Blast, caused by Magnaporthe oryzae, is one of the most destructive diseases affecting rice production. Understanding population dynamics of the pathogen’s avirulence genes is pre-required for breeding and then deploying new cultivars carrying promising resistance genes. The divergence and population structure of AvrPii was dissected in the populations of southern (Guangdong, Hunan, and Guizhou) and northern (Jilin, Liaoning, and Heilongjiang) China, via population genetic and evolutionary approaches. The evolutionary divergence between a known haplotype AvrPii-J and a novel one AvrPii-C was demonstrated by haplotype-specific amplicon-based sequencing and genetic transformation. The different avirulent performances of a set of seven haplotype-chimeric mutants suggested that the integrity of the full-length gene structures is crucial to express functionality of individual haplotypes. All the four combinations of phenotypes/genotypes were detected in the three southern populations, and only two in the northern three, suggesting that genic diversity in the southern region was higher than those in the northern one. The population structure of the AvrPii family was shaped by balancing, purifying, and positive selection pressures in the Chinese populations. The AvrPii-J was recognized as the wild type that emerged before rice domestication. Considering higher frequencies of avirulent isolates were detected in Hunan, Guizhou, and Liaoning, the cognate resistance gene Pii could be continuously used as a basic and critical resistance resource in such regions. The unique population structures of the AvrPii family found in China have significant implications for understanding how the AvrPii family has kept an artful balance and purity among its members (haplotypes) those keenly interact with Pii under gene-for-gene relationships. The lesson learned from case studies on the AvrPii family is that much attention should be paid to haplotype divergence of target gene.

Blast, caused by Magnaporthe oryzae, is one of the most destructive diseases affecting rice production. Understanding population dynamics of the pathogen avirulence genes is pre-required for breeding and then deploying new cultivars carrying promising resistance genes. The divergence and population structure of AvrPii was dissected in the populations of southern (Guangdong, Hunan, and Guizhou) and northern (Jilin, Liaoning, and Heilongjiang) China, via population genetic and evolutionary approaches. The evolutionary divergence between a known haplotype AvrPii-J and a novel one AvrPii-C was demonstrated by haplotype-specific amplicon-based sequencing and genetic transformation. The different avirulent performances of a set of seven haplotype-chimeric mutants suggested that the integrity of the full-length gene structures is crucial to express functionality of individual haplotypes. The population structure of the AvrPii family was shaped by balancing, purifying, and positive selection pressures in the Chinese populations. The AvrPii-J was recognized as the wild type that emerged before rice domestication. Considering higher frequencies of avirulent isolates were detected in Hunan, Guizhou, and Liaoning, the cognate resistance gene Pii could be continuously served as a basic and critical resistance resource in such regions. The unique population structures of the AvrPii family found in China have significant implications for understanding how the AvrPii family has kept an artful balance and purify among its members (haplotypes) those keenly interact with the cognate resistance gene under gene-for-gene relationships.

Background/Objectives: Kernel dehydration is an important agronomic trait influencing mechanical harvesting efficiency, post-harvest drying costs, and grain storage quality in maize (Zea mays L.). Although the genetic and molecular basis of whole-kernel dehydration has been increasingly investigated, tissue-specific physiological and molecular patterns, particularly those associated with the embryo, remain insufficiently characterized. In this study, four maize inbred lines with contrasting dehydration capacities were selected to characterize tissue-specific dehydration dynamics and associated molecular patterns. Methods: Moisture content and dehydration rates of kernels, endosperms, and embryos were monitored from 10 to 55 days after pollination (DAP), followed by correlation analyses with kernel- and ear-related agronomic traits. Transcriptome sequencing, weighted gene co-expression network analysis (WGCNA), and untargeted metabolomics were integrated to characterize molecular processes associated with contrasting embryo dehydration phenotypes. Results: Embryo dehydration closely paralleled whole-kernel dehydration, and embryo dehydration rate was strongly associated with kernel dehydration rate. Transcriptomic and WGCNA analyses revealed developmental- and genotype-dependent expression changes, particularly during late maturation, and identified dehydration-associated modules enriched in lipid metabolism, glycolysis, hormone signaling, and stress-responsive processes, including fatty acid metabolism, ABA- and ethylene-related signaling, and MAPK-related genes. FDR-controlled metabolomics further revealed genotype- and developmental-stage-dependent metabolite differences associated with organic acid metabolism, amino acid metabolism, transport-associated processes, and secondary metabolism. Pathway-level integration highlighted ABA- and ethylene-associated candidate processes associated with variation in embryo dehydration. Conclusions: Collectively, these findings provide an embryo-focused characterization of physiological and multi-omics variation associated with maize kernel dehydration and identify candidate molecular processes for further functional investigation. Further validation across broader germplasm panels, environmental conditions, and experimental systems will be required to determine the causal roles and potential breeding relevance of these candidate processes.