Key genes and mechanisms underlying natural variation of silique length in oilseed rape(Brassica napus L.)germplasm

Silique length influences seed yield in oilseed rape.It shows extensive variation in germplasm resources,and identifying the underlying genes and regulatory mechanisms would advance breeding for the trait.In the present study,a genome-wide association study(GWAS)using 331 core accessions planted in 10 environments revealed 13 loci associated with silique length on chromosomes A01,A04,A07,A09,and C03,explaining 6.2%–19.2%of phenotypic variance.Physiological analysis showed that silique length variation was attributable to differences in silique growth rate and/or duration before four weeks after flowering,with levels of endogenous phytohormones(auxin,ethylene,and GA24,GA12,and GA44)playing an important role.Cytological analysis showed that silique length variation was due mainly to differences in cell number followed by cell size.Transcriptomic analysis of two pools of silique walls with opposite length extremes revealed 3248 differentially expressed genes(DEGs).These DEGs were enriched in several pathways(such as cell wall,cell division,and hormone metabolism)associated with cell proliferation and expansion and silique development.Integrating GWAS,RNA-seq,and functional annotation results revealed 15 candidate genes for the major associated locus q SL.A09-3.Of these,Bna A9.ARF18 and Bna A9.CYP78 A9 were validated by haplotype analysis followed by candidate gene association.Sequence variation in the coding region of Bna A9.ARF18 and expression of Bna A9.CYP78 A9 in silique walls were strongly associated with silique length.Our results provide an explanation for the natural variation of silique length in oilseed rape germplasm and offer useful information for its improvement.

Synergistic influence of the capture effect of western flower thrips(Frankliniella occidentalis)induced by proportional yellow-green light in the greenhouse

To clarify the influence of yellow,green,and proportional yellow-green light on the capture effect,western flower thrips,Frankliniella occidentalis(Pergande),were captured using different self-made light sources in a greenhouse.The bio-activity capture effect of thrips was regulated by light and analyzed to determine the reasons for the changes in their capture by light.The results showed that the thrips’capture effect induced by different light sources with the same brightness was positively correlated with night temperature.When the average night temperature was 27℃(19:00-21:30),the capture effect was optimal,indicating that the coupling effect of light temperature can regulate the capture effect of thrips.Green light intensified and yellow light inhibited the visual trend sensitivity of thrips to yellow-green light of differing proportions.The capture effect trapped by a green-yellow light ratio of 4:1 was optimal(1088.00 individuals in night time),while that of yellow light was the worst(456.67 individuals/night),thus,indicating that visual trend sensitivity of thrips to green light was higher than that of yellow light.Such differences originated from the differences in the photoelectric thermal conversion effect of spectral optical properties,and the spectral photo-thermal effect was the main reason that thrips produced a light-trapped behavior.Night light enhanced the sensitivity of thrips’responses to a white adhesive board during the daytime,and the effect of yellow light intensity was the strongest(1563.00 individuals in the daytime),while that of green light was the weakest(75.33 individuals in the day time).Additionally,yellow light intensified while green light inhibited the regulatory effect of different proportions of yellow-green light on the bio-activity of thrips.However,the capture effect of day and night corresponding to 4:1 green-yellow light was the best(2019.67 individuals in day and night).The function of the photo-thermal effect on the capture effect of thrips was affected by the decrease in night temperature,but the photo-electro-thermal effects of night light intensified the bio-activity of thrips in the daytime and enhanced their color sensitivity.The results provide a theoretical basis for the development of pest light induction equipment.

A Novel Chimeric Mitochondrial Gene Confers Cytoplasmic Effects on Seed Oil Content in Polyploid Rapeseed (Brassica napus)

Cytoplasmic effects (CEs) have been discovered to influence a diverse array of agronomic traits in crops, and understanding the underlying mechanisms can help accelerate breeding programs. Seed oil content (SOC) is of great agricultural, nutritional, and economic importance. However, the genetic basis of CEs on SOC (CE-SOC) remains enigmatic. In this study, we use an optimized approach to sequence the cytoplasmic (plastid and mitochondrial) genomes of allotetraploid oilseed rape (Brassica napus) cultivars, 51218 and 56366, that bear contrasting CE-SOC. By combining comparative genomics and genome-wide transcriptome analysis, we identify mitochondria-encoded orf188 as a potential CE-SOC determinant gene. Functional analyses in the model system Arabidopsis thaliana and rapeseed demonstrated that orf188 governs CE-SOC and could significantly increase SOC, strikingly, through promoting the yield of ATP. Consistent with this finding, transcriptional profiling with microarray and RNA sequencing revealed that orf188 affects transcriptional reprogramming of mitochondrial energy metabolism to facilitate ATP production. Intriguingly, orf188 is a previously uncharacterized chimeric gene, and the presence of this genetic novelty endows rapeseed with positive CE-SOC. Our results shed light on the molecular basis of CEs on a key quantitative trait in polyploid crops and enrich the theory of maternal control of oil content, providing new scientific guidance for breeding high-oil rapeseed germplasms.

Genetic dissection of root morphological traits as related to potassium use efficiency in rapeseed under two contrasting potassium levels by hydroponics

To reveal the genetic basis of potassium use efficiency(KUE) in rapeseed, root morphology(RM), biomass and KUE-related traits were measured in a recombinant inbred line population with 175 F7 lines that were subjected to high-potassium(HK) and low-potassium(LK) treatments by hydroponics. A total of 109 significant QTLs were identified to be associated with the examined traits. Sixty-one of these QTLs were integrated into nine stable QTLs. The higher heritability for RM and biomass traits and lower heritability for KUE-related traits, as well as nine stable QTLs for RM traits and only two for KUE-related traits,suggested that regulating RM traits would be more effective than selecting KUE traits directly to improve KUE by markerassisted selection. Furthermore, the integration of stable QTLs identified in the HK, LK, high-nitrogen(HN) and low-nitrogen(LN) conditions gave 10 QTL clusters. Seven of these clusters were classified into major QTLs that explained 7.4%–23.7% of the total phenotypic variation. Five of the major QTL clusters were detected under all of the treated conditions, and four clusters were specifically detected under the LK and LN conditions. These common and specific QTL clusters may be useful for the simultaneous improvement of multiple traits by marker-assisted selection.