(691d) Advanced Characterization of Poplar Variants for Understanding Plant Cell Wall Recalcitrance

Certain poplar variants have been identified to carry a rare natural mutation associated with EPSP (5-enolpyruvylshikimate-3-phosphate) synthase biosynthesis gene that lowers their lignin content. Our recent work has shown that the rare variant (BESC-35) and low lignin comparator (GW-11012), had reduced klason lignin content of 18%. On the other hand, a high lignin comparator (BESC-316), had a klason lignin content of 23%. Rare variant and low lignin comparator were some of the highest-ranking plants and high lignin comparator was one of the low-ranking plants, with respect to sugar yield from pretreatment and enzymatic hydrolysis combined. In this study, differences in cell wall properties of these three high or low sugar yielding poplar plants were investigated using SANS, AFM, TEM, NMR, GPC, and compositional analysis. SANS suggested that the rare variant had looser packing of cellulose microfibrils. AFM using PeakForce quantitative nanomechanical property mapping (QNM) found that the high lignin comparator had significantly higher tip-surface adhesion than rare variant or low lignin comparator possibly due to its higher lignin content. Moreover, lower syringyl/guaiacyl (S/G) ratio of high lignin comparator (2.58) agreed with the assertion that lower S/G ratio in poplar can negatively affect sugar yield. However, despite the rare variant and low lignin comparator being low in lignin content and high sugar yielding plants, their S/G ratios of 4.27 and 3.13 were widely different. AFM and TEM suggested high heterogeneity in cell walls of high lignin comparator. Overall, these findings provide new insights into differences in poplar plants associated with recalcitrance.