Sucrose non-fermenting kinase 1 (SnRK1) coordinates metabolic and hormonal signals during pea cotyledon growth and differentiation

Abstract

SUMMARYSeed development passes through developmental phases such as cell division, differentiation and maturation: each have specific metabolic demands. The ubiquitous sucrose non-fermenting-like kinase (SnRK1) coordinates and adjusts physiological and metabolic demands with growth. In protoplast assays sucrose deprivation and hormone supplementation, such as with auxin and abscisic acid (ABA), stimulate SnRK1-promoter activity. This indicates regulation by nutrients: hormonal crosstalk under conditions of nutrient demand and cell proliferation. SnRK1-repressed pea (Pisum sativum) embryos show lower cytokinin levels and deregulation of cotyledonary establishment and growth, together with downregulated gene expression related to cell proliferation, meristem maintenance and differentiation, leaf formation, and polarity. This suggests that at early stages of seed development SnRK1 regulates coordinated cotyledon emergence and growth via cytokinin-mediated auxin transport and/or distribution. Decreased ABA levels and reduced gene expression, involved in ABA-mediated seed maturation and response to sugars, indicate that SnRK1 is required for ABA synthesis and/or signal transduction at an early stage. Metabolic profiling of SnRK1-repressed embryos revealed lower levels of most organic and amino acids. In contrast, levels of sugars and glycolytic intermediates were higher or unchanged, indicating decreased carbon partitioning into subsequent pathways such as the tricarbonic acid cycle and amino acid biosynthesis. It is hypothesized that SnRK1 mediates the responses to sugar signals required for early cotyledon establishment and patterning. As a result, later maturation and storage activity are strongly impaired. Changes observed in SnRK1-repressed pea seeds provide a framework for how SnRK1 communicates nutrient and hormonal signals from auxins, cytokinins and ABA to control metabolism and development.

Wheat Grain Development Is Characterized by Remarkable Trehalose 6-Phosphate Accumulation Pregrain Filling: Tissue Distribution and Relationship to SNF1-Related Protein Kinase1 Activity

“…In marked contrast at 17 DAA high concentrations of T6P were confined to the endosperm with very low amounts in embryos and pericarp. T6P levels in wheat embryos (0.6 nmol g 21 FW) are of a similar order to those in pea embryos (2 nmol g 21 FW; Radchuk et al, 2010) and more than 70-fold lower than amounts measured in endosperm and maternal tissues. SnRK1 was again active in all tissues, but it is likely that SnRK1 activity in pericarp and embryo is not inhibited by T6P at 17 DAA.…”

“…All published data on amounts of T6P in plants are from Arabidopsis seedlings and leaf material with other data from pea embryos (Radchuk et al, 2010). But there has been no detailed and comprehensive analysis of T6P in the harvested parts of any major crop such as wheat.…”

“…Interestingly, it has been proposed that SnRK1 mediates responses to sugar signals required for early cotyledon establishment and patterning (Radchuk et al, 2010). To our knowledge, Radchuk et al (2010) presented the first T6P measurements in a seed tissue in the embryos of pea (Pisum sativum). The significance of these data relative to the regulation of SnRK1 is not known, however.…”

“…SnRK1 plays an important role in the regulation of metabolism and development in crop sinks such as potato (Solanum tuberosum) tubers (McKibbin et al, 2006) and in seeds of legumes (Weber et al, 2005;Radchuk et al, 2010). Interestingly, it has been proposed that SnRK1 mediates responses to sugar signals required for early cotyledon establishment and patterning (Radchuk et al, 2010). To our knowledge, Radchuk et al (2010) presented the first T6P measurements in a seed tissue in the embryos of pea (Pisum sativum).…”

“…Of the little that has been documented on the trehalose pathway in wheat, active enzymes are present in roots and shoots (El-Bashiti et al, 2005) and transcripts in roots (Mohammadi et al, 2007) and the transcripts of TPS and TPP enzymes in wheat grain (Weichert et al, 2010). SnRK1 plays an important role in the regulation of metabolism and development in crop sinks such as potato (Solanum tuberosum) tubers (McKibbin et al, 2006) and in seeds of legumes (Weber et al, 2005;Radchuk et al, 2010). Interestingly, it has been proposed that SnRK1 mediates responses to sugar signals required for early cotyledon establishment and patterning (Radchuk et al, 2010).…”