Pectin biosynthesis pathways are adapted to higher rhamnogalacturonan formation in lignocellulosic jute (Corchorus spp.)

Pectin and lignin are two enigmatic macromolecular components of cell wall, which are spatially and temporally deposited during plant growth. While the former is important for primary growth, the latter accumulates during secondary growth. With the evolution of land plants, the structural complexity of pectin increased to protect cell walls against the intrusion of pectinolytic pathogens besides offering multiple choices for its interaction with lignin. We reconstructed pectin biosynthesis pathways in an annual lignocellulosic bast fibre-producing crop jute (Corchorus spp.) from hypocotyl transcriptomes and identified 27 isoforms of 17 genes and 12 isoforms of galacturonosyltransferase involved in nucleotide-sugar interconversion and pectin polymerization, respectively. Salvage pathways were found to be functional for replenishing nucleotide sugars in jute hypocotyls. Phylogenetic analyses revealed that the genes of pectin biosynthesis pathways are well conserved across taxa. For significant upregulation of the rhamnose biosynthesis gene (RHM1), we traced its evolution, identified its two-domain protein structure proposed to have been evolved from charophycean green algae and generated a structural model explaining its functional conservation. Retting of jute stem with pectinolytic bacteria showed that pectin complexity and its interaction with lignin play crucial roles in resisting cell wall deconstruction that may have accrued from increased rhamnogalacturonan biosynthesis.