Abstract
The Sucrose non-Fermenting Related Kinase 1 (SnRK1) proteins have been linked to regulation of energy and stress signaling in eukaryotes. In plants, there is a small SnRK1 gene family. While the SnRK1.1 gene has been well studied, the role other SnRK1 isoforms play in energy or stress signaling is less well understood. We used promoter:GUS analysis and found SnRK1.1 is broadly expressed, while SnRK1.2 is spatially restricted. SnRK1.2 is expressed most abundantly in hydathodes, at the base of leaf primordia, and in vascular tissues within both shoots and roots. We examined the impact that sugars have on SnRK1 gene expression and found that trehalose induces SnRK1.2 expression. Given that the SnRK1.1 and SnRK1.2 proteins are very similar at the amino acid level, we sought to address whether SnRK1.2 is capable of re-programming growth and development as has been seen previously with SnRK1.1 overexpression. While gain-of-function transgenic plants overexpressing two different isoforms of SnRK1.1 flower late as seen previously in other SnRK1.1 overexpressors, SnRK1.2 overexpressors flower early. In addition, SnRK1.2 overexpressors have increased leaf size and rosette diameter during early development, which is the opposite of SnRK1.1 overexpressors. We also investigated whether SnRK1.2 was localized to similar subcellular compartments as SnRK1.1, and found that both accumulate in the nucleus and cytoplasm in transient expression assays. In addition, we found SnRK1.1 accumulates in small puncta that appear after a mechanical wounding stress. Together, these data suggest key differences in regulation of the SnRK1.1 and SnRK1.2 genes in plants, and highlights differences overexpression of each gene has on the development of Arabidopsis.
Highlights
The Sucrose non-Fermenting Related Kinase 1 (SnRK1) family of proteins has been linked to regulation of energy metabolism and stress signaling in diverse types of eukaryotes (Halford and Hey, 2009; Coello et al, 2011; Tsai and Gazzarrini, 2014)
DEVELOPMENTAL REGULATION OF SnRK1.1 AND SnRK1.2 EXPRESSION To explore the role SnRK1 may play in plant growth and development, we examined the spatial and temporal regulation of expression of the SnRK1.1 and SnRK1.2 genes
Soil-grown plants were analyzed and indicate that SnRK1.1 continues to be broadly expressed in the shoot (Figure 1G), whereas, activity of the SnRK1.2 promoter is restricted to the base of newly developing leaves and hydathodes (Figure 1H)
Summary
The Sucrose non-Fermenting Related Kinase 1 (SnRK1) family of proteins has been linked to regulation of energy metabolism and stress signaling in diverse types of eukaryotes (Halford and Hey, 2009; Coello et al, 2011; Tsai and Gazzarrini, 2014). Overexpression of the SnRK1.1 gene re-programs metabolism such that flowering and senescence of mature plants is delayed (Baena-Gonzalez et al, 2007). The delay in flowering and senescence effectively lengthens the lifespan of the plant, most likely through the combined direct protein phosphorylation of SnRK1 substrates, regulation of transcription in the nucleus (Baena-Gonzalez et al, 2007), and post-transcriptional regulation of target genes (Confraria et al, 2014). Analysis of SnRK1 genetic mutants in Arabidopsis showed that SnRK1.1 and SnRK1.2 genes have partially redundant functions, www.frontiersin.org
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