The potato is one of the most important vegetable and food crops in the United States and the highest gross value crop in Israel. Physiological aging of seed tubers during storage is a serious problem because it affects the number of plant stems and determines daughter-tuber sizes. The number of stems produced by the seed tuber is determined by chronological age, genotype, and growth and storage conditions. Storage temperature conditions impact Israeli farmers who import about 30,000 tons of seed tubers annually because they do not know how to prevent the over-sprouting and branching in cold storage of seed tubers harvested in the summer and held until the following winter. Growing certain potato cultivars in the cold, northern United States presents the opposite challenge: long dormancy and a low number of stems growing from the seed tuber. Moreover, the potato industry usually prefers specific tuber sizes that can be targeted by modifying the number of stems.
A BARD-funded American Israeli collaboration between Dr. Dani Eshel from ARO, Volcani Center in Israel and Dr. Jiming Jian from Michigan State University’s department of plant biology are studying potato physiology and genetics postharvest sweetening of potato seed tubers and effects on their yield performance. The bilateral collaboration was based on the synergistic activities of the two laboratories in the fields of potato physiology and genetics. This research project provides new insight on the understanding of dormancy and sprouting shape of seed tubers. The investigators’ working hypothesis was that the parenchyma sweetening induced by cold storage conditions is a key factor controlling stem number and branching.
The Israeli researcher, Dr. Dani Eshel, has a great deal of experience and knowledge in physiological and molecular aspects of postharvest biology of potato tubers. The potato CRISPR/CAs9 techniques being used in the proposal are extensively used in his laboratory and shared with the US lab led by Prof. Jiang. The U.S. investigator, Prof. Jiang, is a potato geneticist with much experience and knowledge in potato genetics, genomics and breeding. The VInv-silenced and overexpressing lines to be used in this study have been developed and characterized in his laboratory. Thus, reagents, protocols and samples were and will be shared between the U.S. and Israel, as has been done successfully in the last three years. It is clear this study involves an active and true collaboration between the two teams, as either group could not perform it alone.
The research objectives were: 1) to determine the role of sugars vs. phytohormones originating from tuber parenchyma in signaling etiolated stems to branch, using grafting followed by stem-sap analysis; and 2) to determine whether VInv-overexpressing lines produce less stems in response to branching inducers; They also wished to edit the VInv gene, using CRISPR/Cas9, to modify stem number in non-transgenic commercial cultivars, based on Jiang's discovery that cold-induced expression of VInv is regulated by its second intron. Eventually, based on the knowledge gained from this project, they hope to develop target molecules and CRISPR-modified commercial cultivars with a controllable number of tuber-produced stems and subsequent yield.
The combined expertise revealed new aspects of potato sweetening during cold storage and exposure to heat, and novel genome-editing protocols for improved seed-tuber storage and control of sprouting shape. Identification of key mechanisms associated with sweetening is also relevant for the development of new strategies or treatments to alleviate sugar accumulation postharvest. The byproducts of this research may mitigate health concerns by allowing the development of potato cultivars that have reduced contents of the acrylamide precursors, glucose and fructose, in cold-stored tubers.