Abstract
Plants have the capacity to adapt growth to changing environmental conditions. This implies the modulation of metabolism according to the availability of carbon (C). Particular interest in the response to the C availability is based on the increasing atmospheric levels of CO2. Several regulatory pathways that link the C status to growth have emerged. The extracellular EXO protein is essential for cell expansion and promotes shoot and root growth. Homologous proteins were identified in evolutionarily distant green plants. We show here that the EXO protein connects growth with C responses. The exo mutant displayed altered responses to exogenous sucrose supplemented to the growth medium. Impaired growth of the mutant in synthetic medium was associated with the accumulation of starch and anthocyanins, altered expression of sugar-responsive genes, and increased abscisic acid levels. Thus, EXO modulates several responses related to the C availability. Growth retardation on medium supplemented with 2-deoxy-glucose, mannose, and palatinose was similar to the wild type. Trehalose feeding stimulated root growth and shoot biomass production of exo plants whereas it inhibited growth of the wild type. The phenotypic features of the exo mutant suggest that apoplastic processes coordinate growth and C responses.
Highlights
A major challenge for plants is the coordination of supply and demand of carbohydrates and other carbon (C) compounds during the diurnal cycle and under changing environmental conditions
EXO ALTERS RESPONSES TO EXOGENOUS SUGARS To test growth in the presence of exogenous sugar, wild-type and exo plants were grown in half-concentrated Murashige and Skoog (MS) medium supplemented with different sucrose concentrations
A high sugar concentration (3% sucrose) caused a 19 and 53% reduction in shoot biomass growth of wild-type and exo plants, respectively, indicating that exo is more sensitive to high sugar levels in comparison to the wild type
Summary
A major challenge for plants is the coordination of supply and demand of carbohydrates and other carbon (C) compounds during the diurnal cycle and under changing environmental conditions. Plants developed regulatory pathways that allow matching C consumption and availability. These pathways imply both longdistance and cell type-specific signaling mechanisms (Rolland et al, 2006). As plants adapted to lower levels of ambient CO2 for millions of years, the current increase of atmospheric CO2 concentrations will affect crop yields via its effects on photosynthesis, plant metabolism, and water consumption (Leakey et al, 2009). The KIN10 (SnRK1.1) and KIN11 (SnRK1.2) kinases and the bZIP11 and ABI4 transcription factors play pivotal roles in the control of metabolism. Transcript levels of these genes were tested in wild-type and exo plants. Apart from TPS1, transcript levels were similar in wild-type and exo plants (Figure A3)
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