Genetic Analysis Of Flower Buds Cluster In Brassica Napus

Rapeseed is world's main oil,feed and energy crops.With the change of labor structure,the improvement of productivity level and the adjustment of agricultural structure,there are also many problems in rapeseed production,such as insufficient labor force and low degree of mechanization,which seriously restricts the development of China's rapeseed industry.The flower buds cluster mutants of studied in this paper have the advantages of no branching or short branching after flowering,flower bud clustering,and the concentrated maturity period.They are not only suitable for planting with high density,but also suitable for increasing the yield potential of rapeseed,and most significant advantage is that they can greatly improve the mechanized harvesting degree of rapeseed.In this paper,the clustering mutants of Brassica napus L.are used as experimental materials,and the genetic mechanism is analyzed by morphological analysis,Bulk Segregant Analysis?BSA?sequencing and transcriptome sequencing.The main results are as follows:?1?Morphological observation and agronomic trait analysis at different growth stages.At the seedling stage,the wild-type and flower bud cluster mutants began to show phenotypic differences at about 15 days,the leaf primordia of the mutants started faster than the wild type,and the difference continued to expand.In the seedling period,the number of leaves of the mutants was significantly higher than that of wild type;in the bolting stage,the shoot apical meristem?SAM?of the mutant is more swollen than the wild type;at the flowering stage,the inflorescence of the mutant showed multiple apical meristems,and the adhesion are shown between main stem and branches.At the maturity stage,the pods number of mutant increased and the pod density significantly increased.In summary,the cause of flower bud clustering might be that the SAM of the flower bud cluster mutants continues to undergo abnormal division and differentiation,which leads to the simultaneous growth of multiple apical meristems.?2?BSA.In the F_2:3 population of the flower bud cluster mutant and the wild type lines,two phenotypic extreme strains were screened to construct a progeny mixed pool for BSA sequencing analysis..A total of 62,729,271 SNPs and 3,085,197 InDels were detected.Six significant association regions were detected by association analysis,in which a total of 799candidate genes were mined.Through the functional annotation and Mapman network analysis of candidate genes,most of which were involved in transcriptional regulation,protein modification,protein degradation and other pathways.Most of the transcriptional factors were clustered in MYB,MADS,AP2,C2H2 and bHLH,and these families are directly or indirectly involved in the regulation of SAM.The E3 ligase SCF complex in the ubiquitin-proteasome system localized to the peak of a significant associated site,which indicated that the SCF complex might play a key role in SAM network regulation.?3?Combining BSA and comparative transcriptome analysis.Through the interaction network,candidate genes in BSA significant association regions and differentially expressed transcription factors in transcriptome sequencing can directly or indirectly interact to regulate the reported SAM genes.IAA8 is a candidate gene shared by BSA and transcriptome,and auxin plays a key role in regulating RPS10B to promote axillary bud development;PGY cooperates with REV,KAN1 and KAN2 to regulate leaf primordial cell differentiation;KAN interacts with AS1 and AS2 to regulate the formation of lateral organ boundaries;as a component of CSN,FUS12 participates in photomorphogenesis and auxin responses by regulating the activity of E3 ligase;SE and AGO4 regulate meristem activity and paraxial leaf differentiation by regulating PHB and KNOX expression;SPL3 interacts with the CLV-WUS pathway and the NAC family and the KNOX family through CRN.The results of integrated BSA and transcriptome analysis indicated that these key genes and transcription factors may inhibit the growth regulation between the apical meristem and the leaf primordium boundary region,which cause the SAM losing its apical dominance and then laterally become larger.The leaf primordia initiation site changes,resulting in the appearance of multiple SAM and flower bud clustered phenotypes.The results obtained some key genes and transcription factors regulating the formation of flower buds,which was supplemented and improved by the regulatory mechanism of transcriptome analysis.In this study,morphological observation and BSA analysis combined with transcriptome sequencing revealed the mechanism of flower bud clustering,further confirming that flower buds cluster is due to SAM regulation network abnormality,leaf primordia initiation site changes,SAM loses apical dominance,and thus multiple minute organization.The study of cluster bud mutants laid the foundation for the selection of rapeseed suitable for mechanized harvesting.