Rapeseed (Brassica napus L.) is a model plant for polyploid crop research and the second-leading source of vegetable oil worldwide. Silique length (SL) and seed weight are two important yield-influencing traits in rapeseed. Using map-based cloning, we isolated qSLWA9, which encodes a P450 monooxygenase (BnaA9.-CYP78A9) and functions as a positive regulator of SL. The expression level of BnaA9.CYP78A9 in silique valves of the long-silique variety is much higher than that in the regular-silique variety, which results in elongated cells and a prolonged phase of silique elongation. Plants of the long-silique variety and transgenic plants with high expression of BnaA9.CYP78A9 had a higher concentration of auxin in the developing silique; this induced a number of auxin-related genes but no genes in well-known auxin biosynthesis pathways, suggesting that BnaA9.CYP78A9 may influence auxin concentration by affecting auxin metabolism or an unknown auxin biosynthesis pathway. A 3.7-kb CACTA-like transposable element (TE) inserted in the 3.9-kb upstream regulatory sequence of BnaA9.CYP78A9 elevates the expression level, suggesting that the CACTA-like TE acts as an enhancer to stimulate high gene expression and silique elongation. Marker and sequence analysis revealed that the TE in B. napus had recently been introgressed from Brassica rapa by interspecific hybridization. The insertion of the TE is consistently associated with long siliques and large seeds in both B. napus and B. rapa collections. However, the frequency of the CACTA-like TE in rapeseed varieties is still very low, suggesting that this allele has not been widely used in rapeseed breeding programs and would be invaluable for yield improvement in rapeseed breeding.
Summary Plant architecture is the key factor affecting overall yield in many crops. The genetic basis underlying plant architecture in rapeseed (Brassica napus), a key global oil crop, is elusive. We characterized an ethyl methanesulfonate (EMS)‐mutagenized rapeseed mutant, sca, which had multiple phenotypic alterations, including crinkled leaves, semi‐dwarf stature, narrow branch angles and upward‐standing siliques. We identified the underlying gene, which encodes an Aux/IAA protein (BnaA3.IAA7). A G‐to‐A mutation changed the glycine at the 84th position to glutamic acid (G84E), disrupting the conserved degron motif GWPPV and reducing the affinity between BnaA3.IAA7 and TIR1 (TRANSPORT INHIBITOR RESPONSE 1) in an auxin dosage‐dependent manner. This change repressed the degradation of BnaA3.IAA7 and therefore repressed auxin signaling at low levels of auxin that reduced the length of internodes. The G84E mutation reduced branch angles by enhancing the gravitropic response. The heterozygote +/sca closely resembled a proposed ideal plant architecture, displaying strong yield heterosis through single‐locus overdominance by improving multiple component traits. Our findings demonstrate that a weak gain‐of‐function mutation in BnaA3.IAA7 contributes to yield heterosis by improving plant architecture and would be valuable for breeding superior rapeseed hybrid cultivars and such a mutation may increase the yield in other Brassica crops.
Timely flowering is important for seed formation and maximization of rapeseed (Brassica napus) yield. Here, we performed flowering-time quantitative trait loci (QTL) mapping using a double haploid (DH) population grown in three environments to study the genetic architecture. Brassica 60 K Illumina Infinium™ single nucleotide polymorphism (SNP) array and simple sequence repeat (SSR) markers were used for genotyping of the DH population, and a high-density genetic linkage map was constructed. QTL analysis of flowering time from the three environments revealed five consensus QTLs, including two major QTLs. A major QTL located on chromosome A03 was detected specifically in the semi-winter rapeseed growing region, and the one on chromosome C08 was detected in all environments. Ribonucleic acid sequencing (RNA-seq) was performed on the parents’ leaves at seven time-points in a day to determine differentially expressed genes (DEGs). The biological processes and pathways with significant enrichment of DEGs were obtained. The DEGs in the QTL intervals were analyzed, and four flowering time-related candidate genes were found. These results lay a foundation for the genetic regulation of rapeseed flowering time and create a rapeseed gene expression library for seven time-points in a day.
Roses, which are one of the world’s most important ornamental plants, are often damaged by pathogens, resulting in serious economic losses. As a subclass of the disease resistance gene family of plant nucleotide-binding oligomerization domain (NOD)-like receptors, TIR-NBS-LRR (TNL) genes play a vital role in identifying pathogen effectors and activating defense responses. However, a systematic analysis of the TNL gene family is rarely reported in roses. Herein, 96 intact TNL genes were identified in Rosa chinensis. Their phylogenies, physicochemical characteristics, gene structures, conserved domains and motifs, promoter cis-elements, microRNA binding sites, and intra- and interspecific collinearity relationships were analyzed. An expression analysis using transcriptome data revealed that RcTNL genes were dominantly expressed in leaves. Some RcTNL genes responded to gibberellin, jasmonic acid, salicylic acid, Botrytis cinerea, Podosphaera pannosa, and Marssonina rosae (M. rosae); the RcTNL23 gene responded significantly to three hormones and three pathogens, and exhibited an upregulated expression. Furthermore, the black spot pathogen was identified as M. rosae. After inoculating rose leaves, an expression pattern analysis of the RcTNL genes suggested that they act during different periods of pathogen infection. The present study lays the foundations for an in-depth investigation of the TNL gene function and the mining of disease resistance genes in roses.
Photosystem II (PSII) is an important component of the chloroplast. The PSII repair cycle is crucial for the relief of photoinhibition and may be advantageous when improving stress resistance and photosynthetic efficiency. Lethal genes are widely used in the efficiency detection and method improvement of gene editing. In the present study, we identified the naturally occurring lethal mutant 7-521Y with etiolated cotyledons in Brassica napus, controlled by double-recessive genes (named cyd1 and cyd2). By combining whole-genome resequencing and map-based cloning, CYD1 was fine-mapped to a 29 kb genomic region using 15,167 etiolated individuals. Through cosegregation analysis and functional verification of the transgene, BnaC06.FtsH1 was determined to be the target gene; it encodes an filamentation temperature sensitive protein H 1 (FtsH1) hydrolase that degrades damaged PSII D1 in Arabidopsis thaliana. The expression of BnaC06.FtsH1 was high in the cotyledons, leaves, and flowers of B. napus, and localized in the chloroplasts. In addition, the expression of EngA (upstream regulation gene of FtsH) increased and D1 decreased in 7-521Y. Double mutants of FtsH1 and FtsH5 were lethal in A. thaliana. Through phylogenetic analysis, the loss of FtsH5 was identified in Brassica, and the remaining FtsH1 was required for PSII repair cycle. CYD2 may be a homologous gene of FtsH1 on chromosome A07 of B. napus. Our study provides new insights into lethal mutants, the findings may help improve the efficiency of the PSII repair cycle and biomass accumulation in oilseed rape.
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