Enhanced cytokinin signaling results in delayed defoliation and a reduced response to ethylene in cotton treated with thidiazuron and ethephon, with crosstalk between cytokinin and ethylene signaling playing an important regulatory role.
Summary
Bacterial wilt caused by Ralstonia solanacearum is a complex and destructive disease that affects over 200 plant species. To investigate the interaction of R. solanacearum and its tomato (Solanum lycopersicum) plant host, a comparative proteomic analysis was conducted in tomato stems inoculated with highly and mildly aggressive R. solanacearum isolates (RsH and RsM, respectively). The results indicated a significant alteration of the methionine cycle (MTC) and downregulation of γ‐aminobutyric acid (GABA) biosynthesis. Furthermore, transcriptome profiling of two key tissues (stem and root) at three stages (0, 3 and 5 days post‐inoculation) with RsH in resistant and susceptible tomato plants is presented. Transcript profiles of MTC and GABA pathways were analyzed. Subsequently, the MTC‐associated genes SAMS2, SAHH1 and MS1 and the GABA biosynthesis‐related genes GAD2 and SSADH1 were knocked‐down by virus‐induced gene silencing and the plants’ defense responses upon infection with R. solanacearum RsM and RsH were analyzed. These results showed that silencing of SAHH1, MS1 and GAD2 in tomato leads to decreased resistance against R. solanacearum. In summary, the infection assays, proteomic and transcriptomic data described in this study indicate that both MTC and GABA biosynthesis play an important role in pathogenic interaction between R. solanacearum and tomato plants.
Sea Island cotton (Gossypium barbadense) is the source of the world's finest fibre quality cotton, yet relatively little is understood about genetic variations among diverse germplasms, genes underlying important traits and the effects of pedigree selection. Here, we resequenced 336 G. barbadense accessions and identified 16 million SNPs. Phylogenetic and population structure analyses revealed two major gene pools and a third admixed subgroup derived from geographical dissemination and interbreeding. We conducted a genome-wide association study (GWAS) of 15 traits including fibre quality, yield, disease resistance, maturity and plant architecture. The highest number of associated loci was for fibre quality, followed by disease resistance and yield. Using gene expression analyses and VIGS transgenic experiments, we confirmed the roles of five candidate genes regulating four key traits, that is disease resistance, fibre length, fibre strength and lint percentage. Geographical and temporal considerations demonstrated selection for the superior fibre quality (fibre length and fibre strength), and high lint percentage in improving G. barbadense in China. Pedigree selection breeding increased Fusarium wilt disease resistance and separately improved fibre quality and yield. Our work provides a foundation for understanding genomic variation and selective breeding of Sea Island cotton.
Fusarium wilt (FW) disease of cotton, caused by the fungus Fusarium oxysporum f. sp. vasinfectum (Fov), causes severe losses in cotton production worldwide. Though significant advancements have been made in development of FW‐resistant Upland cotton (Gossypium hirsutum) in resistance screening programs, the precise resistance genes and the corresponding molecular mechanisms for resistance to Fov remain unclear. Herein it is reported that Fov7, a gene unlike canonical plant disease‐resistance (R) genes, putatively encoding a GLUTAMATE RECEPTOR‐LIKE (GLR) protein, confers resistance to Fov race 7 in Upland cotton. A single nucleotide polymorphism (SNP) (C/A) in GhGLR4.8, resulting in an amino acid change (L/I), is associated with Fov resistance. A PCR‐based DNA marker (GhGLR4.8SNP(A/C)) is developed and shown to cosegregate with the Fov resistance. CRISPR/Cas9‐mediated knockout of Fov7 results in cotton lines extremely susceptible to Fov race 7 with a loss of the ability to induce calcium influx in response to total secreted proteins (SEPs) of Fov. Furthermore, coinfiltration of SEPs with GhGLR4.8A results in a hypersensitive response. This first report of a GLR‐encoding gene that functions as an R gene provides a new insight into plant–pathogen interactions and a new handle to develop cotton cultivars with resistance to Fov race 7.
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