The Gain-of-Function Mutation, OsSpl26, Positively Regulates Plant Immunity in Rice

Restriction site-associated DNA sequencing (RAD-seq) of tea plant (Camellia sinensis) in Sichuan province, China, provides insights into free amino acid and polyphenol contents of tea

Worldwide, tea is a popular beverage; within the realm of Chinese tea, Sichuan tea holds particular significance for its role in the origin and composition of Chinese tea cultivars. Sichuan tea is noted for its rich content of free amino acids (FAAs) and tea polyphenols (TPs), which has made it an important subject for studying genetic diversity and the genes regulating these compounds. In this study, 139 varieties of tea were collected from areas in Sichuan Province, China, with similar geographical and climatic conditions. The FAA content was approximately 3% and the TP content was approximately 17%. Using RAD sequencing, 5,656,224 variant loci were identified, primarily comprising SNPs (94.17%) and indels (5.83%). Evolutionary analysis revealed that genetic divergence was not closely linked to the collection location. Population structure analysis confirmed a division into two main populations having a similar composition to the phylogenetic clusters. Screening for FAA-related SNPs identified significant loci associated with 33 genes that potentially regulate FAA content. Similarly, TP-related analysis pinpointed 8 SNPs significantly linked to 20 candidate genes. Notably, genetic associations hinted at the genes involved in the stress response and the accumulation of phenolic compounds, enhancing the understanding of determinants of tea quality. This research underscores the potential for molecular breeding based on genetic insights, suggesting pathways to improve the FAA and TP contents in tea. These findings not only provide a solid foundation for exploring gene-chemical interactions but also offer practical strategies for improving the nutritional and sensory attributes of tea cultivars through informed breeding practices.

A Novel Single Base Mutation in OsSPL42 Leads to the Formation of Leaf Lesions in Rice

Rice spotted-leaf mutants serve as valuable resources for studying plant programmed cell death (PCD) and disease resistance mechanisms, making them crucial for research on disease resistance in rice. Map-based cloning was used to identify and clone the spotted-leaf gene OsSPL42. Then, functional complementation and CRISPR/Cas9 techniques were also employed to further validate the function of this gene. By applying leaf clippings for bacterial blight (BB) inoculation, the BB resistance of different rice lines was assessed. The results in this study were as follows: The OsSPL42 behaved as a recessive nuclear gene and was narrowed down to a 111 kb region on chromosome 8. All T0 transgenic rice plants in the complementation experiments exhibited a wild-type phenotype, without any lesion spots on the rice leaves. This suggests that the LOC_Os08g06100 encoding O-methyltransferase is the candidate gene for the mutant spl42. The OsSpl42 is widely expressed and the OsSPL42-GFP protein is mainly localized in the cytoplasm. OsSPL42 overexpression lines are more susceptible to BBs, which indicates that OsSPL42 may act as a negative regulator of rice resistance to BB. In summary, we speculate that OsSPL42 plays an important role in the regulation of pathogen response, providing new insights into plant defense mechanisms.

CRISPR-Cas9 and beyond: identifying target genes for developing disease-resistant plants

Throughout the history of crop domestication, desirable traits have been selected in agricultural products. However, such selection often leads to crops and vegetables with weaker vitality and viability than their wild ancestors when exposed to adverse environmental conditions. Considering the increasing human population and climate change challenges, it is crucial to enhance crop quality and quantity. Accordingly, the identification and utilization of diverse genetic resources are imperative for developing disease-resistant plants that can withstand unexpected epidemics of plant diseases. In this review, we provide a brief overview of recent progress in genome-editing technologies, including zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein 9 (Cas9) technologies. In particular, we classify disease-resistant mutants of Arabidopsis thaliana and several crop plants based on the roles or functions of the mutated genes in plant immunity and suggest potential target genes for molecular breeding of genome-edited disease-resistant plants. Genome-editing technologies are resilient tools for sustainable development and promising solutions for coping with climate change and population increases.

Development of activation-tagged gain-of-functional mutants in indica rice line (BPT 5204) for sheath blight resistance

BACKGROUND

The development of sheath blight (ShB) resistance varieties has been a challenge for scientists for long time in rice. Activation tagging is an efficient gain-of-function mutation approach to create novel phenotypes and to identify their underlying genes. In this study, a mutant population was developed employing activation tagging in the recalcitrant indica rice (Oryza sativa L.) cv. BPT 5204 (Samba Mahsuri) through activation tagging.

METHODS AND RESULTS

In this study, we have generated more than 1000 activation tagged lines in indica rice, from these mutant population 38 (GFP- RFP+) stable Ds plants were generated through germinal transposition at T2 generation based on molecular analysis and seeds selected on hygromycin (50 mg/L) containing medium segregation analyses confirmed that the transgene inherited as mendelian segregation ratio of 3:1 (3 resistant: 1 susceptible). Of them, five stable activation tagged Ds lines (M-Ds-1, M-Ds-2, M-Ds-3, M-Ds-4 and M-Ds-5) were selected based on phenotypic observation through screening for sheath blight (ShB) resistance caused by fungal pathogen Rhizoctonia solani (R. solani),. Among them, M-Ds-3 and M-Ds-5 lines showed significant resistance for ShB over other tagged lines and wild type (WT) plants. Furthermore, analysed for launch pad insertion through TAIL-PCR results and mapped on corresponding rice chromosomes. Flanking sequence and gene expression analysis revealed that the upregulation of glycoside hydrolase-OsGH or similar to Class III chitinase homologue (LOC_Os08g40680) in M-Ds-3 and a hypothetical protein gene (LOC_Os01g55000) in M-Ds-5 are potential candidate genes for sheath blight resistance in rice.

CONCLUSION

In the present study, we developed Ac-Ds based ShB resistance gain-of-functional mutants through activation tagging in rice. These activation tagged mutant lines can be excellent sources for the development of ShB resistant cultivars in rice.

Fine-mapping of a major locus for Fusarium wilt resistance in flax (Linum usitatissimum L.)

KEY MESSAGE

Fine-mapping of a locus on chromosome 1 of flax identified an S-lectin receptor-like kinase (SRLK) as the most likely candidate for a major Fusarium wilt resistance gene. Fusarium wilt, caused by the soil-borne fungal pathogen Fusarium oxysporum f. sp. lini, is a devastating disease in flax. Genetic resistance can counteract this disease and limit its spread. To map major genes for Fusarium wilt resistance, a recombinant inbred line population of more than 700 individuals derived from a cross between resistant cultivar 'Bison' and susceptible cultivar 'Novelty' was phenotyped in Fusarium wilt nurseries at two sites for two and three years, respectively. The population was genotyped with 4487 single nucleotide polymorphism (SNP) markers. Twenty-four QTLs were identified with IciMapping, 18 quantitative trait nucleotides with 3VmrMLM and 108 linkage disequilibrium blocks with RTM-GWAS. All models identified a major QTL on chromosome 1 that explained 20-48% of the genetic variance for Fusarium wilt resistance. The locus was estimated to span ~ 867 Kb but included a ~ 400 Kb unresolved region. Whole-genome sequencing of 'CDC Bethune', 'Bison' and 'Novelty' produced ~ 450 Kb continuous sequences of the locus. Annotation revealed 110 genes, of which six were considered candidate genes. Fine-mapping with 12 SNPs and 15 Kompetitive allele-specific PCR (KASP) markers narrowed down the interval to ~ 69 Kb, which comprised the candidate genes Lus10025882 and Lus10025891. The latter, a G-type S-lectin receptor-like kinase (SRLK) is the most likely resistance gene because it is the only polymorphic one. In addition, Fusarium wilt resistance genes previously isolated in tomato and Arabidopsis belonged to the SRLK class. The robust KASP markers can be used in marker-assisted breeding to select for this major Fusarium wilt resistance locus.