Plants are susceptible to phytopathogens, including bacteria, fungi, and viruses, which cause colossal financial shortfalls (pre- and post-harvest) and threaten global food safety. To combat with these phytopathogens, plant possesses two-layer of defense in the form of PAMP-triggered immunity (PTI), or Effectors-triggered immunity (ETI). The understanding of plant-molecular interactions and revolution of high-throughput molecular techniques have opened the door for innovations in developing pathogen-resistant plants. In this context, Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-CRISPR-associated protein 9 (Cas9) has transformed genome editing (GE) technology and being harnessed for altering the traits. Here we have summarized the complexities of plant immune system and the use of CRISPR-Cas9 to edit the various components of plant immune system to acquire long-lasting resistance in plants against phytopathogens. This review also sheds the light on the limitations of CRISPR-Cas9 system, regulation of CRISPR-Cas9 edited crops and future prospective of this technology.

MADS-box family transcription factors play key roles in various developmental processes in plants. Here, we identified 108 MADS-box genes in the genome of chrysanthemum (Chrysanthemum nankingense). We classified these genes based on their phylogenetic relationships with MADS-box genes in Arabidopsis thaliana and lettuce (Lactuca sativa). Type I genes were subdivided into classes Mα (19 genes), Mβ (12 genes), and Mγ (10 genes), and type II genes were subdivided into classes MIKCC (64 genes) and MIKC* (3 genes). The MIKCC class genes were further divided into 16 subclasses that included genes described in the ABCDE flower development model. Each group of MADS-box genes showed a specific pattern of conserved protein motifs and exon-intron structure. We analyzed the expression levels of each MADS-box gene in root, stem, leaf, flower bud, disc floret, and ray floret tissues. Subfamilies AGL18, FLC, and SVP contained more members in chrysanthemum. The asterid-specific TM8 subfamily and eleven Asteraceae Specific-MADS CnMADS genes were present in chrysanthemum. Chrysanthemum is the lacking members of the AGL15 subfamily. Among the genes responsible for the ABCDE model, B-class genes were expanded in chrysanthemum with three AP3 and four PI genes. One AP3 homolog functions in marginal ray floret development, whereas the two other AP3 homologs function in the development of the central disc floret. Two of the four PI genes are expressed in chrysanthemum, specifically in both types of florets. The results of this study lay the foundation for further studies of the roles of MADS-box genes in flower development in chrysanthemum and of the evolution of MADS-box genes in plants.

Aster spathulifolius, a common ornamental and medicinal plant, is widely distributed in Korea and Japan, and is genetically classified into mainland and island types. Here, we sequenced the whole chloroplast genome of mainland A. spathulifolius and compared it with those of the island type and other Aster species. The chloroplast genome of mainland A. spathulifolius is 152,732 bp with a conserved quadripartite structure, has 37.28% guanine-cytosine (GC) content, and contains 114 non-redundant genes. Comparison of the chloroplast genomes between the two A. spathulifolius lines and the other Aster species revealed that their sequences, GC contents, gene contents and orders, and exon-intron structure were well conserved; however, differences were observed in their lengths, repeat sequences, and the contraction and expansion of the inverted repeats. The variations were mostly in the single-copy regions and non-coding regions, which, together with the detected simple sequence repeats, could be used for the development of molecular markers to distinguish between these plants. All Aster species clustered into a monophyletic group, but the chloroplast genome of mainland A. spathulifolius was more similar to the other Aster species than to that of the island A. spathulifolius. The accD and ndhF genes were detected to be under positive selection within the Aster lineage compared to other related taxa. The complete chloroplast genome of mainland A. spathulifolius presented in this study will be helpful for species identification and the analysis of the genetic diversity, evolution, and phylogenetic relationships in the Aster genus and the Asteraceae.

Key message Comparative transcriptome analysis of wild and cultivated chrysanthemums provides valuable genomic resources and helps uncover common and divergent patterns of genome and gene evolution in these species. Abstract Plants are unique in that they employ polyploidy (or whole-genome duplication, WGD) as a key process for speciation and evolution. The Chrysanthemum genus is closely associated with hybridization and polyploidization, with Chrysanthemum species exhibiting diverse ploidy levels. The commercially important species, C. morifolium is an allohexaploid plant that is thought to have originated via the hybridization of several Chrysanthemum species, but the genomic and molecular evolutionary mechanisms remain poorly understood. In the present study, we sequenced and compared the transcriptomes of C. morifolium and the wild Korean diploid species, C. boreale. De novo transcriptome assembly revealed 11,318 genes in C. morifolium and 10,961 genes in C. boreale, whose functions were annotated by homology searches. An analysis of synonymous substitution rates (Ks) of paralogous and orthologous genes suggested that the two Chrysanthemum species commonly experienced the Asteraceae paleopolyploidization and recent genome duplication or triplication before the divergence of these species. Intriguingly, C. boreale probably underwent rapid diploidization, with a reduction in chromosome number, whereas C. morifolium maintained the original chromosome number. Analysis of the ratios of non-synonymous to synonymous nucleotide substitutions (Ka/Ks) between orthologous gene pairs indicated that 107 genes experienced positive selection, which may have been crucial for the adaptation, domestication, and speciation of Chrysanthemum.

Wounds in tissues provide a pathway of entry for pathogenic fungi and bacteria in plants. Plants respond to wounding by regulating the expression of genes involved in their defense mechanisms. To analyze this response, we investigated the defense-related genes induced by wounding in the leaves of Senna tora using RNA sequencing. The genes involved in jasmonate and ethylene biosynthesis were strongly induced by wounding, as were a large number of genes encoding transcription factors such as ERFs, WRKYs, MYBs, bHLHs, and NACs. Wounding induced the expression of genes encoding pathogenesis-related (PR) proteins, such as PR-1, chitinase, thaumatin-like protein, cysteine proteinase inhibitor, PR-10, and plant defensin. Furthermore, wounding led to the induction of genes involved in flavonoid biosynthesis and the accumulation of kaempferol and quercetin in S. tora leaves. All these genes were expressed systemically in leaves distant from the wound site. These results demonstrate that mechanical wounding can lead to a systemic defense response in the Caesalpinioideae, a subfamily of the Leguminosae. In addition, a co-expression analysis of genes induced by wounding provides important information about the interactions between genes involved in plant defense responses.