Helitron-like transposons contributed to the mating system transition from out-crossing to self-fertilizing in polyploid Brassica napus L.

Abstract

The mating system transition in polyploid Brassica napus (AACC) from out-crossing to selfing is a typical trait to differentiate it from their diploid progenitors. Elucidating the mechanism of mating system transition has profound consequences for understanding the speciation and evolution in B. napus. Functional complementation experiment has shown that the insertion of 3.6 kb into the promoter of self-incompatibility male determining gene, BnSP11-1 leads to its loss of function in B. napus. The inserted fragment was found to be a non-autonomous Helitron transposon. Further analysis showed that the inserted 3.6 kb non-autonomous Helitron transposon was widely distributed in B. napus accessions which contain the S haplotype BnS-1. Through promoter deletion analysis, an enhancer and a putative cis-regulatory element (TTCTA) that were required for spatio-temporal specific expression of BnSP11-1 were identified, and both might be disrupted by the insertion of Helitron transposon. We suggested that the insertion of Helitron transposons in the promoter of BnSP11-1 gene had altered the mating system and might facilitated the speciation of B. napus. Our findings have profound consequences for understanding the self-compatibility in B. napus as well as for the trait variations during evolutionary process of plant polyploidization.

Generation of Transgenic Self-Incompatible Arabidopsis thaliana Shows a Genus-Specific Preference for Self-Incompatibility Genes

“…As the BnARC1 transgene was previously shown to be functional in the A. thaliana Col-0 background [43], it is more likely that BnSCR1 or BnSRK1 are not functional in A. thaliana. Similar, the BnSCR1 construct was found to be functional in B. napus [46], and so BnSRK1 would be the only previously untested construct. One other possible reason is that Arabidopsis and Brassica species may not completely share the same SRK-mediated self-incompatibility signaling pathway.…”

“…These differences may potentially be due to B. napus SRK 1 activity, as B. napus ARC1 was previously shown to interact with A. lyrata SRK, and the A. lyrata SCRb-SRKb and B. napus ARC1 transgenes produced self-incompatible Col-0 transgenic plants [43,53]. Ideally, the potential activity of the B. napus transgenes could be tested by reciprocal pollinations between the A. thaliana Col-0 BnSCR1-BnSRK1-BnARC1 lines and the B. napus S1 haplotype transgenic line [46]. However, large physical differences in pollen and pistil sizes between these species (Supplementary Figure S2, [38]) as well as potential complications from interspecies crosses may obscure any self-incompatibility reactions.…”

“…The functional promoter and CDS of BrSP11-47 (the CDS sequence is the same as BnSCR 1 ) was amplified from the pCAMBIA2301-1+4 vector [46]. And the Nopaline synthase polyadenylation signal (NosT) was amplified from the pCAMBIA2301 vector used as the terminator of BnSCR 1 [64].…”

“…Nevertheless, stable self-incompatible A. thaliana were finally generated in the Col-0 ecotype when AlARC1 or BnARC1 were expressed along with the AlSCRb-AlSRKb transgenes [43].Here, we further examine the question of whether Brassica and Arabidopsis self-incompatibility genes can share a common self-incompatibility signaling pathway in transgenic A. thaliana using a new set of self-incompatibility genes from B. napus and A. halleri. The B. napus S 1 -haplotype SCR/SP11 and SRK genes [44][45][46] along with BnARC1 were transformed into two A. thaliana accessions, Col-0 and C24. As both the pollen (BnSCR/SP11 1 ) and stigma (BnSRK 1 , BnARC1) factors were included for this study, this differs from a previous study [38] where only stigma B. napus factors were transformed.…”

An Epigenetic LTR-retrotransposon insertion in the upstream region ofBnSHP1.A9controls quantitative pod shattering resistance inBrassica napus

“…TEs are frequent found in B. napus genomes (Chalhoub et al, 2014; Sun et al, 2017) and have been implicated in DNA methylation and H3K9me2 modification (Eichten et al, 2012; Gent et al, 2013), altering gene expression both genetically and epigenetically (Cui and Cao, 2014). In fact, several oilseed rape genes related to morphological or physiological traits have evolved from TE insertions (Hou et al, 2012; Zhang et al, 2015; Gao et al, 2016; Shi et al, 2019). The current study implies that DNA methylation of the Copia-LTR insertion spreads to BnSHP1.A9 cis-regulatory region.…”