Laboratory of Plant Physiological Ecology (LAFIECO), Department of Botany, Institute of Biosciences, University of São Paulo, Rua do Matão 277, São Paulo, SP, Brazil.
Laboratory of Plant Physiological Ecology (LAFIECO), Department of Botany, Institute of Biosciences, University of São Paulo, Rua do Matão 277, São Paulo, SP, Brazil
J Exp Bot. 2015 Jul;66(14):4133-43. doi: 10.1093/jxb/erv171. Epub 2015 Apr 28.
Cell-wall recalcitrance to hydrolysis still represents one of the major bottlenecks for second-generation bioethanol production. This occurs despite the development of pre-treatments, the prospect of new enzymes, and the production of transgenic plants with less-recalcitrant cell walls. Recalcitrance, which is the intrinsic resistance to breakdown imposed by polymer assembly, is the result of inherent limitations in its three domains. These consist of: (i) porosity, associated with a pectin matrix impairing trafficking through the wall; (ii) the glycomic code, which refers to the fine-structural emergent complexity of cell-wall polymers that are unique to cells, tissues, and species; and (iii) cellulose crystallinity, which refers to the organization in micro- and/or macrofibrils. One way to circumvent recalcitrance could be by following cell-wall hydrolysis strategies underlying plant endogenous mechanisms that are optimized to precisely modify cell walls in planta. Thus, the cell-wall degradation that occurs during fruit ripening, abscission, storage cell-wall mobilization, and aerenchyma formation are reviewed in order to highlight how plants deal with recalcitrance and which are the routes to couple prospective enzymes and cocktail designs with cell-wall features. The manipulation of key enzyme levels in planta can help achieving biologically pre-treated walls (i.e. less recalcitrant) before plants are harvested for bioethanol production. This may be helpful in decreasing the costs associated with producing bioethanol from biomass.
细胞壁对水解的顽固性仍然是第二代生物乙醇生产的主要瓶颈之一。尽管已经开发了预处理方法、新酶的前景以及生产细胞壁顽固性降低的转基因植物，但仍然存在这种情况。顽固性是聚合物组装所施加的固有降解阻力，是其三个领域固有局限性的结果。这些包括：(i) 与果胶基质相关的孔隙率，阻碍了通过细胞壁的运输；(ii) 糖基码，指的是细胞壁聚合物的精细结构突现复杂性，这些复杂性是细胞、组织和物种所特有的；和 (iii) 纤维素结晶度，指的是在微观和/或宏观纤维中的组织。一种规避顽固性的方法可能是遵循植物内源性机制下的细胞壁水解策略，这些策略经过优化，可以在植物体内精确修饰细胞壁。因此，本文综述了果实成熟、脱落、贮藏细胞壁动员和通气组织形成过程中细胞壁的降解，以突出植物如何应对顽固性，以及如何将有前景的酶和鸡尾酒设计与细胞壁特征结合起来。在收获用于生物乙醇生产之前，在植物体内操纵关键酶的水平可以帮助实现生物预处理的细胞壁（即降低顽固性）。这可能有助于降低从生物质生产生物乙醇相关的成本。
