Sugar/osmoticum levels modulate differential abscisic acid-independent expression of two stress-responsive sucrose synthase genes in Arabidopsis

Abstract

Sucrose synthase (Sus) is a key enzyme of sucrose metabolism. Two Sus-encoding genes (Sus1 and Sus2) from Arabidopsis thaliana were found to be profoundly and differentially regulated in leaves exposed to environmental stresses (cold stress, drought or O2 deficiency). Transcript levels of Sus1 increased on exposure to cold and drought, whereas Sus2 mRNA was induced specifically by O2 deficiency. Both cold and drought exposures induced the accumulation of soluble sugars and caused a decrease in leaf osmotic potential, whereas O2 deficiency was characterized by a nearly complete depletion in sugars. Feeding abscisic acid (ABA) to detached leaves or subjecting Arabidopsis ABA-deficient mutants to cold stress conditions had no effect on the expression profiles of Sus1 or Sus2, whereas feeding metabolizable sugars (sucrose or glucose) or non-metabolizable osmotica [poly(ethylene glycol), sorbitol or mannitol] mimicked the effects of osmotic stress on Sus1 expression in detached leaves. By using various sucrose/mannitol solutions, we demonstrated that Sus1 was up-regulated by a decrease in leaf osmotic potential rather than an increase in sucrose concentration itself. We suggest that Sus1 expression is regulated via an ABA-independent signal transduction pathway that is related to the perception of a decrease in leaf osmotic potential during stresses. In contrast, the expression of Sus2 was independent of sugar/osmoticum effects, suggesting the involvement of a signal transduction mechanism distinct from that regulating Sus1 expression. The differential stress-responsive regulation of Sus genes in leaves might represent part of a general cellular response to the allocation of carbohydrates during acclimation processes.

The low oxygen, oxidative and osmotic stress responses synergistically act through the ethylene response factorVIIgenesRAP2.12,RAP2.2andRAP2.3

“…To determine whether the enhanced osmotic sensitivity of rap2 mutants correlated with changes in the activities of RAP2‐responsive marker genes, 10‐day‐old wild type and rap2 mutant seedlings were transferred to medium supplemented with 300 m m mannitol. ADH1 and SUS1 transcript levels were tested after 0, 3 and 9 h of osmotic stress (Figure e; Dejardin et al ., ; Papdi et al ., ). Whereas the wild type and single rap2 mutants showed comparable ADH1 expression, it was 40% lower in the rap2.12‐2 rap2.3‐1 double mutant after 9 h of mannitol treatment.…”

Functional analysis of sucrose phosphate synthase (SPS) and sucrose synthase (SS) in sugarcane (Saccharum) cultivars

“…SS resides in the cytoplasm of photosynthetic and non‐photosynthetic tissues (Geigenberger & Stitt 1993; Nolte & Koch 1993). SS isoforms exhibit different spatial and temporal expression patterns and are differentially regulated at transcriptional and translational levels (Dejardin et al. 1999).…”

Activation tagging of a gene for a protein with novel class of CCT‐domain activates expression of a subset of sugar‐inducible genes in Arabidopsis thaliana

“…, 1995). By contrast, the level of mRNA for SUS2 , which encodes sucrose synthase 2 (Dejardin et al. , 1999), was similar between the two lines.…”