Paleoenvironmental changes in the coastal zone of the northwest South China Sea during the last 13 kyr.

Marine sediments in coastal zones serve as valuable archives for understanding the history of silicate chemical weathering and summer monsoon rainfall in source areas, providing insights into terrigenous climate and environmental evolution. In this study, we investigated the grain size, clay minerals, and geochemistry of sediments retrieved from core KZK01 in the coastal zone of the northwest South China Sea during the past 13 thousand years before present (kyr BP). Our findings demonstrated that the illite crystallinity index served as a reliable proxy for assessing the intensity of chemical weathering in the source area. Moreover, it distinctly recorded significant climatic events such as the Younger Dryas and Bond events during the Holocene. The dominant driver of the regional East Asian summer monsoon was identified as summer solar radiation in the Northern Hemisphere at low latitudes. Cold climate events exhibited global consistency, potentially influenced by the presence of ice sheets at high latitudes. Lastly, our records revealed a distinct transition at 9.0 kyr, highlighting significant impacts of the Qiongzhou Strait and sea level rise on regional climate dynamics.

Identification, genetic diversity, and pathogenicity of Ralstonia pseudosolanacearum causing cigar tobacco bacterial wilt in China.

Ralstonia pseudosolanacearum, previously known as R. solanacearum species complex (RSSC) phylotypes I and III, is a plant pathogenic bacterium causing significant yield losses in economical crops. In the May of 2020 and 2021, cigar tobacco bacterial wilt was first observed in fields in Danzhou, Hainan Province, China. A total of eight bacterial isolates were isolated and identified as R. pseudosolanacearum with race 1, biovar III by 16S rRNA gene sequencing, Biolog, and host identification. The amino acid sequence showed that Hainan strains and 15 R. pseudosolanacearum reference strains from flue-cured tobacco in Shandong and Guizhou Provinces, all belonged to RS1000 type containing the avrA gene, only Guizhou strains also had the popP1 gene. On the basis of phylotype-specific multiplex PCR amplification, mismatch repair gene and endoglucanase gene-base tree, Hainan strains were identified as phylotype I sequevar 70, and showed stronger pathogenic capabilities on three different varieties than those reference strains. This is the first report of cigar tobacco bacterial wilt caused by R. pseudosolanacearum sequevar 70. The results revealed the diversity of RSSC in Nicotiana tabacum in China and provided useful information regarding the epidemiology of cigar tobacco wilt disease, as well as the breeding for disease resistance in local cigar tobacco.

Proteomic Analysis of Histone Crotonylation Suggests Diverse Functions in Myzus persicae.

Myzus persicae is one of the most important economic pests of cultivated crops. In the present study, we used an integrated approach involving high-performance liquid chromatography fractionation, affinity enrichment, and mass spectrometry-based proteomics to carry out a comprehensive proteomic analysis of lysine crotonylation in M. persicae. Altogether, 7530 lysine crotonylation sites were identified in 2452 protein groups. Intensive bioinformatic analyses were then carried out to annotate those lysine crotonylated targets identified in terms of Gene Ontology annotation, domain annotation, subcellular localization, Kyoto Encyclopedia of Genes and Genomes pathway annotation, functional cluster analysis, etc. Analysis results showed that lysine-crotonylated proteins were involved in many biological processes, such as the amino acid metabolism, aminoacyl-tRNA biosynthesis, spliceosomes, ribosomes, and so forth. Notably, the interaction network showed that there were 199 crotonylated proteins involved in the amino acid metabolism and numerous crotonylation targets associated with fatty acid biosynthesis and degradation. The results provide a system-wide view of the entire M. persicae crotonylome and a rich data set for functional analysis of crotonylated proteins in this economically important pest, which marks an important beginning for the further research.

Effects of Host-Adaptive Mutations on Hop Stunt Viroid Pathogenicity and Small RNA Biogenesis.

Accidental transmission of hop stunt viroid (HSVd) from grapevine to hop has led to several epidemics of hop stunt disease with convergent evolution of HSVd-g(rape) into HSVd-h(op) containing five mutations. However, the biological function of these five mutations remains unknown. In this study, we compare the biological property of HSVd-g and HSVd-h by bioassay and analyze HSVd-specific small RNA (HSVd-sRNA) using high-throughput sequencing. The bioassay indicated an association of these five mutations with differences in infectivity, replication capacity, and pathogenicity between HSVd-g and HSVd-h, e.g., HSVd-g induced more severe symptoms than HSVd-h in cucumber. Site-directed mutagenesis of HSVd-g showed that the mutation at position 54 increased pathogenicity. HSVd-sRNA analysis of cucumber and hop plants infected with different HSVd variants showed that several sRNA species containing adaptive nucleotides were specifically down-regulated in plants infected with HSVd-h. Several HSVd-sRNAs containing adaptive mutations were predicted to target cucumber genes, but changes in the levels of these genes were not directly correlated with changes in symptom expression. Furthermore, expression levels of two other cucumber genes targeted by HSVd-RNAs, encoding ethylene-responsive transcription factor ERF011, and trihelix transcription factor GTL2, were altered by HSVd infection. The possible relationship between these two genes to HSVd pathogenicity is discussed.

First Report of Cercospora nicotianae Causing Frog Eye Spot in Cigar Tobacco in Hainan, China.

Cigar tobacco (Nicotiana tabacum L.), sun air-cured tobacco, originally from South America, with a main use to rolling cigar wrapper that is different from flue-cured tobacco. In April, 2018, diseased leaves were observed in cigar tobacco in some fields in Danzhou city (109.58°E, 19.53°N) and Wuzhishan city (109.52°E, 18.78°N), Hainan. 20 to 40% of plants were infected (total 8 ha), thereby affecting local leaf production. The symptoms appeared as small, circular or irregular, sunken, brown patches developing into white centers and obvious dark brown margins with necrotic spots of 0.2-0.8 cm in most middle and lower leaves at mature stage. To determine the causal agent, ten leaves from five cigar tobacco plants (cv. Nuowei 2) collected from Danzhou were used for pathogen isolation (Fig. 1). Sections of infected leaf tissues were surface-sterilized by 5% NaClO for 3 min, 70% ethanol for 40 sec, rinsed in sterilized distilled water (SDW) and then placed onto potato dextrose agar (PDA) plates, under aseptic conditions and incubated at 28°C. After 7 days, predominant and consistent colonies that were nearly circular, smooth edges, generally hard, leathery and wrinkled surface, dense aerial hyphae, producing red pigment, were obtained and purified by picking hyphal tips to PDA at 28℃ (Fig. 2). One culture, HN4-1-7 from Hainan were deposited in Chinese General Microbial Cultural Center (CGMCC, NO. 3.19604). Frogeye lesions can be coved by tiny black dots on two sides and the fruiting bodies was amphigenous. Conidiophores were bluish yellow brown and gradually lighten at tips, 0-4 knee points, apical or subapical section, 0-14 septa, measured 45.1-506.4×2.3-11.7 µm in size. Conidia were needle-shaped to clavate, colorless, erect or curved, measured 37.2-169.6×1.9-5.5µm (Fig. 2). Further comparisons were completed with CGMCC 3.19604 by PCR and BLAST sequence analyses of the patial ITS rDNA region (GenBank accession nos. MK752900), TEF gene (GenBank accession nos. MK881748), ACT gene (GenBank accession nos. MK881749), CAL gene (GenBank accession nos. MT127561), and HIS gene (GenBank accession nos. MT185579) as described by Groenewald et al (2012). The results showed high identity of all the five sequences to the Cercospora nicotianae isolates, DQ835073, DQ835099, DQ835119, DQ835146, DQ835173. Based on the microscopic observation and molecular characteristics, isolate CGMCC 3.19604 were identified as C. nicotianae. The pathogenicity of CGMCC 3.19604 was evaluated in greenhouse experiments. Twenty sixty-day old cigar tobacco leaves (cv. H211) and flue cured tobacco leaves (Honghuadajinyuan) were sprayed with hyphae suspensions of CGMCC, NO. 3.19604 until runoff, respectively, and the experiment was repeated once. For controls, leaves of two cultivars were similarly wounded and inoculated with SDW. All plants were incubated under 90% humidity and 28°C with a 12 h photoperiod/day. After 9 days, the same diseased symptom (Fig.3) was observed on inoculated leaves of cigar tobacco were identical to the natural infected leaves respectively, but not on control leaves. C. nicotianae was re-isolated from lesions by cultural and morphological characteristics, fufilling Koch's postulates. All tests were repeated once. To the best of our knowledge, this is the first report of C. nicotianae causing frog eye spot in cigar tobacco in Hainan, China. As we all known, appearance integrity and uniformity are playing an important role in high quality of cigar-wrapper, but the incidence of frog eye spot can seriously affect appearance quality of cigar-wrapper and led to increase direct losses to local cigar tobacco production. In addition, symptom of frog eye spot is similar to brown spot disease caused by Alternaria alternata, often cause their symptoms confused and then delay prevention at the right time. Since the cigar tobacco is a major industry in Hainan, better understanding of its diseases is relevant in order to establish disease control strategies.

Identification of Genes/Proteins Related to Submergence Tolerance by Transcriptome and Proteome Analyses in Soybean.

Flooding can lead to yield reduction of soybean. Therefore, identification of flooding tolerance genes has great significance in production practice. In this study, Qihuang 34, a highly-resistant variety to flooding stress, was selected for submergence treatments. Transcriptome and proteome analyses were conducted, by which twenty-two up-regulated differentially expressed genes (DEGs)/differentially expressed proteins (DEPs) associated with five KEGG pathways were isolated. The number of the DEGs/DEPs enriched in glycolysis/gluconeogenesis was the highest. Four of these genes were confirmed by RT-qPCR, suggesting that glycolysis/gluconeogenesis may be activated to generate energy for plant survival under anaerobic conditions. Thirty-eight down-regulated DEGs/DEPs associated with six KEGG pathways were identified under submergence stress. Eight DEGs/DEPs enriched in phenylpropanoid biosynthesis were assigned to peroxidase, which catalyzes the conversion of coumaryl alcohol to hydroxy-phenyl lignin in the final step of lignin biosynthesis. Three of these genes were confirmed by RT-qPCR. The decreased expression of these genes led to the inhibition of lignin biosynthesis, which may be the cause of plant softening under submergence stress for a long period of time. This study revealed a number of up-/down-regulated pathways and the corresponding DEGs/DEPs, by which, a better understanding of the mechanisms of submergence tolerance in soybean may be achieved.

Global Transcriptomic Changes Induced by Infection of Cucumber (Cucumis sativus L.) with Mild and Severe Variants of Hop Stunt Viroid.

Fifteen years after transfer to hops, hop stunt viroid-grapevine (HSVd-g) was replaced by HSVd-hop (HSVd-h), a sequence variant that contains changes at five different positions. HSVd-g54 is a laboratory mutant derived from HSVd-g that differs from its progenitor by a single G to A substitution at position 54. While infection by HSVd-h induces only mild stunting in cucumber (Cucumis sativus L.), HSVd-g54 induces much more severe symptoms in this indicator host. Comparison of transcriptome profiles of cucumber infected with HSVd-h or HSVd-g54 with those of mock-inoculated controls obtained by whole transcriptome shotgun sequencing revealed that many genes related to photosynthesis were down-regulated following infection. In contrast, genes encoding RNA-dependent RNA polymerase 1 (CsRDR1), especially CsRDR1c1 and CsRDR1c2, as well as those related to basal defense responses were up-regulated. Expression of genes associated with phytohormone signaling pathways were also altered, indicating that viroid infection initiates a complex array of changes in the host transcriptome. HSVd-g54 induced an earlier and stronger response than HSVd-h, and further examination of these differences will contribute to a better understanding of the mechanisms that determine viroid pathogenicity.

Stem Rot on Adzuki Bean (Vigna angularis) Caused by Rhizoctonia solani AG 4 HGI in China.

During late August and early September 2011, stem rot symptoms were observed on adzuki bean plants (Vigna angularis) growing in fields located in Beijing and Hebei Province, China, respectively. In this study, four isolates were obtained from infected stems of adzuki bean plants. Based on their morphology, and sequence and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analyses of the ribosomal DNA internal transcribed spacers (rDNA-ITS) region, the four isolates were identified as Rhizoctonia solani in anastomosis group (AG) 4 HGI. Pathogenicity tests showed that all isolates were strongly pathogenic to adzuki bean and resulted in serious wilt symptoms which was similar to observations in the fields. Additionally, the isolates infected several other crops and induced related rot on the roots and basal stems. To our knowledge, this is the first report of Rhizoctonia solani AG 4 HGI causing stem rot on adzuki bean.

Identification and candidate gene analysis of a novel phytophthora resistance gene Rps10 in a Chinese soybean cultivar.

Resistance to Phytophthora sojae isolate PsMC1 was evaluated in 102 F2∶3 families derived from a cross between the resistant soybean cultivar Wandou 15 and the susceptible cultivar Williams and genotyped using simple sequence repeat (SSR) markers. The segregation ratio of resistant, segregating, and susceptible phenotypes in the population suggested that the resistance in Wandou 15 was dominant and monogenic. Twenty-six polymorphic SSR markers were identified on soybean chromosome 17 (Molecular linkage group D2; MLG D2), which were linked to the resistance gene based on bulked segregation analysis (BSA). Markers Sattwd15-24/25 and Sattwd15-47 flanked the resistance gene at a distance of 0.5 cM and 0.8 cM, respectively. Two cosegregating markers, Sattwd15-28 and Sattwd15-32, were also screened in this region. This is the first Rps resistance gene mapped on chromosome 17, which is designated as Rps10. Eight putative genes were found in the mapped region between markers Sattwd15-24/25 and Sattwd15-47. Among them, two candidate genes encoding serine/threonine (Ser/Thr) protein kinases in Wandou 15 and Williams were identified and sequenced. And the differences in genomic sequence and the putative amino acid sequence, respectively, were identified within each candidate gene between Wandou 15 and Williams. This novel gene Rps10 and the linked markers should be useful in developing soybean cultivars with durable resistance to P. sojae.

Genetic characterization and fine mapping of the novel Phytophthora resistance gene in a Chinese soybean cultivar.

Phytophthora root rot (PRR), caused by Phytophthora sojae Kaufmann & Gerdemann, is one of the most destructive diseases of soybean [Glycine max (L.) Merr.]. Deployment of resistance genes is the most economical and effective way of controlling the disease. The soybean cultivar 'Yudou 29' is resistant to many P. sojae isolates in China. The genetic basis of the resistance in 'Yudou 29' was elucidated through an inheritance study and molecular mapping. In response to 25 P. sojae isolates, 'Yudou 29' displayed a new resistance reaction pattern distinct from those of differentials carrying known Rps genes. A population of 214 F2:3 families from a cross between 'Jikedou 2' (PRR susceptible) and 'Yudou 29' was used for Rps gene mapping. The segregation fit a ratio of 1:2:1 for resistance:segregation:susceptibility within this population, indicating that resistance in 'Yudou 29' is controlled by a single dominant gene. This gene was temporarily named RpsYD29 and mapped on soybean chromosome 03 (molecular linkage group N; MLG N) flanked by SSR markers SattWM82-50 and Satt1k4b at a genetic distance of 0.5 and 0.2 cM, respectively. Two nucleotide binding site-leucine rich repeat (NBS-LRR) type genes were detected in the 204.8 kb region between SattWM82-50 and Satt1k4b. These two genes showed high similarity to Rps1k in amino acid sequence and could be candidate genes for PRR resistance. Based on the phenotype reactions and the physical position on soybean chromosome 03, RpsYD29 might be a novel allele at, or a novel gene tightly linked to, the Rps1 locus.