Abstract
The molecular basis behind shade tolerance in plants is not fully understood. Previously, we have shown that a connection may exist between shade tolerance and dwarfism, however, the mechanism connecting these phenotypes is not well understood. In order to clarify this connection, we analyzed the transcriptome of a previously identified shade-tolerant mutant of perennial ryegrass (Lolium perenne L.) called shadow-1. shadow-1 mutant plants are dwarf, and are significantly tolerant to shade in a number of environments compared to wild-type controls. In this study, we treated shadow-1 and wild-type plants with 95% shade for 2 weeks and compared the transcriptomes of these shade-treated individuals with both genotypes exposed to full light. We identified 2,200 differentially expressed genes (DEGs) (1,096 up-regulated and 1,104 down-regulated) in shadow-1 mutants, compared to wild type, following exposure to shade stress. Of these DEGs, 329 were unique to shadow-1 plants kept under shade and were not found in any other comparisons that we made. We found 2,245 DEGs (1,153 up-regulated and 1,092 down-regulated) in shadow-1 plants, compared to wild-type, under light, with 485 DEGs unique to shadow-1 plants under light. We examined the expression of gibberellin (GA) biosynthesis genes and found that they were down-regulated in shadow-1 plants compared to wild type, notably gibberellin 20 oxidase (GA20ox), which was down-regulated to 3.3% (96.7% reduction) of the wild-type expression level under shade conditions. One GA response gene, lipid transfer protein 3 (LTP3), was also down-regulated to 41.5% in shadow-1 plants under shade conditions when compared to the expression level in the wild type. These data provide valuable insight into a role that GA plays in dwarfism and shade tolerance, as exemplified by shadow-1 plants, and could serve as a guide for plant breeders interested in developing new cultivars with either of these traits.
Highlights
Perennial ryegrass (Lolium perenne L.) is one of the most widely cultivated cool-season turfgrass species in the world (Jiang and Huang, 2001; Chen J. et al, 2016)
We compared differential gene expression between lightgrown shadow-1, shade-treated shadow-1, light-grown wildtype, and shade-treated wild type, in a four-way comparison (Figure 4C). This four-way comparison exposed 329 differentially expressed genes (DEGs) that were unique to shadow-1 when compared to wild-type under shade conditions, and 485 DEGs that were unique to shadow-1 if compared to wild type under light conditions
We analyzed the transcriptomes of the shadetolerant perennial ryegrass mutant shadow-1 kept under light and shade, to explore the mechanisms behind both dwarfism and shade-tolerance in these plants
Summary
Perennial ryegrass (Lolium perenne L.) is one of the most widely cultivated cool-season turfgrass species in the world (Jiang and Huang, 2001; Chen J. et al, 2016). While perennial ryegrass is incorporated into many seed mixtures due to its positive traits, it is seldom grown by itself because of its sensitivity to a number of environmental stresses (Gardner and Taylor, 2002; Tegg and Lane, 2004). Perennial ryegrass struggles to grow in overly shady environments, exhibiting shade avoidance response (SAR). This condition is characterized by weak growth, overly elongated leaves, and chlorosis (Franklin and Whitelam, 2005). Shade has been shown to reduce the production of grains, such as kernels in maize, as well as seeds, as seen in Brassica rapa (Page et al, 2010; Procko et al, 2014)
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