Editors' ChoicePlant biology

Tomato Tubers

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Science Signaling  02 Jul 2013:
Vol. 6, Issue 282, pp. ec148
DOI: 10.1126/scisignal.2004470

Despite producing very different edible products, tomato and potato are closely related species. In potato, the tips of juvenile basal axial shoots called stolons swell to produce edible tubers that not only store nutrients but also are reproductive structures. Under conditions of stress or after application of sucrose and exogenous hormones, potato plants develop small tubers along the main shoot (aerial minitubers), indicating that all stem cells—not just those in the basal shoots—have the potential to form tubers and that this potential is normally suppressed. Eviatar-Ribak et al. report that ectopic expression of tomato LONELY GUY 1 (TLOG1), which encodes an enzyme that catalyzes the formation of the active form of the hormone cytokinin (CK) from an inactive precursor, resulted in the formation of aerial minitubers in tomato. Endogenous TLOG1 was expressed dynamically in vegetative, reproductive, and axial meristems, whereas ectopic ubiquitous and continuous expression of TLOG1 resulted in the formation of aerial minitubers from the first few nodes (axial meristems) on the primary shoot of juvenile plants. Starch granules accumulated in the minitubers, which were morphologically similar to potato aerial minitubers, and transcriptomic analysis suggested that they were metabolically similar as well. Genetic interaction experiments suggested that minituber formation resulted from an imbalance in CK and auxin signaling. Whereas ectopic TLOG1 activated juvenile axial meristems to produce the minitubers, it suppressed the development of structures derived from floral, apical, and leaf meristems. In many plant species, the microRNA miR156 regulates developmental timing by promoting maintenance of the juvenile state. Simultaneous ectopic ubiquitous expression of TLOG1 and miR156 resulted in the formation of aerial minitubers at every axial node on both primary and secondary shoots, indicating that increased CK signaling can only induce tuber formation in juvenile meristems. Direct application of CK to juvenile axial meristems activated these nodes to produce stems and leaves but failed to induce the formation of minitubers. Thus, subtle changes in the local hormonal balance can dramatically affect the identity of organs formed by activated meristems.

T. Eviatar-Ribak, A. Shalit-Kaneh, L. Chappell-Maor, Z. Amsellem, Y. Eshed, E. Lifschitz, A cytokinin-activating enzyme promotes tuber formation in tomato. Curr. Biol. 23, 1057–1064 (2013). [PubMed]