Flowering time plays a vital role in determining the life-cycle period, yield, and seed quality of rapeseed (Brassica napus L.) in certain environments. Quantitative trait locus (QTL) mapping to identify the genetic architecture of genes controlling flowering time helps accelerate the early maturity breeding process. In this study, simple sequence repeats (SSR) and specific-locus amplified fragment sequencing (SLAF-seq) technologies were adopted to map the QTLs for flowering time in four environments. As a result, three target intervals, FTA09, FTA10, and FTC05 were identified. Among this, FTA09 was considered as a novel interval, FTA10 and FTC05 as stable regions. Based on the parental re-sequencing data, 7,022 single nucleotide polymorphisms (SNPs) and 2,195 insertion-deletions (InDels) between the two parents were identified in these three target regions. A total of 186 genes possessed genetic variations in these intervals, 14 of which were related to flowering time involved in photoperiod, circadian clock, vernalization, and gibberellin pathways. Six InDel markers linked to flowering time were developed in the three target intervals, indicating that the results were credible in this study. These results laid a good foundation for further genetic studies on flowering-time regulation in B. napus L.

Pectin is a major polysaccharide component that promotes plant growth and fiber elongation in cotton. In previous studies, the galacturonosyltransferase-like (GATL) gene family has been shown to be involved in pectin synthesis. However, few studies have been performed on cotton GATL genes. Here, a total of 33, 17, and 16 GATL genes were respectively identified in Gossypium hirsutum, Gossypium raimondii, and Gossypium arboreum. In multiple plant species, phylogenetic analysis divided GATL genes into five groups named GATL-a to GATL-e, and the number of groups was found to gradually change over evolution. Whole genome duplication (WGD) and segmental duplication played a significant role in the expansion of the GATL gene family in G. hirsutum. Selection pressure analyses revealed that GATL-a and GATL-b groups underwent a great positive selection pressure during evolution. Moreover, the expression patterns revealed that most of highly expressed GhGATL genes belong to GATL-a and GATL-b groups, which have more segmental duplications and larger positive selection value, suggesting that these genes may play an important role in the evolution of cotton plants. We overexpressed GhGATL2, GhGATL9, GhGATL12, and GhGATL15 in Arabidopsis and silenced the GhGATL15 gene in cotton through a virus induced gene silencing assay (VIGS). The transgenic and VIGS lines showed significant differences in stem diameter, epidermal hair length, stamen length, seed size, and fiber length than the control plant. In addition, the pectin content test proved that the pectin was significantly increased in the transgenic lines and reduced in VIGS plants, demonstrating that GhGATL genes have similar functions and act on the pectin synthesis to regulate plant growth and fiber elongation. In summary, we performed a comprehensive analysis of GhGATL genes in G. hirsutum including evolution, structure and function, in order to better understand GhGATL genes in cotton for further studies.

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Plasmodiophora brassicae infection leads to hypertrophy of host roots and subsequent formation of galls, causing huge economic losses to agricultural producers of Cruciferae plants. Ethylene (ET) has been reported to play a vital role against necrotrophic pathogens in the classic immunity system. More clues suggested that the defense to pathogens in roots may be different from the acrial. The ET pathway may play a positive role in the infection of P. brassicae, as shown by recent transcriptome profiling. However, the molecular basis of ET remains poorly understood. In this study, we investigated the potential role of ethylene against P. brassicae infection in an ein3/eil1 double-mutant of Arabidopsis thaliana (A. thaliana). After infection, ein3/eil1 (Disease Index/DI: 93) showed more susceptibility compared with wild type (DI: 75). Then, we inoculated A. thaliana Columbia-0 (Col-0) with P. brassicae by 1-aminocyclopropane-1-carboxylic acid (ACC) and pyrazinamide (PZA), respectively. It was found that the symptoms of infected roots with ACC were more serious than those with PZA at 20 dpi (day post infection). However, the DI were almost the same in different treatments at 30 dpi. WRKY75 can be directly regulated by ET and was upregulated at 7 dpi with ACC, as shown by qRT-PCR. The wrky75-c mutant of A. thaliana (DI: 93.75) was more susceptible than the wild type in Arabidopsis. Thus, our work reveals the dual roles of ET in infection of P. brassicae and provides evidence of ET in root defense against pathogens.

Harvest index (HI) is a complex and vital agronomic trait that is closely related to the economic benefits of rapeseed. In this study, we measured the HI and 13 HI-related agronomic traits of 104 core breeding lines of rapeseed during 3 years and sequenced the populations using the Bnapus50K array. The phenotypic analyses showed the complex connections among HI and other traits. A total of 212 significant SNPs related to the traits and 22 stable SNPs were identified. Four SNPs, A01_1783685 (PH and SYP), C06_26638717 (PH and NSS), C03_4731660 (MIL and MINS), and C09_36899682 (PH and BYP), were identified as potential pleiotropic loci. Compared to previous reports, 49 consensus loci were obtained that were related to PH, TSW, NSP, BAI, NSS, SL, BN, MINS, SYP, and BYP. Twelve stable SNPs were detected as promising novel loci related to BN (A05_19368584 and A05_19764389), SL (A06_23598999, A06_23608274, and C07_38735522), PH (C04_47349279, C04_47585236, and C09_36899680), MINS (C05_6251826), NSS (C06_22559430 and C06_22570315), and HI (C05_6554451). In addition, 39 putative genes were identified in the candidate intervals. This study provides novel insights into the genetic mechanisms of HI and HI-related traits, and lays a foundation for molecular marker development and casual gene cloning to improve the harvest index of rapeseed.