Characterization of Mutants in Arabidopsis Showing Increased Sugar-Specific Gene Expression, Growth, and Developmental Responses

Abstract

Sugars such as sucrose serve dual functions as transported carbohydrates in vascular plants and as signal molecules that regulate gene expression and plant development. Sugar-mediated signals indicate carbohydrate availability and regulate metabolism by co-coordinating sugar production and mobilization with sugar usage and storage. Analysis of mutants with altered responses to sucrose and glucose has shown that signaling pathways mediated by sugars and abscisic acid interact to regulate seedling development and gene expression. Using a novel screen for sugar-response mutants based on the activity of a luciferase reporter gene under the control of the sugar-inducible promoter of the ApL3 gene, we have isolated high sugar-response (hsr) mutants that exhibit elevated luciferase activity and ApL3 expression in response to low sugar concentrations. Our characterization of these hsr mutants suggests that they affect the regulation of sugar-induced and sugar-repressed processes controlling gene expression, growth, and development in Arabidopsis. In contrast to some other sugar-response mutants, they do not exhibit altered responses to ethylene or abscisic acid, suggesting that the hsr mutants may have a specifically increased sensitivity to sugars. Further characterization of the hsr mutants will lead to greater understanding of regulatory pathways involved in metabolite signaling.Sugars such as Glc and Suc regulate many important cellular processes in plants (for review, see Rolland et al., 2002;Rook and Bevan, 2003). The expression of genes involved in photosynthate accumulation, mobilization, and storage is regulated by Glc and Suc (Koch, 1996), and by lightmediated (Neff et al., 2000) and circadian clockmediated (Harmer et al., 2000) signaling mechanisms. This regulatory network serves to integrate the synthesis and use of carbohydrates in different tissues and organs in response to environmental changes and in response to the availability of other nutrients such as nitrogen (Coruzzi and Bush, 2001). The outputs of this regulatory network maintain an optimal dynamic carbohydrate status. For example, in conditions of high carbohydrate demand and if sufficient light energy is available, the regulatory network increases production and mobilization of photosynthate by increasing expression of genes involved in photosynthesis (Koch, 1996), and conversely, when photosynthate is not immediately required, genes involved in starch synthesis (Rook et al., 2001) are activated to maintain a balance between photosynthate supply, demand, and storage. Transport functions respond to photosynthate availability by modulation of Suc transporter gene expression and protein levels (Chiou and Bush, 1998;Vaughn et al., 2002) to integrate carbohydrate sink demand with carbohydrate source production and export.Significant progress is being made in identifying the mechanisms controlling carbohydrate status in plants. Genetic screens in Arabidopsis have identified mutants affecting growth, development, and gene expression responses to Glc, ...

Sugar Sensing and Signaling

“…Both sugar insensitive and hypersensitive mutants are also obtained based on the sugar-inducible expression of a β-amylase gene (Mita et al, 1997a;Mita et al, 1997b). Other screens include the use of the sugar inducible patatin promoter in front of a GUS reporter gene (rsr, reduced sucrose response mutants) (Martin et al, 1997) or the ApL3 promoter in front of a luciferase reporter gene (hsr, high sugar response mutants) (Baier et al, 2004) (Table I).…”

EXORDIUM-LIKE1 Promotes Growth during Low Carbon Availability in Arabidopsis

“…Arabidopsis seedlings can develop leaf-and flowerlike organs in the dark, but skotomorphogenesis critically depends on the sugar availability (Roldán et al, 1999;Baier et al, 2004;Li et al, 2007). Similar to photomorphogenic development, skotomorphogenic development of exl1 was identical with the wild type when grown in medium supplemented with 1% Suc or 1% Glc.…”

“…The molecular basis of this result is unknown and could be manifold. Altered sugar transport, enhanced sugar responses, and cell wall changes were demonstrated to accelerate leaf and internodium formation in darkness (Baier et al, 2004;Li et al, 2007).…”

“…4 and 5). Skotomorphogenesis is a sensitive indicator of the effects of sugar on development, because C availability determines activity of the shoot apical meristem (Roldán et al, 1999;Baier et al, 2004). Dark development of exl1 was accelerated in medium supplemented with 0.15% Glc or Suc (Fig.…”

The effect of sugars in relation to methyl jasmonate on anthocyanin formation in the roots of Kalanchoe blossfeldiana (Poelln.)

“…Sugars are important factors in the accumulation of anthocyanins, especially in plants cultured in vitro and in germinating plants [4,5]. Different sugars have been found to enhance anthocyanin accumulation in carrot [6], udo [7], and strawberry [8] grown in nutrient media.…”