Phylogenetic and Functional Analysis of CesA Genes in Cotton

Background: Cotton (Gossypium hirsutum) is widely distributed all over the world, and improving the quality of its fiber is one of the most important tasks in cotton breeding. Cotton fibers are primarily composed of cellulose, which is synthesized and regulated by cellulose synthase (CesAs). But the molecular mechanism of CesA genes in cotton was unclear. Results: In this study, the phylogenetic history and purifying selection of CesA genes were investigated along with their functions. CesA3 and CesA6 are the two largest subgroups in G. arboreum, comprising 52.8% of the whole CesA family. These two CesA subgroups were then chosen for further research, and the results showed that they are highly differentiated in dicot groups. The two subgroups were also discriminated with the use of a Ka/Ks analysis. This indicated that they may play an important role in fiber development based on their unique phylogenetic status. Functional studies were subsequently conducted using the most purified genes (Gohir.A08G144300.1 in CesA3 subgroup). The silencing of Gohir.A08G144300.1 visibly inhibits the growth of cotton fiber, showing that it is critical for the growth of cotton fibers. Conclusions: The results presented here a target gene Gohir.A08G144300.1 based on the analysis of CesA gene members, and it is found that this gene was crucial to the growth of cotton fibers. This study provides more information for the understanding of the molecular mechanism of cotton fiber development.

Analysis of public RNA-seq data in studies of flax fiber biogenesis

In this work we used publicly available raw RNA-seq data to elucidate mechanisms of flax fiber biogenesis by measuring expression of cell-wall related genes (cellulose synthase, cellulose synthase-like and chitinase-like genes) in stem of flax (Linum usitatissimum cv. Bethune). Using public RNA-sequence data we have quantified and characterised the expression of the specific cell-wall genes in the top, middle and bottom parts of the Bethune flax stem. The most prominent findings are: Secondary cell-wall cellulose synthase (CesA) genes are expressed differentially in phloem and xylem in all parts of Bethune stem, in contrast with primary cell-wall cellulose synthase genes. Total expression level of cellulose synthase-like (Csl) genes is tissue invariant (although, CslG and CslE are differentially expressed) and smaller than the total expression of cellulose synthase genes. The CslD2D3 subgroup dominates total expression of CslD genes in both xylem and phloem. Expression levels of all expressed chitinase-like (Ctl) genes are tissue dependent in all parts of stem. Total expression level of chitinase-like genes is much higher than expression of cellulose synthase and cellulose synthase-like genes in both tissues.

Cellulosic fibres of flax recruit both primary and secondary cell wall cellulose synthases during deposition of thick tertiary cell walls and in the course of graviresponse

Cellulose synthesising complex consists of cellulose synthase (CESA) subunits encoded by a multigene family; different sets of CESA genes are known to be expressed during primary and secondary cell wall formation. We examined the expression of LusCESAs in flax (Linum usitatissimum L.) cellulosic fibres at various stages of development and in the course of graviresponse by means of RNA-Seq and quantitative PCR. Transcripts for both primary and secondary cell wall-related CESAs were abundant in fibres depositing highly cellulosic tertiary cell walls. Gravistimulation of flax plants temporally increased the abundance of CESA transcripts, specifically in phloem fibres located at the pulling stem side. Construction of coexpression networks for LusCESAs revealed that both primary and secondary cell wall-related CESAs were involved in the joint coexpression group in fibres depositing tertiary cell walls, as distinct from other tissues, where these genes were within separate groups. The obtained data suggest that fibres depositing tertiary cell walls have a specific mechanism of cellulose biosynthesis and a specific way of its regulation.