Modifying lignin composition and xylan O-acetylation induces changes in cell wall composition, extractability, and digestibility.

Background: Lignin and xylan are important determinants of a cell wall structure and lignocellulosic biomass digestibility. Genetic manipulations that individually modify either lignin or xylan structure improve polysaccharide digestibility. However, the effects of their simultaneous modifications have not been explored in a similar context. Here, we generated combinatorial cell wall mutants and studied the consequences on plant cell wall properties, biotic stress responses and plant cell wall integrity. Results Arabidopsis plant co-harbouring mutation in ferulate 5-hydroxylase ( fah1-2 ) and overexpressing Aspergillus niger acetyl xylan esterase (35S: An AXE1) transgenic were generated and displayed normal growth attributes with intact xylem architecture. This fah1-2 /35S: An AXE1 crossed named as h ype r G lignin and hyp o ac etylated (HrGHypAc) line. The HrGHypAc plants showed increased crystalline cellulose content with enhanced digestibility after chemical and enzymatic pre-treatment. Moreover, both parents and HrGHypAc without and after pre-treating with glucuronyl esterase and alpha glucuronidase exhibited an increase in xylose release after xylanase digestion as compared to wild-type. The de-pectinated fraction in HrGHypAc displayed elevated levels of xylan and cellulose content. Furthermore, the transcriptomic analysis revealed differential expression in cell wall biosynthetic, transcription factors and wall-associated kinases genes implying the role of lignin and xylan modification on cellular processes. Conclusions Simultaneous modification in xylan and lignin improve cellulose content with enhanced saccharification efficiency. These modifications loosen cell wall complexity and hence resulted in enhanced xylose release with or without treatment after xylanase digestion. This study also revealed that the disruption of xylan and lignin structure is possible without compromising either growth and development or defense responses against Pseudomonas syringae infection.