Sucrose transport in the phloem: integrating root responses to phosphorus starvation

Abstract

Sugars in plants, derived from photosynthesis, act as substrates for energy metabolism and the biosynthesis of complex carbohydrates, providing sink tissues with the necessary resources to grow and to develop. In addition, sugars can act as secondary messengers, with the ability to regulate plant growth and development in response to biotic and abiotic stresses. Sugar-signalling networks have the ability to regulate directly the expression of genes and to interact with other signalling pathways. Photosynthate is primarily transported to sink tissues as sucrose via the phloem. Under phosphorus (P) starvation, plants accumulate sugars and starch in their leaves. Increased loading of sucrose to the phloem under P starvation not only functions to relocate carbon resources to the roots, which increases their size relative to the shoot, but also has the potential to initiate sugar-signalling cascades that alter the expression of genes involved in optimizing root biochemistry to acquire soil phosphorus through increased expression and activity of inorganic phosphate transporters, the secretion of acid phosphatases and organic acids to release P from the soil, and the optimization of internal P use. This review looks at the evidence for the involvement of phloem sucrose in co-ordinating plant responses to P starvation at both the transcriptional and physiological levels.

Light-dependent activation of phosphoenolpyruvate carboxylase by reversible phosphorylation in cluster roots of white lupin plants: diurnal control in response to photosynthate supply

“…Transcriptional expression of various Pi-responsive genes in white lupin CRs (including that encoding the dominant PEPC isozyme LaPEPC3 (PEPC isozyme-3 from L. albus)) also increased in the light and decreased in the dark, suggesting that light-driven changes in the supply of photosynthate (sucrose) from the leaves to the CRs regulated expression of these genes in the latter (Liu et al, 2005;Cheng et al, 2011Cheng et al, , 2014. The data support the view that shoot carbohydrate supply plays a crucial role in orchestrating root metabolic responses to Pi limitation, including white lupin CRs (Liu et al, 2005;Hammond and White, 2008;Cheng et al, 2011Cheng et al, , 2014.…”

“…translocated from source leaves is part of a systemic signalling system that leads to Pi deficiency-induced alterations in root morphology and metabolism in white lupin and other plant species, including arabidopsis (Liu et al, 2005;Hammond and White, 2008;Cheng et al, 2011Cheng et al, , 2014Wang et al, 2014). Here, we have established a novel mechanistic link between reversible in vivo PEPC phosphorylation and the concentrations of sucrose and its signalling molecule Tre6P (Yadav et al, 2014), while correlating this interesting phenomenon with the diurnal control of organic anion exudation and Pi uptake by CRs of ÀPi white lupin plants (Watt and Evans, 1999;Hocking and Jeffery, 2004;Liu et al, 2005;Cheng et al, 2014).…”

mRNA-Seq Reveals a Comprehensive Transcriptome Profile of Rice under Phosphate Stress

“…This may be associated with the tightly controlled mechanisms that allow the coordination of Pi homeostasis with carbon status and photosynthesis (Wissuwa et al 2005). Sugars generated in the shoots and transported through the phloem are involved in establishing a physiological, biochemical, and molecular response to −P stress in plants (Hammond and White 2008). Sucrose phosphatase encoding transcript (Os01t0376700) was upregulated in root at late -P stress whereas sucrose synthase encoding transcripts (Os06t0194900 and Os03t0401300) were downregulated in shoot and root at late-P stress and root at middle ++P stress.…”

Impact of soil tillage on the robustness of the genetic component of variation in phosphorus (P) use efficiency in barley (Hordeum vulgare L.)

“…Many plant species are adapted to P-deficiency and have developed a range of mechanisms that enhance their ability to acquire P from soil (White et al 2005;Vance et al, 2003). These include modifications to root structure (Hammond & White, 2008), the formation of symbioses with mycorrhizae (Smith & Read, 1997), and the production of root exudates such as organic anions (Ryan et al, 2001) and phosphatase enzymes (Tadano et al, 1993;George et al, 2002). P-use efficiency is therefore a multi-mechanistic trait whose genetic control is likely to be greatly affected by environment (George et al 2008) Although genotypic variation in P-use efficiency of cereals is reported (Batten & Khan, 1987;Jones et al, 1989;Jones et al, 1992;Gahoonia & Nielsen, 1996;Manske et al, 2000;Osborne & Rengel, 2002a,b;Wang et al, 2005), few studies have investigated this variation in contrasting environmental conditions and the robustness of the genetic component of variation is rarely tested.…”