Efficient Polyamine-Based Nanodelivery System for Proline: Enhanced Uptake Improves the Drought Tolerance of Tobacco.

Drought stress is one of the most unfavorable factors affecting plant growth and productivity among various environmental stresses. Nanotechnology is expected to enhance the effectiveness of conventional biostimulants. Herein, the current study constructed an efficient proline (Pro) nanodelivery system based on a star polyamine (SPc). The hydroxyl groups of Pro could assemble with carbonyl groups of SPc, and the self-assembly of Pro with SPc formed the nanoscale particles of the Pro/SPc complex. Compared to Pro alone, the contact angle of SPc-loaded Pro decreased, and its retentivity and plant uptake increased. Importantly, the tobacco (Nicotiana benthamiana) seeds and seedlings treated with Pro/SPc complex exhibited stronger drought tolerance. RNA-Seq analysis indicated that the SPc-loaded Pro could further upregulate photosynthesis-related genes and endocytosis-related genes. The current study constructed an efficient nanodelivery system for improving the bioactivity of biostimulants, which has broad application prospects in the agricultural field.

Genome-Wide Identification of DUF668 Gene Family and Expression Analysis under Drought and Salt Stresses in Sweet Potato [Ipomoea batatas (L.) Lam].

The domain of unknown function 668 (DUF668) is a gene family that plays a vital role in responses to adversity coercion stresses in plant. However, the function of the DUF668 gene family is not fully understood in sweet potato. In this study, bioinformatics methods were used to analyze the number, physicochemical properties, evolution, structure, and promoter cis-acting elements of the IbDUF668 family genes, and RNA-seq and qRT-PCR were performed to detect gene expression and their regulation under hormonal and abiotic stress. A total of 14 IbDUF668 proteins were identified in sweet potato, distributed on nine chromosomes. By phylogenetic analysis, IbDUF668 proteins can be divided into two subfamilies. Transcriptome expression profiling revealed that many genes from DUF668 in sweet potato showed specificity and differential expression under cold, heat, drought, salt and hormones (ABA, GA3 and IAA). Four genes (IbDUF668-6, 7, 11 and 13) of sweet potato were significantly upregulated by qRT-PCR under ABA, drought and NaCl stress. Results suggest that the DUF668 gene family is involved in drought and salt tolerance in sweet potato, and it will further provide the basic information of DUF668 gene mechanisms in plants.

Current advances in the identification of plant nematode diseases: From lab assays to in-field diagnostics.

Plant parasitic nematodes (PPNs) cause an important class of diseases that occur in almost all types of crops, seriously affecting yield and quality and causing great economic losses. Accurate and rapid diagnosis of nematodes is the basis for their control. PPNs often have interspecific overlays and large intraspecific variations in morphology, therefore identification is difficult based on morphological characters alone. Instead, molecular approaches have been developed to complement morphology-based approaches and/or avoid these issues with various degrees of achievement. A large number of PPNs species have been successfully detected by biochemical and molecular techniques. Newly developed isothermal amplification technologies and remote sensing methods have been recently introduced to diagnose PPNs directly in the field. These methods have been useful because they are fast, accurate, and cost-effective, but the use of integrative diagnosis, which combines remote sensing and molecular methods, is more appropriate in the field. In this paper, we review the latest research advances and the status of diagnostic approaches and techniques for PPNs, with the goal of improving PPNs identification and detection.

Transcriptomic analysis reveals mechanisms for the different drought tolerance of sweet potatoes.

Drought is a common environmental stress with great negative impacts on plant growth, development and geographical distribution as well as agriculture and food production. Sweet potato is characterized by starchy, fresh and pigmented tuber, and is regarded as the seventh most important food crop. However, there has been no comprehensive study of the drought tolerance mechanism of different sweet potato cultivars to date. Here, we studied the mechanism for drought response of seven sweet potato drought-tolerant cultivars using the drought coefficients, physiological indicators and transcriptome sequencing. The seven sweet potato cultivars were classified into four groups of drought tolerance performance. A large number of new genes and transcripts were identified, with an average of about 8000 new genes per sample. Alternative splicing events in sweet potato, which were dominated by first exon and last exon alternative splicing, were not conserved among different cultivars and not significantly affected by drought stress. Furthermore, different drought-tolerance mechanisms were revealed through differentially expressed gene analysis and functional annotation. Two drought-sensitive cultivars, Shangshu-9 and Xushu-22, mainly resisted drought stress by up-regulating plant signal transduction. The other drought-sensitive cultivar Jishu-26 responded to drought stress by down-regulating isoquinoline alkaloid biosynthesis and nitrogen/carbohydrate metabolism. In addition, the drought-tolerant cultivar Chaoshu-1 and drought-preferred cultivar Z15-1 only shared 9% of differentially expressed genes, as well as many opposite metabolic pathways in response to drought. They mainly regulated flavonoid and carbohydrate biosynthesis/metabolism in response to drought, while Z15-1 increased photosynthesis and carbon fixation capacity. The other drought-tolerant cultivar Xushu-18 responded to drought stress by regulating the isoquinoline alkaloid biosynthesis and nitrogen/carbohydrate metabolism. The extremely drought-tolerant cultivar Xuzi-8 was almost unaffected by drought stress and responded to drought environment only by regulating the cell wall. These findings provide important information for the selection of sweet potatoes for specific purposes.

Characterization of a Novel Insect-Induced Sesquiterpene Synthase GbTPS1 Based on the Transcriptome of Gossypium barbadense Feeding by Cotton Bollworm.

When attacked by insect herbivores, plants initiate sophisticated defenses mediated by complex signaling networks and usually release a blend of functional volatiles such as terpenes against infestation. The extra-long staple cotton Gossypium barbadense cultivated worldwide as natural textile fiber crop is frequently exposed to a variety of herbivores, such as cotton bollworm Helicoverpa armigera. However, little is known about insect-induced transcriptional changes and molecular mechanisms underlying subsequent defense responses in G. barbadense. In the current study, transcriptome changes in G. barbadense infested with chewing H. armigera larvae were investigated, and we identified 5,629 differentially expressed genes (DEGs) in the infested cotton leaves compared with non-infested controls. H. armigera feeding triggered complex signaling networks in which almost all (88 out of 90) DEGs associated with the jasmonic acid (JA) pathway were upregulated, highlighting a central role for JA in the defense responses of G. barbadense against target insects. All DEGs involved in growth-related photosynthesis were downregulated, whereas most DEGs associated with defense-related transcript factors and volatile secondary metabolism were upregulated. It was noteworthy that a terpene synthase gene in the transcriptome data, GbTPS1, was strongly expressed in H. armigera-infested G. barbadense leaves. The upregulation of GbTPS1 in qPCR analysis also suggested an important role for GbTPS1 in herbivore-induced cotton defense. In vitro assays showed that recombinant GbTPS1 catalyzed farnesyl pyrophosphate and neryl diphosphate to produce three sesquiterpenes (selinene, α-gurjunene, and ß-elemene) and one monoterpene (limonene), respectively. Moreover, these catalytic products of GbTPS1 were significantly elevated in G. barbadense leaves after H. armigera infestation, and elemene and limonene had repellent effects on H. armigera larvae in a dual-choice bioassay and increased larval mortality in a no-choice bioassay. These findings provide a valuable insight into understanding the transcriptional changes reprogramming herbivore-induced sesquiterpene biosynthesis in G. barbadense infested by H. armigera, which help elucidate the molecular mechanisms underlying plant defense against insect pests.

The heat shock factor GhHSFA4a positively regulates cotton resistance to Verticillium dahliae.

Heat shock factors (HSFs) play a crucial role in the environmental stress responses of numerous plant species, including defense responses to pathogens; however, their role in cotton resistance to Verticillium dahliae remains unclear. We have previously identified several differentially expressed genes (DEGs) in Arabidopsis thaliana after inoculation with V. dahliae. Here, we discovered that GhHSFA4a in Gossypium hirsutum (cotton) after inoculation with V. dahliae shares a high identity with a DEG in A. thaliana in response to V. dahliae infection. Quantitative real-time PCR (qRT-PCR) analysis indicated that GhHSFA4a expression was rapidly induced by V. dahliae and ubiquitous in cotton roots, stems, and leaves. In a localization analysis using transient expression, GhHSFA4a was shown to be localized to the nucleus. Virus-induced gene silencing (VIGS) revealed that downregulation of GhHSFA4a significantly increased cotton susceptibility to V. dahliae. To investigate GhHSFA4a-mediated defense, 814 DEGs were identified between GhHSFA4a-silenced plants and controls using comparative RNA-seq analysis. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that DEGs were enriched in "flavonoid biosynthesis", "sesquiterpenoid and triterpenoid biosynthesis", "linoleic acid metabolism" and "alpha-linolenic acid metabolism". The expression levels of marker genes for these four pathways were triggered after inoculation with V. dahliae. Moreover, GhHSFA4a-overexpressing lines of A. thaliana displayed enhanced resistance against V. dahliae compared to that of the wild type. These results indicate that GhHSFA4a is involved in the synthesis of secondary metabolites and signal transduction, which are indispensable for innate immunity against V. dahliae in cotton.

A droplet digital PCR assay for detection and quantification of Verticillium nonalfalfae and V. albo-atrum.

Verticillium nonalfalfae and V. albo-atrum are notorious pathogenic fungi that cause a destructive vascular disease called Verticillium wilt worldwide. Thus, timely and quantitative monitoring of fungal progression is highly desirable for early diagnosis and risk assessment. In this study, we developed a droplet digital polymerase chain reaction (ddPCR) assay to detect and quantify V. nonalfalfae and V. albo-atrum. The performance of this assay was validated in comparison with that of a quantitative real-time polymerase chain reaction (qPCR) assay. The standard curve analysis of the ddPCR assay showed good linearity. The ddPCR assay indicated similar detection sensitivity to that of qPCR on pure genomic DNA, while it enhanced the positive rate for low-abundance fungi, especially in alfalfa stems. Receiver operating characteristic analysis revealed that ddPCR provided superior diagnostic performance on field tissues compared to qPCR, and the area under curve values were 0.94 and 0.90 for alfalfa roots and stems, respectively. Additionally, the quantitative results of the two methods were highly concordant (roots: R2 = 0.91; stems: R2 = 0.76); however, the concentrations determined by ddPCR were generally higher than those determined by qPCR. This discrepancy was potentially caused by differing amplification efficiencies for qPCR between cultured and field samples. Furthermore, the ddPCR assays appreciably improved quantitative precision, as reflected by lower coefficients of variation. Overall, the ddPCR method enables sensitive detection and accurate quantification of V. nonalfalfae and V. albo-atrum, providing a valuable tool for evaluating disease progression and enacting effective disease control.

Functional characterization of a terpene synthase responsible for (E)-ß-ocimene biosynthesis identified in Pyrus betuleafolia transcriptome after herbivory.

(E)-ß-ocimene, a ubiquitous monoterpene volatile in plants, is emitted from flowers to attract pollinators and/or from vegetative tissues as part of inducible defenses mediated by complex signaling networks when plants are attacked by insect herbivores. Wild pear species Pyrus betuleafolia used worldwide as rootstock generally displays valuable pest-resistant traits and is a promising genetic resource for pear breeding. In the current study, transcriptional changes in this wild pear species infested with a polyphagous herbivore Spodoptera litura and the underlying molecular mechanisms were fully investigated. A total of 3,118 differentially expressed genes (DEGs) were identified in damaged pear leaf samples. Spodoptera litura larvae infestation activated complex phytohormonal signaling networks in which jasmonic acid, ethylene, brassinosteroids, cytokinin, gibberellic acid and auxin pathways were induced, whereas salicylic acid and abscisic acid pathways were suppressed. All DEGs associated with growth-related photosynthesis were significantly downregulated, whereas most DEGs involved in defense-related early signaling events, transcription factors, green leaf volatiles and volatile terpenes were significantly upregulated. The PbeOCS (GWHGAAYT028729), a putative (E)-ß-ocimene synthase gene, was newly identified in P. betuleafolia transcriptome. The upregulation of PbeOCS in S. litura-infested pear leaves supports a potential role for PbeOCS in herbivore-induced plant defenses. In enzyme-catalyzed reaction, recombinant PbeOCS utilized only geranyl pyrophosphate but not neryl diphosphate, farnesyl pyrophosphate or geranylgeranyl diphosphate as a substrate, producing (E)-ß-ocimene as the major product and a trace amount of (Z)-ß-ocimene. Moreover, as a catalytic product of PbeOCS, (E)-ß-ocimene showed repellent effects on larvae of S. litura in dual-choice bioassays. What is more, (E)-ß-ocimene increased mortalities of larvae in no-choice bioassays. These findings provide an overview of transcriptomic changes in wild pears in response to chewing herbivores and insights into (E)-ß-ocimene biosynthesis in pear plants, which will help elucidate the molecular mechanisms underlying pear-insect interactions.

A Preparation Method of Nano-Pesticide Improves the Selective Toxicity toward Natural Enemies.

Various nano-delivery systems have been designed to deliver synthetic/botanical pesticides for improved bioactivity. However, the enhanced toxicity of nanocarrier-loaded pesticides may injure the natural enemies, and their selective toxicity should be evaluated before the large-scale application. In this context, a star polymer (SPc)-based cyantraniliprole (CNAP) nano-delivery system was constructed, and its selective toxicity was evaluated using pest Frankliniella occidentalis (WFT) and predator Orius sauteri. The amide NH of CNAP could assemble with carbonyl groups or tertiary amines of SPc through hydrogen bonds to form CNAP/SPc complex spontaneously. The above self-assembly decreased the particle size of CNAP from 808 to 299 nm. With the help of SPc, the lethal concentration 50 (LC50) values of CNAP decreased from 99 to 54 mg/L and 230 to 173 mg/L toward WFTs and O. sauteri due to the enhancement of broad-spectrum bioactivity. Interestingly, the toxicity selective ratio (TSR) of CNAP increased from 2.33 to 3.23 with the help of SPc, revealing the higher selectivity of SPc-loaded CNAP. To our knowledge, it was the first successful exploration of the selective toxicity of nanocarrier-loaded pesticides, and the higher selective toxicity of SPc-loaded CNAP was beneficial for alleviating the negative impacts on predators.

Field evolved resistance to pyrethroids, neonicotinoids, organophosphates and macrolides in Rhopalosiphum padi (Linnaeus) and Sitobion avenae (Fabricius) from China.

Rhopalosiphum padi (Linnaeus) and Sitobion avenae (Fabricius) are the predominant pests coexisting on wheat plants. In this study, the susceptibilities of 29 R. padi and 30 S. avenae populations from 15 provinces in China to pyrethroids (beta-cypermethrin and bifenthrin), neonicotinoids (imidacloprid and thiamethoxam), organophosphates (omethoate and chlorpyrifos) and macrolides (avermectin) were determined during 2018-2019. The median lethal insecticide concentrations (LC50) indicated that R. padi was more sensitive than S. avenae to most of the insecticides. Monitor results showed that most wheat aphid populations were moderately resistant to pyrethroids. Two R. padi populations were highly resistant to beta-cypermethrin with 127.3-fold and 442.8-fold resistance ratio (RR), and two were highly resistant to bifenthrin (RR of 293.9 and 320.6, respectively). One S. avenae population was highly resistant to beta-cypermethrin (RR of 136.8) and one was highly resistant to bifenthrin (RR of 313.4). All populations of two wheat aphids exhibited low to moderate resistance to neonicotinoids (RR < 100). But over half populations were sensitive or exhibited low resistance to organophosphates and macrolides. The pair-wise correlation coefficients for the insecticide LC50 revealed a positive correlation between beta-cypermethrin and bifenthrin resistance, as well as between the resistance to bifenthrin and omethoate for the two-aphid species. Similarly, significant correlations were detected between the resistance to beta-cypermethrin and avermectin for R. padi. These results may be relevant for developing effective insecticide management strategies that prevent or delay the development of resistance among wheat aphids.