In plants and animals, nucleotide-binding leucine-rich repeat (NLR) proteins are intracellular immune sensors that recognize and eliminate a wide range of invading pathogens. NLR-mediated immunity is known to be modulated by environmental factors. However, how pathogen recognition by NLRs is influenced by environmental factors such as light remains unclear. Here, we show that the agronomically important NLR Rpi-vnt1.1 requires light to confer disease resistance against races of the Irish potato famine pathogen Phytophthora infestans that secrete the effector protein AVRvnt1. The activation of Rpi-vnt1.1 requires a nuclear-encoded chloroplast protein, glycerate 3-kinase (GLYK), implicated in energy production. The pathogen effector AVRvnt1 binds the full-length chloroplast-targeted GLYK isoform leading to activation of Rpi-vnt1.1. In the dark, Rpi-vnt1.1–mediated resistance is compromised because plants produce a shorter GLYK—lacking the intact chloroplast transit peptide—that is not bound by AVRvnt1. The transition between full-length and shorter plant GLYK transcripts is controlled by a light-dependent alternative promoter selection mechanism. In plants that lack Rpi-vnt1.1, the presence of AVRvnt1 reduces GLYK accumulation in chloroplasts counteracting GLYK contribution to basal immunity. Our findings revealed that pathogen manipulation of chloroplast functions has resulted in a light-dependent immune response.

The beet armyworm, Spodoptera exigua (Hübner), is a worldwide, polyphagous agricultural pest feeding on vegetable, field, and flower crops. However, the lacking of genome architecture severely limits our understanding of its rapid adaptation and the development of efficient pest managements. We report a chromosome-level genome assembly using single-molecule real-time PacBio sequencing and Hi-C data. The final genome assembly was 446.80 Mb with a scaffold N50 of 14.36 Mb, and captured 97.9% complete arthropod Benchmarking Universal Single-Copy Orthologs (n=1,658). A total of 367 contigs were anchored to 32 pseudo-chromosomes, covering 96.18% (429.74 Mb) of the total genome length. We predicted 17,707 protein-coding genes, of which 81.69% were supported by transcriptome evidence and 97.94% matched the UniProt protein records. We also identified 867,102 (147.97 Mb/33.12%) repeats and 1,609 noncoding RNAs. Synteny analyses indicated a strong collinearity between three lepidopteran species. Our high-quality genome information provides a valuable resource for better understanding and management of the beet armyworm.

Filamentous plant pathogen genomes often display a bipartite architecture with gene sparse, repeat-rich compartments serving as a cradle for adaptive evolution. However, the extent to which this “two-speed” genome architecture is associated with genome-wide epigenetic modifications is unknown. Here, we show that the oomycete plant pathogens Phytophthora infestans and Phytophthora sojae possess functional adenine N6- methylation (6mA) methyltransferases that modulate patterns of 6mA marks across the genome. In contrast, 5-methylcytosine (5mC) could not be detected in the two Phytophthora species. Methylated DNA IP Sequencing (MeDIP-seq) of each species revealed that 6mA is depleted around the transcriptional starting sites (TSS) and is associated with low expressed genes, particularly transposable elements. Remarkably, genes occupying the gene-sparse regions have higher levels of 6mA compared to the remainder of both genomes, possibly implicating the methylome in adaptive evolution of Phytophthora. Among three putative adenine methyltransferases, DAMT1 and DAMT3 displayed robust enzymatic activities. Surprisingly, single knockouts of each of the 6mA methyltransferases in P. sojae significantly reduced in vivo 6mA levels, indicating that the three enzymes are not fully redundant. MeDIP-seq of the damt3 mutant revealed uneven patterns of 6mA methylation across genes, suggesting that PsDAMT3 may have a preference for gene body methylation after the TSS. Our findings provide evidence that 6mA modification is an epigenetic mark of Phytophthora genomes and that complex patterns of 6mA methylation by the expanded 6mA methyltransferases may be associated with adaptive evolution in these important plant pathogens.

ABSTRACT. In this study, inter-simple sequence repeats (ISSRs) and sequence-related amplified polymorphism (SRAP) were applied to assess the genetic diversity in 38 species of Chrysanthemum and related genera. A total of 204 and 567 bands were amplified by 24 ISSR and 25 SRAP primers, of which 196 (97%) and 557 (99%) were polymorphic, respectively. The ISSR-based genetic similarity ranged from 0.016 to 0.886 and averaged 0.201, while the SRAP-based genetic similarity varied from 0.010 to 0.811 and averaged 0.122. Both the ISSR and SRAP techniques revealed similar clustering patterns and grouped species of Chrysanthemum and Ajania together. The results of principal coordinate analysis corroborated the unweighted pair group method with arithmetic average clustering. Additionally, results from ISSR and SRAP data were significantly correlated (r = 0.89, P < 0.001). Knowledge about genetic diversity among species can aid the transfer of traits of interest from the wild into cultivated chrysanthemum in future distant interspecific breeding.

No abstract