Control of Potato Tuberization by GI and Proteins of the FT Family

• Autores: Eduard Cruz Oró
• Directores de la Tesis: Salomé Prat (dir. tes.)
• Lectura: En la Universidad Autónoma de Madrid ( España ) en 2017
• Idioma: inglés
• Tribunal Calificador de la Tesis: José María Romero Rodríguez (presid.), Miguel Redondo Nieto (secret.), José María Jiménez Gómez (voc.), Enrique Rojo de la Viesca (voc.), Federico Valverde Albacete (voc.)
• Enlaces
  • Tesis en acceso abierto en: Biblos-e Archivo
• Resumen

  • Potato is the fifth most important crop worldwide and is a staple food of critical relevance in terms of food security. The FT protein StSP6A is the main component of the “tuberigen” signal that is produced in the leaves and transported to the stolon to trigger tuber formation. In non-inductive LD photoperiodic conditions, StCOL1 inhibits tuberization by activating the FT protein StSP5G, engaged in repressing StSP6A transcription in the leaves. Identification of the earliness locus showed that expression of StCOL1 is repressed by StCDF1. Allelic variants of StCDF1 lacking the C-terminal StFKF1-interaction domain are not destabilized by the StFKF1-StGI complex and constitutively repress StCOL1.

    Here, we have demonstrated that StGI plays a critical role in the photoperiodic tuberization pathway and in the control of plant maturity by mediating destabilization of StCDF1. Transgenic potato plants silenced in StGI expression accumulate higher levels of the StCDF1 protein and show reduced levels of expression of the StCOL1, StCOL2 and StSP5G genes in LDs. Moreover, we show that silencing of StGI leads to activation of StSP6A and to changes in levels of expression of a large group of MADS-box factors, which act downstream of StSP6A in inducing tuberization and in conferring early maturity traits in potato. Furthermore, our studies revealed that, besides repressing StSP6A expression in the leaves, StSP5G regulates tuber shape likely by restricting cells undergoing differentiation, and its function is also required in mature tubers to preserve the shoot identity of tuber sprouts. Analysis of the gene regulatory network controlled by StSP5G demonstrates that this FT-like protein suppresses CK biosynthesis by repressing multiple isopentenyl transferase (IPT) genes, in addition to modulate a big set of MADS-box proteins in the leaves, tubers and in tuber sprouts. We have also demonstrated that warm temperatures inhibit tuberization by directly suppressing StSP6A expression in the leaves, while other regulators of the day-length pathway were not affected. We show that plants overexpressing StSP6A not only exhibit much higher tuber yields under warm temperatures but also show a reduced thermomorphogenic response. The transcriptomic analyses of these transgenic plants showed that StSP6A confers heat tolerance by repressing auxin, ethylene and jasmonic acid signalling, in addition to up-regulate photosynthesis and sugar export-related genes, thus evidencing an increased source capacity of leaves.

    Overall, these studies provide important insights regarding function of the StGI, StSP5G and StSP6A proteins in photoperiod and temperature-dependent control of tuber formation, and show that MADS-box transcription factors are downstream activation targets of StSP6A. We showed that StSP6A overexpression largely overcomes negative effects of temperature on tuber yield, quality, and dormancy. Hence, these findings provide a basis for improvement of potato heat tolerance by selecting cultivars where StSP6A expression is not reduced under warm temperatures.