Chitinase-like (CTL) and cellulose synthase (CESA) gene expression in gelatinous-type cellulosic walls of flax (Linum usitatissimum L.) bast fibers.

Natalia Mokshina,Tatyana Gorshkova,Michael K Deyholos,Olga A Zabotina

doi:10.1371/journal.pone.0097949

Natalia Mokshina, Tatyana Gorshkova + Show 2 more

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https://doi.org/10.1371/journal.pone.0097949

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Abstract

Plant chitinases (EC 3.2.1.14) and chitinase-like (CTL) proteins have diverse functions including cell wall biosynthesis and disease resistance. We analyzed the expression of 34 chitinase and chitinase-like genes of flax (collectively referred to as LusCTLs), belonging to glycoside hydrolase family 19 (GH19). Analysis of the transcript expression patterns of LusCTLs in the stem and other tissues identified three transcripts (LusCTL19, LusCTL20, LusCTL21) that were highly enriched in developing bast fibers, which form cellulose-rich gelatinous-type cell walls. The same three genes had low relative expression in tissues with primary cell walls and in xylem, which forms a xylan type of secondary cell wall. Phylogenetic analysis of the LusCTLs identified a flax-specific sub-group that was not represented in any of other genomes queried. To provide further context for the gene expression analysis, we also conducted phylogenetic and expression analysis of the cellulose synthase (CESA) family genes of flax, and found that expression of secondary wall-type LusCESAs (LusCESA4, LusCESA7 and LusCESA8) was correlated with the expression of two LusCTLs (LusCTL1, LusCTL2) that were the most highly enriched in xylem. The expression of LusCTL19, LusCTL20, and LusCTL21 was not correlated with that of any CESA subgroup. These results defined a distinct type of CTLs that may have novel functions specific to the development of the gelatinous (G-type) cellulosic walls.

Highlights

Flax (Linum usitatissimum L.) phloem fibers are a valuable industrial feedstock and are a convenient model system for studying secondary cell wall formation
LusCTL Phylogenetic Characterization We searched within the flax genome assembly for predicted genes with homology to Pfam domain PF00182, which is characteristic of chitinases of the glycosyl hydrolase family 19 (GH 19) family [31,38]
LusCTL1 and LusCTL2 were so named because they encoded proteins that were most similar to CTL1 and CTL2, respectively, which have been characterized in other species (e.g. A. thaliana [14] and G. hirsutum [10]) (Table 2)

Summary

Introduction

Flax (Linum usitatissimum L.) phloem fibers are a valuable industrial feedstock and are a convenient model system for studying secondary cell wall formation. The mechanical properties of bast fibers are largely dependent on the composition of their secondary walls. Bast fibers have gelatinous-type walls, which are rich in cellulose (up to 90%) and lack detectable xylan and lignin. Either phloem or xylem (of either primary or secondary origin) can produce gelatinous fibers in various organs including stems, roots, tendrils, vines, and peduncles [1,2]. The mechanisms of gelatinous cell wall development in these fibers remain largely unclear. Some genes implicated in gelatinous cell wall development have been identified. A role for b-galactosidases in G-type wall development has been demonstrated functionally [8]

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