Food is a fundamental human right, and global food security is threatened by crop production. Plant growth regulators (PGRs) play an essential role in improving crop yield and quality, and this study reports on a novel PGR, termed guvermectin (GV), isolated from plant growth-promoting rhizobacteria, which can promote root and coleoptile growth, tillering, and early maturing in rice. GV is a nucleoside analogue like cytokinin (CK), but it was found that GV significantly promoted root and hypocotyl growth, which is different from the function of CK in Arabidopsis. The Arabidopsis CK receptor triple mutant ahk2-2 ahk3-3 cre1-12 still showed a GV response. Moreover, GV led different growth-promoting traits from auxin, gibberellin (GA), and brassinosteroid (BR) in Arabidopsis and rice. The results from a four-year field trial involving 28 rice varieties showed that seed-soaking treatment with GV increased the yields by 6.2 to 19.6%, outperforming the 4.0 to 10.8% for CK, 1.6 to 16.9% for BR, and 2.2 to 7.1% for GA-auxin-BR mixture. Transcriptome analysis demonstrated that GV induced different transcriptome patterns from CK, auxin, BR, and GA, and SAUR genes may regulate GV-mediated plant growth and development. This study suggests that GV represents a novel PGR with a unique signal perception and transduction pathway in plants.
Maize is a major economic crop worldwide. Maize can be infected by Alternaria species causing leaf blight that can result in significant economic losses. In this study, 168 Alternaria isolates recovered from symptomatic maize leaves were identified based on morphological characteristics, pathogenicity, and multi-locus sequence analyses of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), the internal transcribed spacer of ribosomal DNA (rDNA ITS), the RNA polymerase II second largest subunit (RPB2), and histone 3 (HIS3). Maize isolates grouped to four Alternaria species including Alternaria tenuissima, A. alternata, A. burnsii, and Alternaria sp. Notably, A. tenuissima (71.4%) was the most prevalent of the four isolated species, followed by A. alternata (21.5%), Alternaria sp. (4.1%), and A. burnsii (3.0%). Pathogenicity tests showed that all four Alternaria species could produce elliptic to nearly round, or strip lesions on leaves of maize, gray white to dry white in the lesions center and reddish brown in the edge. The average disease incidence (58.47%) and average disease index (63.55) of maize leaves inoculated with A. alternata were significantly higher than levels resulting from A. tenuissima (55.28% and 58.49), Alternaria sp. (55.34% and 58.75), and A. burnsii (56% and 55). Haplotype analyses indicated that there were 14 haplotypes of A. tenuissima and 5 haplotypes of A. alternata in Heilongjiang province and suggested the occurrence of a population expansion. Results of the study showed that Alternaria species associated with maize leaf blight in Heilongjiang province are more diverse than those have been previously reported. This is the first report globally of A. tenuissima, A. burnsii, and an unclassified Alternaria species as causal agents of leaf blight on maize.
Maize (Zea mays L.) is a chilling-sensitive plant. Chilling stress in the early seedling stage seriously limits the growth, development, productivity and geographic distribution of maize. Salicylic acid (SA) is a plant growth regulator involved in the defenses against abiotic and biotic stresses as well as in plant development. However, the physiological mechanisms underlying the effects of foliar applied SA on different maize inbred lines under chilling stress are unclear. Two inbred lines, cold-sensitive cv. C546 and cold-tolerant cv. B125, were used to study the effects of SA on the growth and physiology of maize seedlings. The results showed that the application of SA at 50 mg/L on the leaves of maize seedlings under 4 °C decreased the relative electrolyte conductivity (REC) and the malondialdehyde (MDA) and reactive oxygen species (ROS) (H2O2 and O2−) content due to increased superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) activity; SA also improved photosynthesis in the seedlings through increased chlorophyll content, enhanced Pn and Gs, and decreased Ci. SA application also increased the proline content and the relative water content (RWC) in the maize seedlings, thereby improving their osmotic adjustment capacity. The increase rate caused by SA of plant height and dry weight in C546 were 10.5% and 5.4% higher than that in B125 under 4 °C. In conclusion, SA promotes maize seedling growth and physiological characteristics, thus enhancing chilling resistance and the effect of SA on the chilling resistance of cold-sensitive cv. was stronger than that on cold-tolerant cv. at the low temperature.
Maize (Zea mays L.) is the most important crop in Heilongjiang province. In July 2021, maize stalk rot was observed on approximately 10% of maize in a 2.4 ha field of Xiangfang District, Harbin City (N45°44'23″, E126°43'19″). Infected plants showed softening of the stalks at the lower internodes, and the pith tissue was disintegrated and brown to reddish. Fifteen symptomatic plants were collected from the field. The discolored stalk pith tissues were cut into small pieces (4 × 2 mm), superficially disinfected with 1% NaClO for 3 min, 70% ethanol for 10 s, and then washed three times with sterile distilled water. The disinfected tissues were placed on potato dextrose agar (PDA) amended with streptomycin sulfate (50 mg/L) and incubated at 25°C for 1 week. Twenty-one cultures were obtained using hyphal tip technology and cultured on PDA for 7 days at 25°C for morphological and molecular analyses. The mycelia of the cultures were initially white but became grayish with time, and reddish-brown diffusible pigments were produced. A dark green discoloration was produced on malt extract agar (MEA) using the NaOH spot test (REF). Pycnidia were brown, predominantly spheroidal, and measured 80.1 to 130.2 × 110.5 to 220.6 μm. Conidia were ellipse, aseptate, and in a size range of 4.3 to 6.8 × 2.1 to 3.2 μm. The isolates were initially identified as Epicoccum latusicollum based on morphological features (Chen et al. 2017). To confirm the identity of E. latusicollum, primers TUB2Fd/TUB4Rd, LR0R/LR5, ITS1/ITS4 and RPB2-5F2/fRPB2-7cR (Valenzuela-Lopez et al. 2018) were used to amplify beta tubulin (tub2), nuclear large subunit rDNA (LSU), internal transcribed spacer (ITS), and RPB2 genes, respectively for the representative isolate JF3. These sequences were deposited in GenBank (GenBank accession no. OK490498, OK445527, OK483136, and OK490497) and had 100% (276/276 bp), 100% (842/842 bp), 100% (501/501 bp), and 100% (589/589 bp) nucleotide identity with E. latusicollum isolate GZDS2018BXT010 (GenBank accession no. MK516208, MK516207, MK516206, and MK852278). To fulfill Koch’s postulates, pathogenicity tests for all isolates were performed by individually inoculating surface-disinfected stalks of five healthy maize plants (10-leaf stage) between the 2nd and 3rd stem nodes with 20 μL conidial suspension at a concentration of 106 conidia/mL as described by Zhang et al. (2016). Five other healthy surface-disinfected maize plants inoculated with sterile distilled water served as control. All plants were kept at 25 ± 0.5°C in a greenhouse with a photoperiod of 12 h and approximately 90% relative humidity. After 10 days, all inoculated plants showed symptoms that were similar to those of the infected maize plants observed in the field, whereas the control plants were asymptomatic. The Epicoccum isoaltes were re-isolated from symptomatic plants, and species identification was performed using the morphological and molecular methods described above. To our knowledge, this is the first report of E. latusicollum causing maize stalk rot in China, and this report will assist with monitoring distribution of the disease and developing management recommendations.
Febrifugine, a natural alkaloid, exhibits specific anti-phytophthora activity; however, its mode of action is unclear. In this study, halofuginone, a synthetic derivative of febrifugine, showed significantly higher anti-phytophthora activities than those of febrifugine and the commercial drug metalaxyl against Phytophthora sojae, Phytophthora capsici, and Phytophthora infestans with effective concentration for 50% inhibition (EC50) values of 0.665, 0.673, and 0.178 μg/mL, respectively. Proline could alleviate the growth inhibition of halofuginone on P. capsici, implying that halofuginone might target prolyl-tRNA synthetase (PcPRS). The anti-phytophthora mechanism of halofuginone was then investigated by molecular docking, fluorescence titration, and enzymatic inhibition assays. The results revealed that halofuginone could bind to PcPRS and shared a similar binding site with the substrate proline. Point mutations at Glu316 and Arg345 led to 24.5 and 16.1% decreases in the enzymatic activity of PcPRS but 816.742- and 459.557-fold increases in the resistance to halofuginone, respectively. The results further confirmed that halofuginone was a competitive inhibitor of proline against PcPRS, and Glu316 and Arg345 played important roles in the binding of halofuginone and proline. Taken together, the results indicated that halofuginone is an alternative anti-phytophthora drug candidate and that PcPRS represents a potential target for the development of new pesticides.
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