Abstract
The COBRA-like (COBL) genes play key roles in cell anisotropic expansion and the orientation of microfibrils. Mutations in these genes cause the brittle stem and induce pathogen responsive phenotypes in Arabidopsis and several crop plants. In this study, an in silico genome-wide analysis was performed to identify the COBL family members in Brassica. We identified 44, 20 and 23 COBL genes in B. napus and its diploid progenitor species B. rapa and B. oleracea, respectively. All the predicted COBL genes were phylogenetically clustered into two groups: the AtCOB group and the AtCOBL7 group. The conserved chromosome locations of COBLs in Arabidopsis and Brassica, together with clustering, indicated that the expansion of the COBL gene family in B. napus was primarily attributable to whole-genome triplication. Among the BnaCOBLs, 22 contained all the conserved motifs and derived from 9 of 12 subgroups. RNA-seq analysis was used to determine the tissue preferential expression patterns of various subgroups. BnaCOBL9, BnaCOBL35 and BnaCOBL41 were highly expressed in stem with high-breaking resistance, which implies these AtCOB subgroup members may be involved in stem development and stem breaking resistance of rapeseed. Our results of this study may help to elucidate the molecular properties of the COBRA gene family and provide informative clues for high stem-breaking resistance studies.
Highlights
Plant morphogenesis is dependent on the regulation of cell division and expansion
We identified 44 BnaCOBLs, 20 BraCOBLs, and 23 BolCOBLs in the genomes of the allotetraploid Brassica napus and its diploid progenitor species B. rapa and B. oleracea, respectively
Brassica evolved from a Brassiceae lineage-specific whole genome triplication (WGT) [19] after diverged from a common ancestor with Arabidopsis about 20 million years ago [50, 51]
Summary
Plant morphogenesis is dependent on the regulation of cell division and expansion. Most plant cells grow anisotropically through internal and isotropic turgor pressure yield from cell walls [1]. The plant cell wall is a dynamic, complex fibrillar network. After the plant cell expands to its final shape and the primary cell wall is formed, the secondary cell wall is formed and thickens between the primary cell wall and plasma membrane [2, 3]. The COBRA gene, which encodes a glycosylphosphatidylinositol (GPI) anchored protein [1, 4, 5], regulates microfibril deposition on the cell surface at the rapid elongation stage to guarantee a normal anisotropic expansion of the cell wall during plant morphogenesis.
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