A BELL1-Like Gene of Potato Is Light Activated and Wound Inducible

Abstract

BELL1-like transcription factors interact with their protein partners from the KNOTTED1 family to bind to target genes and regulate numerous developmental and metabolic processes. In potato (Solanum tuberosum), the BELL1 transcription factor StBEL5 and its protein partner POTH1 regulate tuber formation by affecting hormone levels. Overexpression of StBEL5 in transgenic lines produces plants that consistently exhibit enhanced tuber formation, and the mRNA of this gene moves through phloem cells in a long-distance signaling pathway regulated by photoperiod. Whereas photoperiod mediates the movement of StBEL5 RNA, activation of transcription of the StBEL5 gene in leaves is regulated by white light, regardless of photoperiod or light intensity. Illumination with either red or blue light induces the StBEL5 promoter, whereas far-red light had no effect. As expected, the StBEL5 promoter harbors numerous conventional light-responsive cis-acting elements like GT1, GATA, and AT1 motifs. Deletion constructs were analyzed to determine what sequences are involved in light activation. Transcriptional activity was also mediated by wounding on stems, insect predation on leaves, and photoperiod in stolons. These results demonstrate that StBEL5 gene activity in the leaf is correlated with wavelengths optimal for photosynthesis. The number of factors that affect the StBEL5 promoter supports the premise that the BELL1-like genes play a role in a wide range of functions.

Accumulation of BEL1-like transcripts in solanaceous species

“…Based on the wound-induction pattern previously described (Chatterjee et al 2007) and verified in the current study, it is plausible that BEL5-like genes function as a phloem defense signal responsive to mechanical or insect damage. A BEL1-like gene from rice, OsBIHD1, was identified that functions in disease resistance and pathogen defense (Luo et al 2005).…”

“…The lower section of midveins contains, in order, starting from the lamina, xylem, phloem, and collenchyma tissue (Esau 1977). Consistent with these results, in potato, the foliar midveins are the primary source of StBEL5 promoter activity (Chatterjee et al 2007). …”

“…Previous studies demonstrated that the promoter of StBEL5 was activated in response to wounding in stems but not leaves (Chatterjee et al 2007). To determine if other solanaceous species exhibited a similar pattern of expression, wound induction for both leaves and stems was examined for S. etuberosum and S. palustre.…”

The Multiple Signals That Control Tuber Formation

“…As discussed earlier, StBEL5 autoregulates its own gene in stolon tips, where promoter activity is induced by SD (Chatterjee et al, 2007;Lin et al, 2013). Deletion of one of the TTGAC motifs present in the StBEL5 upstream sequence essentially eliminated its promoter activity in stolons and new tubers (Lin et al, 2013).…”

“…2). This autoregulation was verified through site mutagenesis in an upstream sequence of the StBEL5 gene (Lin et al, 2013) and helps to explain the SD-induced activity of the StBEL5 promoter in stolons growing in the dark (Chatterjee et al, 2007).…”