small RNAs in cold or heat tolerance. These findings greatly broaden our understanding of endogenous small RNAs in plant stress response control. Here, we highlight new findings regarding the roles of miRNAs and siRNAs in plant temperature stress response and acclimation. We also review the current understanding of the regulatory mechanisms of small RNAs in temperature stress response, and explore the outlook for the use of these small RNAs in molecular breeding for improvement of temperature stress tolerance in plants.

Grafting: A Technique to Modify Ion Accumulation in Horticultural Crops

Grafting is a centuries-old technique used in plants to obtain economic benefits. Grafting increases nutrient uptake and utilization efficiency in a number of plant species, including fruits, vegetables, and ornamentals. Selected rootstocks of the same species or close relatives are utilized in grafting. Rootstocks absorb more water and ions than self-rooted plants and transport these water and ions to the aboveground scion. Ion uptake is regulated by a complex communication mechanism between the scion and rootstock. Sugars, hormones, and miRNAs function as long-distance signaling molecules and regulate ion uptake and ion homeostasis by affecting the activity of ion transporters. This review summarizes available information on the effect of rootstock on nutrient uptake and utilization and the mechanisms involved. Information on specific nutrient-efficient rootstocks for different crops of commercial importance is also provided. Several other important approaches, such as interstocking (during double grafting), inarching, use of plant-growth-promoting rhizobacteria, use of arbuscular mycorrhizal fungi, use of plant growth substances (e.g., auxin and melatonin), and use of genetically engineered rootstocks and scions (transgrafting), are highlighted; these approaches can be combined with grafting to enhance nutrient uptake and utilization in commercially important plant species. Whether the rootstock and scion affect each other's soil microbiota and their effect on the nutrient absorption of rootstocks remain largely unknown. Similarly, the physiological and molecular bases of grafting, crease formation, and incompatibility are not fully identified and require investigation. Grafting in horticultural crops can help reveal the basic biology of grafting, the reasons for incompatibility, sensing, and signaling of nutrients, ion uptake and transport, and the mechanism of heavy metal accumulation and restriction in rootstocks. Ion transporter and miRNA-regulated nutrient studies have focused on model and non-grafted plants, and information on grafted plants is limited. Such information will improve the development of nutrient-efficient rootstocks.