Draft genome sequence of cauliflower(Brassica oleracea L.var.botrytis)provides new insights into the C genome in Brassica species

Cauliflower is an important variety of Brassica oleracea and is planted worldwide.Here,the high-quality genome sequence of cauliflower was reported.The assembled cauliflower genome was 584.60 Mb in size,with a contig N50 of 2.11 Mb,and contained 47,772 genes;56.65%of the genome was composed of repetitive sequences.Among these sequences,long terminal repeats(LTRs)were the most abundant(32.71%of the genome),followed by transposable elements(TEs)(12.62%).Comparative genomic analysis confirmed that after an ancient paleohexaploidy(γ)event,cauliflower underwent two whole-genome duplication(WGD)events shared with Arabidopsis and an additional whole-genome triplication(WGT)event shared with other Brassica species.The present cultivated cauliflower diverged from the ancestral B.oleracea species~3.0 million years ago(Mya).The speciation of cauliflower(~2.0 Mya)was later than that of B.oleracea L.var.capitata(approximately 2.6 Mya)and other Brassica species(over 2.0 Mya).Chromosome no.03 of cauliflower shared the most syntenic blocks with the A,B,and C genomes of Brassica species and its eight other chromosomes,implying that chromosome no.03 might be the most ancient one in the cauliflower genome,which was consistent with the chromosome being inherited from the common ancestor of Brassica species.In addition,2,718 specific genes,228 expanded genes,2 contracted genes,and 1,065 positively selected genes in cauliflower were identified and functionally annotated.These findings provide new insights into the genomic diversity of Brassica species and serve as a valuable reference for molecular breeding of cauliflower.

Disruption of the bHLH transcription factor Abnormal Tapetum 1 causes male sterility in watermelon

Although male sterility has been identified as a useful trait for hybrid vigor utilization and hybrid seed production,its underlying molecular mechanisms in Cucurbitaceae species are still largely unclear.Here,a spontaneous male-sterile watermelon mutant,Se18,was reported to have abnormal tapetum development,which resulted in completely aborted pollen grains.Map-based cloning demonstrated that the causal gene Citrullus lanatus Abnormal Tapetum 1(ClATM1)encodes a basic helix-loop-helix(bHLH)transcription factor with a 10-bp deletion and produces a truncated protein without the bHLH interaction and functional(BIF)domain in Se18 plants.qRT–PCR and RNA in situ hybridization showed that ClATM1 is specifically expressed in the tapetum layer and in microsporocytes during stages 6–8a of anther development.The genetic function of ClATM1 in regulating anther development was verified by CRISPR/Cas9-mediated mutagenesis.Moreover,ClATM1 was significantly downregulated in the Se18 mutant,displaying a clear dose effect at the transcriptional level.Subsequent dual-luciferase reporter,β-glucuronidase(GUS)activity,and yeast one-hybrid assays indicated that ClATM1 could activate its own transcriptional expression through promoter binding.Collectively,ClATM1 is the first male sterility gene cloned from watermelon,and its self-regulatory activity provides new insights into the molecular mechanism underlying anther development in plants.