Hodgson-Kratky K, Papa G, Rodriguez A, Stavila V, Simmons B, Botha F, Furtado A, Henry R
1Queensland Alliance for Agriculture and Food Innovation, University of Queensland, Brisbane, QLD 4072 Australia.
3Joint BioEnergy Institute, Emeryville, CA 94608 USA.
Biotechnol Biofuels. 2019 Oct 17;12:247. doi: 10.1186/s13068-019-1588-3. eCollection 2019.
Lignocellulosic biomass is recognized as a promising renewable feedstock for the production of biofuels. However, current methods for converting biomass into fermentable sugars are considered too expensive and inefficient due to the recalcitrance of the secondary cell wall. Biomass composition can be modified to create varieties that are efficiently broken down to release cell wall sugars. This study focused on identifying the key biomass components influencing plant cell wall recalcitrance that can be targeted for selection in sugarcane, an important and abundant source of biomass.
Biomass composition and the amount of glucan converted into glucose after saccharification were measured in leaf and culm tissues from seven sugarcane genotypes varying in fiber composition after no pretreatment and dilute acid, hydrothermal and ionic liquid pretreatments. In extractives-free sugarcane leaf and culm tissue, glucan, xylan, acid-insoluble lignin (AIL) and acid-soluble lignin (ASL) ranged from 20 to 32%, 15% to 21%, 14% to 20% and 2% to 4%, respectively. The ratio of syringyl (S) to guaiacyl (G) content in the lignin ranged from 1.5 to 2.2 in the culm and from 0.65 to 1.1 in the leaf. Hydrothermal and dilute acid pretreatments predominantly reduced xylan content, while the ionic liquid (IL) pretreatment targeted AIL reduction. The amount of glucan converted into glucose after 26 h of pre-saccharification was highest after IL pretreatment (42% in culm and 63.5% in leaf) compared to the other pretreatments. Additionally, glucan conversion in leaf tissues was approximately 1.5-fold of that in culm tissues. Percent glucan conversion varied between genotypes but there was no genotype that was superior to all others across the pretreatment groups. Path analysis revealed that S/G ratio, AIL and xylan had the strongest negative associations with percent glucan conversion, while ASL and glucan content had strong positive influences.
To improve saccharification efficiency of lignocellulosic biomass, breeders should focus on reducing S/G ratio, xylan and AIL content and increasing ASL and glucan content. This will be key for the development of sugarcane varieties for bioenergy uses.
木质纤维素生物质被认为是生产生物燃料的一种有前景的可再生原料。然而，由于次生细胞壁的顽固性，目前将生物质转化为可发酵糖的方法被认为过于昂贵且效率低下。可以对生物质组成进行改良，以培育出能够有效分解从而释放细胞壁糖的品种。本研究着重于确定影响植物细胞壁顽固性的关键生物质成分，这些成分可作为甘蔗（一种重要且丰富的生物质来源）选择的目标。
对七种纤维组成不同的甘蔗基因型在未预处理以及经过稀酸、水热和离子液体预处理后的叶片和茎杆组织，测定了生物质组成以及糖化后转化为葡萄糖的葡聚糖量。在去除提取物的甘蔗叶片和茎杆组织中，葡聚糖、木聚糖、酸不溶性木质素（AIL）和酸溶性木质素（ASL）的含量分别在20%至32%、15%至21%、14%至20%和2%至4%之间。木质素中紫丁香基（S）与愈创木基（G）含量的比率在茎杆中为1.5至2.2，在叶片中为0.65至1.1。水热和稀酸预处理主要降低木聚糖含量，而离子液体（IL）预处理的目标是降低AIL含量。与其他预处理相比，预糖化26小时后转化为葡萄糖的葡聚糖量在IL预处理后最高（茎杆中为42%，叶片中为63.5%）。此外，叶片组织中的葡聚糖转化率约为茎杆组织的1.5倍。葡聚糖转化率在不同基因型之间有所差异，但在所有预处理组中没有一个基因型优于其他所有基因型。通径分析表明，S/G比率、AIL和木聚糖与葡聚糖转化率的负相关性最强，而ASL和葡聚糖含量有很强的正影响。
为提高木质纤维素生物质的糖化效率，育种者应专注于降低S/G比率、木聚糖和AIL含量，并增加ASL和葡聚糖含量。这对于开发用于生物能源的甘蔗品种至关重要。
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