A maize leucine-rich repeat receptor-like protein kinase mediates responses to fungal attack

Deciphering the complex roles of leucine-rich repeat receptor kinases (LRR-RKs) in plant signal transduction

Leucine-rich repeat receptor kinases (LRR-RKs) are essential receptor protein kinases in plants that are the key to signal perception and responses and central to regulating plant growth, development, and defense. Despite extensive research on the LRR-RK family, gaps persist in our understanding of their ligand recognition and activation mechanisms, interactions with co-receptor, signal transduction pathways, and biochemical and molecular regulation. Researchers have made significant advances in understanding the critical roles of LRR-RKs in plant growth and development, signal transduction, and stress responses. Here, we first summarized the gene expression levels of LRR-RKs in plants. We then reviewed the conservation and evolutionary relationships of these genes across different species. We also investigated the molecular mechanisms underlying the variations in LRR-RK signaling under different environmental conditions. Finally, we provide a comprehensive summary of how abiotic and biotic stresses modulate LRR-RK signaling pathways in plants.

Exploring the genomic landscape of gummy stem blight resistance in watermelon through QTL-Seq

BACKGROUND

Watermelon is a nutritionally and economically significant crop in the US and globally. Gummy Stem Blight (GSB), caused by three cryptic Stagonosporopsis species, is one of the most devastating diseases affecting watermelon in the US, impacting most of the plant's above-ground parts. This study aimed to identify key Quantitative Trait Variants (QTVs) that include SNPs and In/Dels associated with GSB resistance in selfed derivatives of advanced multicross interspecific derivatives population derived from intercrosses between the most resistant lines of Citrullus amarus and highly susceptible cultivars of Citrullus lanatus.

RESULTS

Resistant and susceptible bulks were created by combining equimolar DNA concentrations from 30 extremely resistant derivatives and 30 extremely susceptible lines. These bulks underwent whole-genome sequencing, generating over 1 billion reads per bulk to achieve comprehensive genome coverage. The mapping percentage of the bulks to the parental genomes ranged from 92 to 99%. More than 6 million SNPs and 1 million indels were identified from the resistant parental genome, compared to fewer than 2 million SNPs and 0.4 million indels from the susceptible parental genome. QTNs associated with GSB resistance were identified using single-nucleotide polymorphism-index and Gprime methods. Statistically significant variants/loci linked to GSB resistance were found on chromosomes 1, 2, 3, 5, 7, 10, and 11. Notably, the genes Lipase class 3 family protein, Ribosome hibernation promotion factor (CaU02G00010), Ubiquitin-like-specific protease 1D (CaU03G04260), and Zinc finger CCCH domain-containing 15 (CaU03G10970) harbored the highest delta SNPs. Several previously published genes, including Avr9/Cf-9 Rapidly Elicited Protein (CaU07G12990) on chromosome 7, were also identified.

CONCLUSIONS

Identifying significant loci associated with GSB resistance has facilitated the development of PACE assays, which will aid in breeding GSB-resistant watermelon cultivars. These findings provide critical insights into the genetic basis of GSB resistance and represent a significant step towards improving the resilience of watermelon crops against this devastating disease.

Phylogeny of the plant receptor-like kinase (RLK) gene family and expression analysis of wheat RLK genes in response to biotic and abiotic stresses

BACKGROUND

The receptor-like kinase (RLK) gene families in plants contains a large number of members. They are membrane proteins with an extracellular receptor domain and participate in biotic and abiotic stress responses.

RESULTS

In this study, we identified RLKs in 15 representative plant genomes, including wheat, and classified them into 64 subfamilies by using four types of phylogenetic trees and HMM models. Conserved exon‒intron structures with conserved exon phases in the kinase domain were found in many RLK subfamilies from Physcomitrella patens to Triticum aestivum. Domain distributions of RLKs were also diagrammed. Collinearity events and tandem gene clusters suggested that polyploidization and tandem duplication events contributed to the member expansions of T. aestivum RLKs. Global expression pattern analysis was performed by using public transcriptome data. These analyses were involved in T. aestivum, Aegilops tauschii and Brachypodium distachyon RLKs under biotic and abiotic stresses. We also selected 9 RLKs to validate the transcriptome prediction by using qRT‒PCR under drought treatment and with Fusarium graminearum infection. The expression trends of these 9 wheat RLKs from public transcriptome data were consistent with the results of qRT‒PCR, indicating that they might be stress response genes under drought or F. graminearum treatments.

CONCLUSION

In this study, we identified, classified, evolved, and expressed RLKs in wheat and related plants. Thus, our results will provide insights into the evolutionary history and molecular mechanisms of wheat RLKs.

Comparative transcriptome meta-analysis reveals a set of genes involved in the responses to multiple pathogens in maize

Maize production is constantly threatened by the presence of different fungal pathogens worldwide. Genetic resistance is the most favorable approach to reducing yield losses resulted from fungal diseases. The molecular mechanism underlying disease resistance in maize remains largely unknown. The objective of this study was to identify key genes/pathways that are consistently associated with multiple fungal pathogen infections in maize. Here, we conducted a meta-analysis of gene expression profiles from seven publicly available RNA-seq datasets of different fungal pathogen infections in maize. We identified 267 common differentially expressed genes (co-DEGs) in the four maize leaf infection experiments and 115 co-DEGs in all the seven experiments. Functional enrichment analysis showed that the co-DEGs were mainly involved in the biosynthesis of diterpenoid and phenylpropanoid. Further investigation revealed a set of genes associated with terpenoid phytoalexin and lignin biosynthesis, as well as potential pattern recognition receptors and nutrient transporter genes, which were consistently up-regulated after inoculation with different pathogens. In addition, we constructed a weighted gene co-expression network and identified several hub genes encoding transcription factors and protein kinases. Our results provide valuable insights into the pathways and genes influenced by different fungal pathogens, which might facilitate mining multiple disease resistance genes in maize.

The moss-specific transcription factor PpERF24 positively modulates immunity against fungal pathogens in Physcomitrium patens

APETALA2/ethylene response factors (AP2/ERFs) transcription factors (TFs) have greatly expanded in land plants compared to algae. In angiosperms, AP2/ERFs play important regulatory functions in plant defenses against pathogens and abiotic stress by controlling the expression of target genes. In the moss Physcomitrium patens, a high number of members of the ERF family are induced during pathogen infection, suggesting that they are important regulators in bryophyte immunity. In the current study, we analyzed a P. patens pathogen-inducible ERF family member designated as PpERF24. Orthologs of PpERF24 were only found in other mosses, while they were absent in the bryophytes Marchantia polymorpha and Anthoceros agrestis, the vascular plant Selaginella moellendorffii, and angiosperms. We show that PpERF24 belongs to a moss-specific clade with distinctive amino acids features in the AP2 domain that binds to the DNA. Interestingly, all P. patens members of the PpERF24 subclade are induced by fungal pathogens. The function of PpERF24 during plant immunity was assessed by an overexpression approach and transcriptomic analysis. Overexpressing lines showed increased defenses to infection by the fungal pathogens Botrytis cinerea and Colletotrichum gloeosporioides evidenced by reduced cellular damage and fungal biomass compared to wild-type plants. Transcriptomic and RT-qPCR analysis revealed that PpERF24 positively regulates the expression levels of defense genes involved in transcriptional regulation, phenylpropanoid and jasmonate pathways, oxidative burst and pathogenesis-related (PR) genes. These findings give novel insights into potential mechanism by which PpERF24 increases plant defenses against several pathogens by regulating important players in plant immunity.