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Research Project: Soybean Seed Improvement Through Quantitative Analysis of Phenotypic Diversity in Response to Environmental Fluctuations

Location: Plant Genetics Research

Title: Transcriptional response to petiole heat girdling in cassava

Author
item ZHANG, YANG - Institute Of Tropical Bioscience And Biotechnology, Chinese Academy Of Tropical Agricultural Scienc
item DING, ZEHONG - Institute Of Tropical Bioscience And Biotechnology, Chinese Academy Of Tropical Agricultural Scienc
item MA, FANGFANG - Danforth Plant Science Center
item DEEPIKA CHAUHAN, RAJ - Danforth Plant Science Center
item Allen, Douglas - Doug
item BRUTNELL, TOM - Danforth Plant Science Center
item WANG, WENQUAN - Institute Of Tropical Bioscience And Biotechnology, Chinese Academy Of Tropical Agricultural Scienc
item PENG, MING - Institute Of Tropical Bioscience And Biotechnology, Chinese Academy Of Tropical Agricultural Scienc
item LI, PINGHUA - Institute Of Tropical Bioscience And Biotechnology, Chinese Academy Of Tropical Agricultural Scienc

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2015
Publication Date: 2/12/2015
Publication URL: http://handle.nal.usda.gov/10113/61126
Citation: Zhang, Y., Ding, Z., Ma, F., Chauhan, R.D., Allen, D.K., Brutnell, T., Wang, W., Peng, M., Li, P. 2015. Transcriptional response to petiole heat girdling in cassava. Scientific Reports. 5:8414.

Interpretive Summary: The capability of agriculture to feed a growing world population in the future will depend on improving crop yield and composition that enhances the production of food, feed and fiber for society. Plants assimilate carbon dioxide in leaves through photosynthesis and convert it into biomass. During the day plant leaves export fixed carbon primarily as sugars in the form of sucrose and accumulate starch that is turned over at night to sustain metabolism when it is dark. Therefore the leaves are a "source" tissue that supplies nutrients to other parts of the plant. The other parts, like seeds and tubers are a "sink" tissue in that they utilize the nutrients to produce the oil, protein and storage carbohydrates. The relationship between source and sink tissues in the plant is complex and difficult to understand but is important because it establishes yield. Techniques that can alter the partitioning of carbon, can perturb the balance of source and sink and are important to study. One technique involves heating the stems of plants, called heat girdling, which blocks the export of metabolites and alters carbohydrate metabolism. The effects of heat girdling on photosynthetic metabolism were explored at the gene transcript and metabolic levels. As a result of the treatment at the end of the day, the accumulated starch was not efficiently converted and exported to other parts of the plant. The disruption in starch remobilization impacted multiple photosynthetic parameters and repressed related metabolic pathways in leaves leading to a complex response and indicating that source to sink relationships are controlled by many factors. These studies are important because the combination of gene expression data and metabolite analysis can improve our understanding of biomass production and provide candidates for genetic engineering aimed at enhancing crop yield.

Technical Abstract: The heat-girdling technique, which is known to inhibit photoassimilate translocation, was performed on the petiole of cassava leaves at the end of the light cycle to inhibit starch remobilization during the night. The inhibition of starch remobilization caused significant starch accumulation at the beginning of the light cycle, which inhibited photosynthesis and affected intracellular sugar levels. Changes in photosynthesis and sugar levels may influence the transcriptome, and the genes that respond to these changes may be important for understanding homeostasis regulation between source supply and sink demand. Based on RNA-Seq comparison of leaves with or without heat girdling treatment, we observed significantly decreased expression of genes related to photosynthesis, N-metabolism and chlorophyll biosynthesis. However, expression of genes TCA and mitochondria electron transport, as well as flavonoid biosynthetic pathways, were induced significantly. Changes in primary and secondary metabolism, as well as sugar and light signaling, may increase our understanding of the relationship between source and sink and provide target genes for future bio-engineering to further improve cassava yield.