Complex Molecular Evolution and Expression of Expansin Gene Families in Three Basic Diploid Species of Brassica

Abstract

Expansins are a kind of structural proteins of the plant cell wall, and they enlarge cells by loosening the cell walls. Therefore, expansins are involved in many growth and development processes. The complete genomic sequences of Brassica rapa, Brassica oleracea and Brassica nigra provide effective platforms for researchers to study expansin genes, and can be compared with analogues in Arabidopsis thaliana. This study identified and characterized expansin families in B. rapa, B. oleracea, and B. nigra. Through the comparative analysis of phylogeny, gene structure, and physicochemical properties, the expansin families were divided into four subfamilies, and then their expansion patterns and evolution details were explored accordingly. Results showed that after the three species underwent independent evolution following their separation from A. thaliana, the expansin families in the three species had increased similarities but fewer divergences. By searching divergences of promoters and coding sequences, significant positive correlations were revealed among orthologs in A. thaliana and the three basic species. Subsequently, differential expressions indicated extensive functional divergences in the expansin families of the three species, especially in reproductive development. Hence, these results support the molecular evolution of basic Brassica species, potential functions of these genes, and genetic improvement of related crops.

Two Expansin Genes, AtEXPA4 and AtEXPB5, Are Redundantly Required for Pollen Tube Growth and AtEXPA4 Is Involved in Primary Root Elongation in Arabidopsis thaliana

“…Through the analysis of domains on the Pfam website ( (accessed on 21 March 2018)), we confirmed that both AtEXPA4 and AtEXPB5 contain DPBB_1 and Pollen_allerg_1, which have typical domains of the expansin gene family ( Figure S1 ) [ 12 ].qRT-PCR and GUS reporting system were used to explore spatial and temporal expression of them. The results showed that AtEXPA4 seemed to expressed ubiquitously ( Figure 1 A), but its expression level was higher in inflorescences and roots ( Figure 1 A,B).…”

“…Expansins can weaken non-covalent bonds between cell wall polysaccharides, thereby promoting slippage and relaxation of cellulose microfibers, resulting in cell wall extension and cell expansion [ 10 , 11 ]. Expansins usually have two typical domains, DPBB_1 and Pollen_allerg_1, and most of expansins have signal peptides [ 12 ]. DPBB_1 domain is often related to family-45 glycosyl hydrolase (GH45), and contains a conserved region that has the double-psi beta-barrel (DPBB) fold [ 13 , 14 ].…”

“…The expansin gene family with many members can be divided into two major subfamilies, namely EXPA and EXPB subfamilies [ 15 ]. The various temporal and spatial expression patterns of expansin genes imply that they perform corresponding functions in different developmental stages [ 12 , 17 , 18 , 19 ]. Many studies have shown that EXPA subfamily plays complex and diverse functions in plant growth and development.…”

TaEXPB5 is responsible for male fertility in thermo-sensitive male-sterility wheat with Aegilops kotschyi cytoplasm

“…Expansion proteins are a type of cell wall binding protein that play an important role in the process of cell wall relaxation. Expansins usually have two typical domains, DPBB_1 and Pollen_allerg_1, and most of expansins have signal peptides (Liu et al . 2020).…”

Genome-Wide Identification and Expression Profiling of 2OGD Superfamily Genes from Three Brassica Plants

“…Phylogenetic analysis divided the species of Brassica into B. rapa, B. oleracea, and B. nigra lineages, which diverged approximately 8 MYA [41]. In Brassica plants, the interspecific cytogenetic relationship between important crops is well described with a "U" triangle, with two diploid species each (B. rapa (AA, n = 10), B. oleracea (CC, n = 9), and B. nigra (BB, n = 8)) forming a tetraploidy species (B. napus (AACC, n = 19), B. juncea (AABB, n = 18), or B. carinata (BBCC, n = 17)) [42,43]. With the complete genome sequencing of B. rapa, B. oleracea, and B. napus, great progress has been made in the study of the origin and evolution of Brassica plants.…”