Identification of genes involved in early endodormancy break in potato tubers

Abstract

The growth and harvest of potato tubers for agricultural purposes is important both in Canada and worldwide, and the agronomic importance of this crop is steadily growing. A major issue affecting the storage and transport of raw potatoes is the precocious sprouting of tuber shoot apical meristems (SAMs), which is a result of tuber emergence from endodormancy. Current methods of potato storage that prolong endodormancy require either large cold storage facilities, or the use of growth suppressing chemicals. In this study, tuber SAM growth and the molecular mechanisms underlying endodormancy emergence were investigated to better understand the physiological processes involved. During emergence, SAM length increased and was paralleled by increased DNA synthesis as early as 7 weeks post-harvest, suggesting endodormancy release before or at this time. The genes WUS and STM, which are involved with meristem maintenance and growth, were expressed as early as 7 weeks post-harvest. By 11 weeks post-harvest, WUS was expressed at significantly higher levels (~5 fold) than in endodormant tuber meristems. PKL and CUCl, genes thought to be involved in the activation of WUS and STM, increased in expression at 11 weeks, then decreased to significantly lower levels at 15 weeks. Expression of other dormancy enforcing genes such as ABI5 and DHN also significantly decreased during emergence. Suppressive subtractive hybridization identified other genes that were down-regulated in non-dormant tissues. These included BPSl, thought to be involved with synthesis of a mobile signal, whose mRNA levels were significantly lower at 15 and 19 weeks, and RCEl, a member of the SCF [superscript TIR1] complex involved with auxin regulated protein degradation, which had significantly lower mRNA levels after 19 weeks. Additionally, the stress tolerance gene DREB2a showed a slight increase in expression (-20%) at 11 weeks post-harvest but then decreased, and at 19 weeks post-harvest it was significantly lower (-40%). Expression of the cell cycle dependent gene cyc07 and a WD-Repeat gene were characterized as well. The molecular mechanisms investigated contribute to the understanding of tuber endodormancy, which may lead to better cultivation and storage practices.