Identification Of Key Cis-elements In Promoter Of Arabidopsis SLO Gene

As a signaling molecule, sugar can cooperate with plant hormones (ethylene, abscisic acid). Recently, genetics and molecular biology studies on sugar signaling mutant in Arabidopsis have revealed that there are interactions and connections between sugar and hormone signaling pathways. Besides the changes in response to sugar signaling, the phenotypes of these mutants are similar to ABA/ethylene biosynthesis mutants.We identified an Arabidopsis recessive mutant slo with delay in various developmental stages, such as leaf expansion, flowering and senescence. This mutant also exhibits less sensitivity to ACC, the ethylene biosynthesis precursor, and ethylene regarding their inhibitory effects on leaf expansion, partial resistance to ethylene and hypersensitivity to abscisic acid (ABA) and sugar as well. We isolated SLO by map-based cloning and proved the mutated gene encodes a pentatricopeptide repeat (PPR) protein. Several lines of evidence have shown that SLO is involved in sugar, ABA and ethylene signaling.To characterize the spatial and temporal expression patterns of SLO and identify the possible cis-elements in the promoter region responsible for sugar/hormone responses, we obtained a series of deleted promoter fragments, fused with a reporter gene encoding β-glucuronidase (GUS), then introduced into Col wild-type plants through Agrobacterium-mediated transformation. The seedlings of multiple independent transgenic lines were grown on half MS media supplemented with different signaling components including sugar. We found GUS-staining was readily visible in root tips and shoot apexes of 5-days-dark grown seedlings transformed with full length promoter-GUS fusion gene; sugar enhanced GUS expression, whereas ACC and ABA attenuated GUS expression. When the etiolated seedlings were treated with both ACC and sugar, GUS expression was lower than that treated with sugar alone but higher than treated with ACC alone. However, the 40-day-old adult plants showed strong GUS-staining in stems, and filaments and stamens of flowers as well, with exception of flower buds, leaves and roots. We found the sugar-responsive cis-elements are located in - 549bp ~ - 287bp region of SLO promoter by GUS-staining.The results indicate the sugar responsive cis-elements of SLO are located in -549bp-287bp ofthe promoter, and may play important roles in sugar-induced gene expression. The SLO expression is controlled by sugar and ethylene, and ethylene can repress sugar-induced SLO expression. The strong GUS expression in stems, and filaments and stamens of flowers in adult plants implicates SLO expression...