Two Different Transcripts of a LAMMER Kinase Gene Play Opposite Roles in Disease Resistance

Genome-Wide Association Studies on Chinese Wheat Cultivars Reveal a Novel Fusarium Crown Rot Resistance Quantitative Trait Locus on Chromosome 3BL

Fusarium crown rot (FCR), primarily caused by Fusarium pseudograminearum, has emerged as a new threat to wheat production and quality in North China. Genetic enhancement of wheat resistance to FCR remains the most effective approach for disease control. In this study, we phenotyped 435 Chinese wheat cultivars through FCR inoculation at the seedling stage in a greenhouse. Our findings revealed that only approximately 10.8% of the wheat germplasms displayed moderate or high resistance to FCR. A genome-wide association study (GWAS) using high-density 660K SNP led to the discovery of a novel quantitative trait locus on the long arm of chromosome 3B, designated as Qfcr.hebau-3BL. A total of 12 significantly associated SNPs were closely clustered within a 1.05 Mb physical interval. SNP-based molecular markers were developed to facilitate the practical application of Qfcr.hebau-3BL. Among the five candidate FCR resistance genes within the Qfcr.hebau-3BL, we focused on TraesCS3B02G307700, which encodes a protein kinase, due to its expression pattern. Functional validation revealed two transcripts, TaSTK1.1 and TaSTK1.2, with opposing roles in plant resistance to fungal disease. These findings provide insights into the genetic basis of FCR resistance in wheat and offer valuable resources for breeding resistant varieties.

Full-length transcriptome reconstruction reveals genetic differences in hybrids of Oryza sativa and Oryza punctata with different ploidy and genome compositions

BACKGROUND

Allopolyploid breeding is an efficient technique for improving the low seed setting rate of autotetraploids in plant breeding and one of the most promising breeding methods. However, there have been few comprehensive studies of the posttranscriptional mechanism in allopolyploids.

RESULTS

By crossing cultivated rice (Oryza sativa, genome AA) with wild rice (Oryza punctata, genome BB), we created hybrid rice lines with different ploidy and genome compositions [diploid hybrid F01 (AB), allotetraploid hybrid F02 (AABB) and F03 (AAAB)]. The genetic differences of the hybrids and the mechanism of allopolyploid breeding dominance were revealed through morphological and cytological observations and single molecule real-time sequencing techniques. The tissues and organs of allotetraploid hybrid F02 exhibited "gigantism" and the highest levels of fertility. The numbers of non-redundant transcripts, gene loci and new isoforms in the polyploid rice lines were higher and the isoform lengths greater than those of the diploid line. Moreover, alternative splicing (AS) events occurred twice as often in the polyploid rice lines than the diploid line. During these events, intron retention dominated. Furthermore, a large number of new genes and isoforms specific to the lines of different ploidy were discovered.

CONCLUSIONS

The results indicated that alternative polyadenylation (APA) and AS events contributed to the complexity and superiority of polyploids in the activity of translation regulators, nucleic acid binding transcription factor activities and the regulation of molecular function. Therefore, these APA and AS events in allopolyploid rice were found to play a role in regulation. Our study provides new germplasm for polyploid rice breeding and reveals complex regulatory mechanisms that may be related to heterosis and fertility.

Stress-Induced Changes in Alternative Splicing Landscape in Rice: Functional Significance of Splice Isoforms in Stress Tolerance

Improvements in yield and quality of rice are crucial for global food security. However, global rice production is substantially hindered by various biotic and abiotic stresses. Making further improvements in rice yield is a major challenge to the rice research community, which can be accomplished through developing abiotic stress-resilient rice varieties and engineering durable agrochemical-independent pathogen resistance in high-yielding elite rice varieties. This, in turn, needs increased understanding of the mechanisms by which stresses affect rice growth and development. Alternative splicing (AS), a post-transcriptional gene regulatory mechanism, allows rapid changes in the transcriptome and can generate novel regulatory mechanisms to confer plasticity to plant growth and development. Mounting evidence indicates that AS has a prominent role in regulating rice growth and development under stress conditions. Several regulatory and structural genes and splicing factors of rice undergo different types of stress-induced AS events, and the functional significance of some of them in stress tolerance has been defined. Both rice and its pathogens use this complex regulatory mechanism to devise strategies against each other. This review covers the current understanding and evidence for the involvement of AS in biotic and abiotic stress-responsive genes, and its relevance to rice growth and development. Furthermore, we discuss implications of AS for the virulence of different rice pathogens and highlight the areas of further research and potential future avenues to develop climate-smart and disease-resistant rice varieties.

Alternative splicing and its regulatory role in woody plants

Alternative splicing (AS) is an important post-transcriptional process to enhance proteome diversity in eukaryotic organisms. In plants, numerous reports have primarily focused on AS analysis in model plant species or herbaceous plants, leading to a notable lack of research on AS in woody plants. More importantly, emerging evidence indicates that many important traits, including wood formation and stress resistance, in woody plants are controlled by AS. In this review article, we summarize the current progress of all kinds of AS studies in different tree species at various stages of development and in response to various stresses, revealing the significant role played by AS in woody plants, as well as the similar properties and differential regulation within their herbaceous counterparts. Furthermore, we propose several potential strategies to facilitate the functional characterization of splicing factors in woody plants and evaluate a general pipeline for the systematic characterization of splicing isoforms in a complex AS regulatory network. The utilization of genetic studies and high-throughput omics integration approaches to analyze AS genes and splicing factors is likely to further advance our understanding of AS modulation in woody plants.

Full-Length Transcript-Based Proteogenomics of Rice Improves Its Genome and Proteome Annotation

Rice (Oryza sativa) molecular breeding has gained considerable attention in recent years, but inaccurate genome annotation hampers its progress and functional studies of the rice genome. In this study, we applied single-molecule long-read RNA sequencing (lrRNA_seq)-based proteogenomics to reveal the complexity of the rice transcriptome and its coding abilities. Surprisingly, approximately 60% of loci identified by lrRNA_seq are associated with natural antisense transcripts (NATs). The high-density genomic arrangement of NAT genes suggests their potential roles in the multifaceted control of gene expression. In addition, a large number of fusion and intergenic transcripts have been observed. Furthermore, 906,456 transcript isoforms were identified, and 72.9% of the genes can generate splicing isoforms. A total of 706,075 posttranscriptional events were subsequently categorized into 10 subtypes, demonstrating the interdependence of posttranscriptional mechanisms that contribute to transcriptome diversity. Parallel short-read RNA sequencing indicated that lrRNA_seq has a superior capacity for the identification of longer transcripts. In addition, over 190,000 unique peptides belonging to 9,706 proteoforms/protein groups were identified, expanding the diversity of the rice proteome. Our findings indicate that the genome organization, transcriptome diversity, and coding potential of the rice transcriptome are far more complex than previously anticipated.

The complexity of alternative splicing and landscape of tissue-specific expression in lotus (Nelumbo nucifera) unveiled by Illumina- and single-molecule real-time-based RNA-sequencing

Alternative splicing (AS) plays a critical role in regulating different physiological and developmental processes in eukaryotes, by dramatically increasing the diversity of the transcriptome and the proteome. However, the saturation and complexity of AS remain unclear in lotus due to its limitation of rare obtainment of full-length multiple-splice isoforms. In this study, we apply a hybrid assembly strategy by combining single-molecule real-time sequencing and Illumina RNA-seq to get a comprehensive insight into the lotus transcriptomic landscape. We identified 211,802 high-quality full-length non-chimeric reads, with 192,690 non-redundant isoforms, and updated the lotus reference gene model. Moreover, our analysis identified a total of 104,288 AS events from 16,543 genes, with alternative 3ʹ splice-site being the predominant model, following by intron retention. By exploring tissue datasets, 370 tissue-specific AS events were identified among 12 tissues. Both the tissue-specific genes and isoforms might play important roles in tissue or organ development, and are suitable for ‘ABCE’ model partly in floral tissues. A large number of AS events and isoform variants identified in our study enhance the understanding of transcriptional diversity in lotus, and provide valuable resource for further functional genomic studies.

The Dual-Specificity LAMMER Kinase Affects Stress-Response and Morphological Plasticity in Fungi

The morphological plasticity of fungal pathogens has long been implicated in their virulence and is often influenced by extracellular factors. Complex signal transduction cascades are critical for sensing stresses imposed by external cues such as antifungal drugs, and for mediating appropriate cellular responses. Many of these signal transduction cascades are well-conserved and involve in the distinct morphogenetic processes during the life cycle of the pathogenic fungi. The dual-specificity LAMMER kinases are evolutionarily conserved across species ranging from yeasts to mammals and have multiple functions in various physiological processes; however, their functions in fungi are relatively unknown. In this review, we first describe the involvement of LAMMER kinases in cell surface changes, which often accompany alterations in growth pattern and differentiation. Then, we focus on the LAMMER kinase-dependent molecular machinery responsible for the stress responses and cell cycle regulation. Last, we discuss the possible cross-talk between LAMMER kinases and other signaling cascades, which integrates exogenous and host signals together with genetic factors to affect the morphological plasticity and virulence in fungi.

A malectin-like/leucine-rich repeat receptor protein kinase gene, RLK-V, regulates powdery mildew resistance in wheat

Pattern recognition receptors (PRRs) can trigger plant immunity through the recognition of pathogen-associated molecular patterns. In this study, we report that a malectin-like/leucine-rich repeat receptor protein kinase gene, RLK-V, from Haynaldia villosa putatively acts as a PRR to positively regulate powdery mildew resistance caused by Blumeria graminis f. sp. tritici (Bgt) in wheat. RLK-V has two alternatively spliced transcripts corresponding to an intact RLK-V1.1 and a truncated RLK-V1.2 caused by intron retention. Expression analysis showed that both transcripts could be up-regulated by Bgt in resistant materials, whereas the functional RLK-V1.1 was expressed only after Bgt inoculation. Promoter activity assays indicated that RLK-V could respond to Bgt even in susceptible wheat. Silencing of RLK-V in Pm21-carrying resistant materials resulted in compromised resistance to Bgt. In addition, over-expression of RLK-V1.1 in Pm21-lacking susceptible Yangmai158 and SM-1 by single-cell transient expression and stable transformation in Yangmai158 could improve powdery mildew resistance. We propose that RLK-V regulates basal resistance to powdery mildew, which is also required for broad-spectrum resistance mediated by the Pm21 gene. Over-expression of RLK-V1.1 could trigger cell death in Nicotiana benthamiana, and RLK-V1.1 transgenic wheat accumulated more reactive oxygen species and displayed a stronger hypersensitive response than did the recipient, which led to enhanced Bgt resistance. However, constitutive activation of RLK-V1.1 resulted in the abnormal growth of transgenic plants.

A global survey of alternative splicing in allopolyploid cotton: landscape, complexity and regulation

Alternative splicing (AS) is a crucial regulatory mechanism in eukaryotes, which acts by greatly increasing transcriptome diversity. The extent and complexity of AS has been revealed in model plants using high-throughput next-generation sequencing. However, this technique is less effective in accurately identifying transcript isoforms in polyploid species because of the high sequence similarity between coexisting subgenomes. Here we characterize AS in the polyploid species cotton. Using Pacific Biosciences single-molecule long-read isoform sequencing (Iso-Seq), we developed an integrated pipeline for Iso-Seq transcriptome data analysis (https://github.com/Nextomics/pipeline-for-isoseq). We identified 176 849 full-length transcript isoforms from 44 968 gene models and updated gene annotation. These data led us to identify 15 102 fibre-specific AS events and estimate that c. 51.4% of homoeologous genes produce divergent isoforms in each subgenome. We reveal that AS allows differential regulation of the same gene by miRNAs at the isoform level. We also show that nucleosome occupancy and DNA methylation play a role in defining exons at the chromatin level. This study provides new insights into the complexity and regulation of AS, and will enhance our understanding of AS in polyploid species. Our methodology for Iso-Seq data analysis will be a useful reference for the study of AS in other species.