Abstract
Distant hybridization usually leads to female sterility of the hybrid but the mechanism behind this is poorly understood. Complete pistil abortion but normal male fertility was shown by one Brassica napus-Orychophragmus violaceus monosomic alien addition line (MA, AACC + 1 IO, 2n = 39) produced previously. To study the effect of a single O. violaceus chromosome addition on pistil development in different genetic backgrounds, hybrids between the MA and B. carinata (BBCC), B. juncea (AABB), and two synthetic hexaploids (AABBCC) were firstly produced in this study which show complete female sterility. A microspore culture was further performed to produce the haploid monosomic alien addition line (HMA, AC + 1 IO, 2n = 20) and disomic addition line (DA, AACC + 2 IO, 2n = 40) together with haploid (H, AC, 2n = 19) and double haploid (DH, AACC, 2n = 38) plants of B. napus from MA to investigate the dosage effect of the alien O. violaceus chromosome on pistil development and gene expression. Compared to MA, the development of the pistils of DA and HMA was completely or partially recovered, in which the pistils could swell and elongate to a normal shape after open pollination, although no seeds were produced. Comparative RNA-seq analyses revealed that the numbers of the differentially expressed genes (DEGs) were significantly different, dosage-dependent, and consistent with the phenotypic difference in pairwise comparisons of HMA vs. H, DA vs. DH, MA vs. DH, MA vs. DA, and MA vs. HMA. The gene ontology (GO) enrichment analysis of DEGs showed that a number of genes involved in the development of the gynoecium, embryo sac, ovule, and integuments. Particularly, several common DEGs for pistil development shared in HMA vs. H and DA vs. DH showed functions in genotoxic stress response, auxin transport, and signaling and adaxial/abaxial axis specification. The results provided updated information for the molecular mechanisms behind the gynoecium development of B. napus responding to the dosage of alien O. violaceus chromosomes.
Highlights
The development of a pistil begins with one or more fused carpels which have evolved from leaves [1]
In order to explore the effect of the alien O. violaceus chromosome on gynoecia development in different genomic backgrounds, besides B. napus, hybrids between the female sterile monosomic alien addition line (MA) and B. carinata (BBCC), B. juncea (AABB), and synthetic hexaploid 1 (AABBCC) derived from B. carinata and B. rapa (AA) [32], and hexaploid 2 from the sequential hybridization of three Brassica diploids [33], were produced
We further investigated the common differentially expressed genes (DEGs) between disomic additions (DA) vs. double haploid (DH) and haploid monosomic addition (HMA) vs. H which are involved in embryo development and post-embryonic development
Summary
The development of a pistil begins with one or more fused carpels which have evolved from leaves [1]. In the tip of the nucellus, the megaspore mother cell is differentiated from a hypodermal cell and undergoes meiosis followed by three rounds of mitosis to form a mature embryo sac comprised of three antipodal cells, two medial polar nuclei, one egg cell, and two synergid cells [6]. Pistil development is a complex process that requires several tissues to acquire specific identities in specific places. This process may be realized through the regulatory network formed by genes and hormones, including Auxins, cytokinins (CKs), gibberellins (GAs), and brassinosteroids (BRs) [7,8]. The genes can affect hormonal pathways at different levels, including biosynthesis, transport, and signaling, and in turn, the hormones can influence the transcriptional regulation of the genes
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