Dosage Effects Of Gene Expression In Brassica Napus And Development Of Brassica Oleracea-nigra Addition Lines

Polyploidy occurs in more than 70% flowering plants,and is an important evolutionary process for plant speciation.The initial stage of polyploidization is accompanied by various genetic and/or epigenetic changes along with the gene dosage balance and gene regulatory network resulting in changes on gene expression levels.Such profound changes may enhance the fitness and adaptability for polyploids.However,we still know very little about dosage-balance regulation contributing to gene expression and evolution,and the underlying causes of dosage dependent/independent genes were largely elusive.In this study,some of the cultivated Brassica species were used to investigate the effects of gene/genome dosage on gene expression and interaction.On the one hand,for euploidy,the gene expressions of a serial Brassica hybrids/polyploids(AC,AAC,CCA,CCAA)with different copies of A and C subgenomes and their parental diploids were analyzed detected by RNA-seq to reveal genome-wide genome dosage balance regulates gene expressions.On the other hand,we aimed to development of a complete set of Brassica oleracea-nigra MAALs,for which could be used to study not only dosage-balance regulation of aneuploidy(monosome),but also a useful tool for genetic study and breeding.The main results are as follows: 1.Effects of dosage-balance on gene expression and evolution.To investigate the effects of genome dosage variation on gene expression and interaction,a serial Brassica hybrids/polyploids(AC,AAC,CCA,CCAA)with different copies of A and C subgenomes from the same two parents of B.rapa and B.oleracea were synthesized and analyzed by RNA-Seq.The expression changes of A-and C-subgenome genes were consistent with dosage alterations.Dosage-dependent and-independent genes were grouped according to the correlations between dosage variations and gene expressions.Expression levels of dosage-dependent genes were strongly correlated with dosage changes and mainly contributed to dosage effects,while those of dosage-independent genes gave weak correlations with dosage variations and mostly facilitated dosage compensation.More protein-protein interactions were detected for dosage-independent genes than dosage-dependent ones,as predicted by the dosage balance hypothesis.Dosage-dependent genes more likely impacted the expressions by trans effects,whereas dosage-independent genes preferred to play by cis effects.Furthermore,dosage-dependent genes were mainly associated with the basic biological processes that maybe to maintain the stability of the growth and development,while dosage-independent genes were more enriched in the stress response related processes and probably to accelerate adaptation.The present comprehensive analysis of gene expression dependent/independent on dosage alterations in Brassica polyploids provided new insights into gene/genome dosage-balance regulation of gene expressions.2.Development of Brassica oleracea-nigra monosomic alien addition lines.To development of B.oleracea-nigra MAALs,the triploid F1 hybrid(2n = 26,CCB)obtained previously from the cross B.oleracea(2n = 18,CC)× B.nigra was used as the maternal parent and backcrossed successively to parental B.oleracea.The progenies in BC1 to BC3 generations were analyzed by the methods of FISH and SSR markers to screen the MAALs with each of eight different B-genome chromosomes added to C genome(2n = 19,CC+1B1-8),and seven different MAALs were established,except for the one with chromosome B2 which existed in one triple addition.Most of these MAALs were distinguishable morphologically from each other,as they expressed the characters from B.nigra differently and at variable extents.The alien chromosome remained unpaired as a univalent in 86.24% pollen mother cells at diakinesis or metaphase I,and formed a trivalent with two C-genome chromosomes in 13.76% cells.Transmission frequency of all the added chromosomes was far higher through the ovules(averagely 14.40%)than the pollen(averagely 2.64%).The B1,B4 and B5 chromosomes were transmitted by female at much higher rates(22.38-30.00%)than the other four(B3,B6,B7,B8)(5.04-8.42%).The MAALs should be valuable for exploiting the genome structure and evolution and using the useful traits of B.nigra.