Abstract
Metabolic enzymes have been found to play roles in plant development. Sucrose synthase (SUS) is one of the two enzyme families involved in sucrose cleavage in plants. In tomato, six SUS genes have been found. We generated transgenic tomato plants with RNAi suppression of SlSUS1, SlSUS3 and SlSUS4 genes. Independent transgenic lines with RNAi suppression of more than one SUS gene exhibited morphological effects on their cotyledons and leaf structure, but there were no significant effects on their carbohydrate levels, demonstrating that SUS has a developmental function, in addition to its metabolic function. Shoot apices of the transgenic lines showed elevated expression of JAGGED (JAG) and the auxin transporter PIN1. In a PIN1-GFP fusion reporter/SUS-RNAi hybrid, PIN1-GFP patterns were altered in developing leaves (as compared to control plants), indicating that SlSUS suppression alters auxin signaling. These results suggest possible roles for SUS in the regulation of plant growth and leaf morphology, in association with the auxin-signaling pathway.
Highlights
In plants, sugars function as metabolic resources and structural components, and as regulators of various processes related to growth and development at all stages of life, from germination to senescence [1,2,3,4,5,6,7,8]
Three sucrose synthases (SUS) genes, SlSUS1 SlSUS3 and SlSUS4, were identified before the publication of the tomato genome sequence and, following the release of the tomato genome sequence, we identified three additional SUS genes
The three new tomato SUS genes were reported by Qin et al [12] and named SlSUS5, SlSUS6 and SlSUS7, bringing the total number of SUS genes in tomato to six, as in Arabidopsis
Summary
Sugars function as metabolic resources and structural components, and as regulators of various processes related to growth and development at all stages of life, from germination to senescence [1,2,3,4,5,6,7,8]. Sucrose is transported through the phloem to sink tissues, where it must be cleaved before it can enter metabolic pathways. Sucrose cleavage in sink and source tissues is carried out by members of two separate enzyme families, invertases that cleave sucrose into glucose and fructose and sucrose synthases (SUS) that cleave sucrose into fructose and UDP-glucose. Both families are comprised of multiple isozymes. At least five invertases and six sucrose synthase genes have been described in tomato [9,10,11,12,13].
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