Abstract
Senescence in biofuel grasses is a critical issue because early senescence decreases potential biomass production by limiting aerial growth and development. 2-Dimensional, differential in-gel electrophoresis (2D-DIGE) followed by mass spectrometry of selected protein spots was used to evaluate differences between leaf proteomes of early (ES)- and late- senescing (LS) genotypes of Prairie cordgrass (ES/LS PCG) and switchgrass (ES/LS SG), just before and after senescence was initiated. Analysis of the manually filtered and statistically evaluated data indicated that 69 proteins were significantly differentially abundant across all comparisons, and a majority (41%) were associated with photosynthetic processes as determined by gene ontology analysis. Ten proteins were found in common between PCG and SG, and nine and 18 proteins were unique to PCG and SG respectively. Five of the 10 differentially abundant spots common to both species were increased in abundance, and five were decreased in abundance. Leaf proteomes of the LS genotypes of both grasses analyzed before senescence contained significantly higher abundances of a 14-3-3 like protein and a glutathione-S-transferase protein when compared to the ES genotypes, suggesting differential cellular metabolism in the LS vs. the ES genotypes. The higher abundance of 14-3-3 like proteins may be one factor that impacts the senescence process in both LS PCG and LS SG. Aconitase dehydratase was found in greater abundance in all four genotypes after the onset of senescence, consistent with literature reports from genetic and transcriptomic studies. A Rab protein of the Ras family of G proteins and an s-adenosylmethionine synthase were more abundant in ES PCG when compared with the LS PCG. In contrast, several proteins associated with photosynthesis and carbon assimilation were detected in greater abundance in LS PCG when compared to ES PCG, suggesting that a loss of these proteins potentially contributed to the ES phenotype in PCG. Overall, this study provides important data that can be utilized toward delaying senescence in both PCG and SG, and sets a foundational base for future improvement of perennial grass germplasm for greater aerial biomass productivity.
Highlights
Prairie cordgrass (PCG) and switchgrass (SG) are two warmseason C4 grasses that are widely adapted to North American climatic conditions and have great potential as feedstock for the lignocellulosic-based biofuels industry (Lee and Boe, 2005; Sarath et al, 2008; Gonzalez-Hernandez et al, 2009)
This study identified 69 statistically significant, differentially abundant proteins in PCG and SG genotypes contrasting in senescence, namely ES and late- senescing (LS), using 2-Dimensional, differential in-gel electrophoresis (2D-DIGE) followed by mass spectrometry of leaf samples collected just before and after onset of senescence
The goal was to begin a catalog of leaf proteins that could be indicators of either phenotype as a starting point for more proteomic and physiological studies to understand mechanisms impacting senescence in these two biofuel grasses
Summary
Prairie cordgrass (PCG) and switchgrass (SG) are two warmseason C4 grasses that are widely adapted to North American climatic conditions and have great potential as feedstock for the lignocellulosic-based biofuels industry (Lee and Boe, 2005; Sarath et al, 2008; Gonzalez-Hernandez et al, 2009). Leaf senescence is marked by the degradation of subcellular compartments, such as chloroplasts, and the remobilization of nutrients to other parts of the plants, such as seeds and underground rhizomes in the case of PCG and SG. The balance between oxidative stress and antioxidant activity plays a crucial role during senescence (Prochazkova et al, 2001). Senescence can be initiated by complex signals of age-specific factors in the genome and by temperature or day length in the case of seasonal senescence, and is often accompanied with increased ROS (reactive oxygen species) and oxidative stress (Jones et al, 2012; Palmer et al, 2015). During stress related and age specific senescence, these antioxidant pathways cannot overcome oxidative stress, leading to senescence rather than normal growth. Mitochondria are among the major sources of ROS and ROS-related stress signals during programmed cell death (Zhao and Xu, 2000; Fleury et al, 2002)
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