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Transcriptome profiling after reducing source-to-sink ratio in tomato plants reveals alterations in source leaf activity

ABSTRACT: Responses to altered source–sink balance have been characterized in many crops at the physiological level, but the underlying genetic and molecular mechanisms are largely unknown. Detailed transcriptional profiling was performed in partially defoliated and shaded tomato plants to explore the effect of reduced source-to-sink ratio on molecular changes in the remaining source leaves. Transcription profiles of the remaining leaves 48 h after partial defoliation or partial shading were compared to leaves of control plants. Common significantly altered genes in the two treatments were assumed to be related to the reduced source-to-sink ratio. Sets of major genes in the abscisic acid, ethylene and gibberellin signal-transduction pathways were downregulated by both treatments. On the other hand, genes encoding cytokinin biosynthesis were upregulated. Most genes coding for transcription factors were also downregulated, especially those related to biotic and abiotic stress responses. Perhaps the most pronounced effect of reduced source-to-sink ratio was related to genes involved in the regulation of photosynthetic activity. Numerous genes coding for light-harvesting proteins, as well as those encoding plastocyanin, ferredoxin and ferredoxin NADP+ oxidoreductase were upregulated. Direct spectrophotometric analyses showed higher maximal potential activity of photosystem I with reduced source-to-sink ratio. As expected, the increased capacity for photosynthetic activity was associated with upregulation of almost all genes coding for the Calvin–Benson cycle and those encoding ATP biosynthesis in the mitochondria. Numerous transcriptional changes were observed 48 h after reducing source-to-sink ratio. Major genes in the photosynthetic-activity pathways were upregulated, whereas those in the pathways of defense mechanisms and responses to stress were downregulated. Genes involved in leaf senescence were also downregulated, suggesting that in addition to increased photosynthetic activity, the remaining leaves undergo a process of rejuvenation.

ORGANISM(S): Solanum lycopersicum

PROVIDER: GSE201432 | GEO | 2023/08/01

REPOSITORIES: GEO

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Project description:In C4 sugarcane (Saccharum spp. hybrids), photosynthetic activity has been shown to be regulated by the demand for carbon from sink tissues. There is evidence, from other plant species, that sink-limitation of photosynthesis is facilitated by sugar-signaling mechanisms in the leaf that affect photosynthesis through regulation of gene expression. In this work, we manipulated leaf sugar levels by cold-girdling leaves (5oC) for 80 h to examine the mechanisms whereby leaf sugar accumulation affects photosynthetic activity and assess whether signaling mechanisms reported for other species operate in sugarcane. During this time, sucrose and hexose concentrations above the girdle increased by 77% and 81%, respectively. Conversely, leaf photosynthetic activity (A) and electron transport rates (ETR) decreased by 66% and 54%, respectively. Quantitative expression profiling by means of an Affymetrix GeneChip Sugarcane Genome Array was used to identify genes responsive to cold-girdling (56 h). A number of genes (74) involved in primary and secondary metabolic pathways were identified as being differentially expressed. Decreased expression of genes related to photosynthesis and increased expression of genes involved in assimilate partitioning, cell wall synthesis, phosphate metabolism and stress were observed. Furthermore four probe sets homologous to trehalose 6-phosphate phosphatase (TPP; EC 5.3.1.1) and trehalose 6-phosphate synthase (TPS; EC 2.4.1.15) were up- and down-regulated, respectively, indicating a possible role for trehalose 6-phosphate (T6P) as a putative sugar-sensor in sugarcane leaves. Twelve month-old field grown Saccharum spp. (L.) hybrid cv. N19 (N19) cultivated at Mount Edgecombe, KwaZulu-Natal (SASRI) were used in the study, which was conducted in November, 2006. Plants were grown on a 5 x 15 m plot located on a north-east facing slope with a gradient of ca. 10o. Cold-girdles were attached to sugarcane leaves (n=4) for a period of 56 h prior to harvest. The girdle consisted of 0.75 cm (diameter) soft plastic tubing, firmly clamped around each leaf, approximately 30 cm from the leaf base. Cooled water maintained at 5oC was then pumped through the tubing using a Grant LTD6G cooling bath (Grant Instruments, Barrington, Cambridge, UK). At harvest, leaf samples were immediately frozen in liquid nitrogen (–196oC) and subsequently milled in an A11 Basic Analysis Mill (IKA, Staufen, Germany). Ground leaf tissue was stored at –80oC in 50 ml centrifuge tubes prior to analysis.

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Transcriptome profiling after reducing source-to-sink ratio in tomato plants reveals alterations in source leaf activity

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