Proteomics reveals an increase in the abundance of glycolytic and ethanolic fermentation enzymes in developing sugarcane culms during sucrose accumulation

Sugarcane is an economically important crop contributing to the world’s sugar and ethanol production with 80% and 40%, respectively. In recent years, the growing demands for sugar and ethanol production has prompted the necessity to increase sugarcane productivity through conventional breeding programs. However, sugarcane breeders have encountered several difficulties to raise productivity, mainly due to its complex genetics. Sugarcane has a polyploidy genome, with many varieties being aneuploidy. Today, the majority of the planted sugarcane cultivars are complex hybrids derived mainly from crosses between Saccharum officinarum and S. spontaneum. Therefore, proteomics can provide some insight into deciphering gene regulation and changes in carbon metabolism and sucrose accumulation in the culms at different stages of plant development. The aim of this work was to compare the quantitative changes of proteins in sugarcane culms, during plant growth and sucrose accumulation. Total proteins were isolated from both, juvenile and maturing internodes at three stages of plant development. Label free shotgun proteomics was used for protein profiling and quantification. The internodes 5 (I5) and 9 (I9) of 4, 7 and 10 month-old-plants (4M, 7M and 10M, respectively) were harvested and used for proteomic analyses. To mimic field conditions of sucrose accumulation during sugarcane maturation, we stopped watering 10M plants for 10 days. An average of 1130 proteins, unique and differentially expressed across all ages were identified and quantified. Proteins were categorized within 27 functional groups, related to biological process. The patterns of expression for some categories, such as cellular amino acids, metabolic processes, secondary metabolic processes and translation were down-regulated in the immature internode (I5-10M), while up-regulated in the mature I9-10M. We observed an increase in the abundance of several enzymes of the glycolytic pathway and isoforms of alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PDC), in the juvenile stages of development of I9. These changes in enzymes contents indicates that at the early stages of internode development, hypoxia is increasing the glycolytic and ethanolic fermentation pathways, in order to supply ATP for plant growth and NAD+ for mitochondrial respiration, which might be impaired by the low oxygen availability inside the culm.

甘蔗是具有重要经济价值的作物，分别贡献了全球80%的蔗糖产量与40%的乙醇产量。近年来，全球对蔗糖与乙醇产能的需求持续增长，推动了通过传统育种手段提升甘蔗生产力的迫切需求。然而，甘蔗育种工作者在提升生产力方面遭遇了诸多难题，这主要源于其复杂的遗传背景：甘蔗拥有多倍体基因组，多数栽培品种为非整倍体。当前，主流种植的甘蔗栽培品种多为复杂杂交种，主要由普通甘蔗（Saccharum officinarum）与甜根子草（S. spontaneum）杂交选育而来。因此，蛋白质组学（proteomics）可为解析甘蔗茎秆在不同发育阶段的基因调控、碳代谢变化以及蔗糖积累机制提供研究视角。本研究旨在探究甘蔗茎秆在植株生长与蔗糖积累过程中蛋白质的定量变化规律。总蛋白质分别从三个发育阶段的幼龄节间与成熟节间中提取，采用无标记鸟枪法蛋白质组学（Label free shotgun proteomics）进行蛋白质谱分析与定量。本研究采集了4、7、10月龄植株（分别记为4M、7M和10M）的第5节间（I5）与第9节间（I9），用于后续蛋白质组学分析。为模拟甘蔗成熟阶段蔗糖积累的田间环境，研究人员对10月龄植株实施了为期10天的控水处理。本研究共鉴定并定量了平均1130种各发育阶段特异且差异表达的蛋白质。这些蛋白质被划分为27个与生物过程相关的功能类群。部分功能类别的表达模式存在显著差异：如细胞氨基酸代谢、次级代谢以及翻译相关过程在未成熟节间（I5-10M）中表达下调，而在成熟节间（I9-10M）中表达上调。研究人员还观察到，在I9节间的幼龄发育阶段，糖酵解通路的多种酶类以及乙醇脱氢酶（ADH）、丙酮酸脱羧酶（PDC）的同工酶丰度显著升高。上述酶含量的变化表明，在节间发育的早期阶段，低氧环境会激活糖酵解与乙醇发酵通路，以满足植株生长所需的ATP供应，并为线粒体呼吸提供NAD+——而茎秆内部的低氧条件可能会削弱线粒体呼吸功能。