Genetic and Molecular Characterization of a Self-Compatible Brassica rapa Line Possessing a New Class II S Haplotype

Most flowering plants have evolved a self-incompatibility (SI) system to maintain genetic diversity by preventing self-pollination. The Brassica species possesses sporophytic self-incompatibility (SSI), which is controlled by the pollen- and stigma-determinant factors SP11/SCR and SRK. However, the mysterious molecular mechanism of SI remains largely unknown. Here, a new class II S haplotype, named BrS-325, was identified in a pak choi line ‘325’, which was responsible for the completely self-compatible phenotype. To obtain the entire S locus sequences, a complete pak choi genome was gained through Nanopore sequencing and de novo assembly, which provided a good reference genome for breeding and molecular research in B. rapa. S locus comparative analysis showed that the closest relatives to BrS-325 was BrS-60, and high sequence polymorphism existed in the S locus. Meanwhile, two duplicated SRKs (BrSRK-325a and BrSRK-325b) were distributed in the BrS-325 locus with opposite transcription directions. BrSRK-325b and BrSCR-325 were expressed normally at the transcriptional level. The multiple sequence alignment of SCRs and SRKs in class II S haplotypes showed that a number of amino acid variations were present in the contact regions (CR II and CR III) of BrSCR-325 and the hypervariable regions (HV I and HV II) of BrSRK-325s, which may influence the binding and interaction between the ligand and the receptor. Thus, these results suggested that amino acid variations in contact sites may lead to the SI destruction of a new class II S haplotype BrS-325 in B. rapa. The complete SC phenotype of ‘325’ showed the potential for practical breeding application value in B. rapa.

Characterization of a Common S Haplotype BnS-6 in the Self-Incompatibility of Brassica napus

Self-incompatibility (SI) is a pollen-stigma recognition system controlled by a single and highly polymorphic genetic locus known as the S-locus. The S-locus exists in all Brassica napus (B. napus, AACC), but natural B. napus accessions are self-compatible. About 100 and 50 S haplotypes exist in Brassica rapa (AA) and Brassica oleracea (CC), respectively. However, S haplotypes have not been detected in B. napus populations. In this study, we detected the S haplotype distribution in B. napus and ascertained the function of a common S haplotype BnS-6 through genetic transformation. BnS-1/BnS-6 and BnS-7/BnS-6 were the main S haplotypes in 523 B. napus cultivars and inbred lines. The expression of SRK in different S haplotypes was normal (the expression of SCR in the A subgenome affected the SI phenotype) while the expression of BnSCR-6 in the C subgenome had no correlation with the SI phenotype in B. napus. The BnSCR-6 protein in BnSCR-6 overexpressed lines was functional, but the self-compatibility of overexpressed lines did not change. The low expression of BnSCR-6 could be a reason for the inactivation of BnS-6 in the SI response of B. napus. This study lays a foundation for research on the self-compatibility mechanism and the SI-related breeding in B. napus.

Evaluation of resistance to pyrethroid and organophosphate adulticides, and kdr genotyping in Ades aegypti populations from Roraima, the Northernmost Brazilian State

Background Roraima is the northernmost State in Brazil and makes international borders with Venezuela and Guyana. Although mostly covered by the tropical forests, the urban centers are highly infested with Ae. aegypti and endemic for dengue, Zika and chikungunya. Here we presented the levels of Ae. aegypti infestation and number of arboviruses cases between 2015 and 2018 in the studied localities. We evaluated the insecticide resistance status of Ae. aegypti populations from the capital Boa Vista, two cities in international borders: Pacaraima and Bonfim, and Rorainópolis in the limit with Amazonas State, collected in 2016 and 2018. Methods WHO like tube tests with the pyrethroid deltamethrin (0.05 and 0.12%) and the organophosphate malathion (0.7%) were conducted. Genotyping of kdr mutations, related to resistance to pyrethroids, were performed for the SNP variations in the sites 1016 and 1534 of the voltage gated sodium channel gene (Na V ) with a TaqMan qPCR approach. Results Only Ae. aegypti was present in our collection, meaning that there is still a barrier that Ae. albopictus was still not able to transpose from Amazonas toward Roraima. All Ae. aegypti populations were susceptible to 0.7% malathion in 2016, however mortality dropped to under 90% in Bonfim and Pacaraima in 2018. All populations were resistant to 0.5% deltamethrin in both years. The time that 50% of females suffered knockdown ( Kd T 50 ) under exposition to 0.5% deltamethrin was 3.3-5.9 fold longer in mosquitoes from the populations compared to Rockefeller. Only Pacaraima (2018) remained resistant to 0.12% deltamethrin. The kdr genotyping revealed the absence of the wild-type Na V S haplotype (1016Val + 1534Phe) in populations from Roraima, meaning that all tested individuals had a genetic background for resistance to pyrethroid. The double kdr Na V R2 haplotype (1016Ile + 15434Cys) was under higher frequencies in all populations except Rorainópolis, where this haplotype seems to have arrived recently. Conclusions These results are important to the knowledge about insecticide resistance status of Ae. aegypti populations from Roraima and will help to improve vector control strategies that may be applied to diverse localities with similar conditions.

High temperature causes breakdown of S haplotype-dependent stigmatic self-incompatibility in self-incompatible Arabidopsis thaliana

High temperature disrupts the targeting of SRK to the plasma membrane, resulting in breakdown of the stigmatic self-incompatibility response in self-incompatible Arabidopsis transformants.

Cross-incompatibility and self-incompatibility: unrelated phenomena in wild and cultivated potatoes?

Knowledge of internal hybridization barriers is relevant for germplasm conservation and utilization. The two pre-zygotic barriers are pollen–pistil self-incompatibility (SI) and cross-incompatibility (CI). To ascertain whether SI and CI were phenotypically related phenomena in potatoes, extensive intra- and interspecific, both intra- and interploidy breeding relationships were established, without previous assumptions on the compatibility behavior of the studied germplasm. Pollen–pistil relationships were analyzed at the individual genotype/accession/family level. In two seasons, 828 intra- and interspecific genotypic combinations were performed, using accessions of the wild potatoes Solanum chacoense Bitter (2n = 2x = 24), S. gourlayi Hawkes (2n = 2x = 24; 2n = 4x = 48), and S. spegazzinii Bitter (2n = 2x = 24), full-sibling (hereinafter “full-sib”) families (2n = 2x = 24) within/between the latter two diploids, and S. tuberosum L. (2n = 4x = 48) cultivars. Pollen–pistil incompatibility occurred in the upper first third of the style (I1/3) in all selfed diploids. In both the intra- and interspecific combinations, the most frequent relationship was compatibility, followed by I1/3, but incompatibility also occurred in the stigma and the style (middle third and bottom third). We observed segregation for these relationships in full-sib families, and unilateral and bilateral incompatibility in reciprocal crosses between functional SI genotypes. Cross-incompatibility in potatoes is, apparently, controlled by genes independent of the S-locus or its S-haplotype recognition region (although molecular evidence is needed to confirm it), with segregation even within accessions.