A20/AN1 zinc-finger proteins positively regulate major latex-like proteins, transporting factors toward dioxin-like compounds in Cucurbita pepo.

The Cucurbitaceae family accumulates dioxin-like compounds in its fruits. We previously showed that A20/AN1 zinc finger protein (ZFP) genes were highly expressed in the zucchini (Cucurbita pepo) subspecies pepo, which accumulates dioxin-like compounds at high concentrations. Transgenic tobacco (Nicotiana tabacum) plants overexpressing A20/AN1 ZFP genes show accumulation of dioxin-like compounds in their upper parts. However, the mechanisms underlying the accumulation of dioxin-like compounds regulated by the A20/AN1 ZFPs remain unclear. Here, we show that A20/AN1 ZFPs positively regulate the expression of the major latex-like protein (MLP) and its homolog genes in N. tabacum and C. pepo. MLPs are involved in the transport of dioxin-like compounds from the roots to the upper parts of C. pepo. Overexpression of A20/AN1 ZFP genes in N. tabacum leads to the upregulation of pathogenesis-related protein class-10 genes with the binding ability toward dioxin-like compounds. Our results demonstrated that A20/AN1 ZFPs upregulate MLP and its homolog genes in N. tabacum and C. pepo, resulting in the accumulation of dioxin-like compounds.

Zinc finger protein genes from Cucurbita pepo are promising tools for conferring non-Cucurbitaceae plants with ability to accumulate persistent organic pollutants.

Some cultivars of cucumbers, melons, pumpkins, and zucchini, which are members of the Cucurbitaceae family, are uniquely subject to contamination by hydrophobic pollutants such as the organohalogen insecticides DDT. However, the molecular mechanisms for the accumulation of these pollutants in cucurbits have not been determined. Here, cDNA subtraction analysis of Cucurbita pepo cultivars that are low and high accumulators of hydrophobic contaminants revealed that a gene for zinc finger proteins (ZFPs) are preferentially expressed in high accumulators. The cloned CpZFP genes were classified into 2 types: (1) the PBG type, which were expressed in C. pepo cultivars Patty Green, Black Beauty, and Gold Rush, and (2) the BG type, which were expressed in Black Beauty and Gold Rush. Expression of these CpZFP genes in transgenic tobacco plants carrying an aryl hydrocarbon receptor-based inducible gene expression system significantly induced ß-glucuronidase activity when the plants were treated with a polychlorinated biphenyl (PCB) compound, indicating that highly hydrophobic PCBs accumulated in the plants. In transgenic tobacco plants carrying CpZFPs, accumulation of dioxins and dioxin-like compounds increased in their aerial parts when they were cultivated in the dioxin-contaminated soil. In summary, we propose that addition of CpZFP genes is a promising tool for conferring noncucurbits with the ability to accumulate hydrophobic contaminants.