Genome-wide identification and characterization of major latex-like protein genes responsible for crop contamination in Cucurbita pepo.

BACKGROUND: Zucchini plants (Cucurbita pepo) accumulate persistent organic pollutants (POPs) at high concentrations in their aerial parts, and major latex-like proteins (MLPs) play crucial roles in their accumulation. MLPs bind to POPs in root cells, MLP-POP complexes are then translocated into xylem vessels, and POPs are transported to the aerial parts. We previously identified three CpMLP genes (MLP-PG1, MLP-GR1, and MLP-GR3) as transporting factors for POPs; however, other studies have shown that the genomes of several plant species contain more than 10 MLP genes, thus, further MLP genes responsible for POP accumulation may have been overlooked. METHODS AND RESULTS: Here, we investigated the number of CpMLP genes by performing a hidden Markov model search against the C. pepo genome database and characterized their effects on POP accumulation by performing the expression analysis in the organs and in silico structural analysis. The C. pepo genome contained 21 CpMLP genes, and several CpMLP genes, including MLP-PG1 and MLP-GR3, were highly expressed in roots. 3D structural prediction showed that all examined CpMLPs contained a cavity with a hydrophobic region, which facilitated binding to POPs. CONCLUSIONS: The present study provides insights regarding CpMLP genes responsible for POP accumulation.

Major latex-like proteins show pH dependency in their binding to hydrophobic organic pollutants.

The Cucurbitaceae family accumulates hydrophobic organic pollutants in its aerial parts at high concentrations. Major latex-like proteins (MLPs) were identified in zucchini (Cucurbita pepo) as a transporting factor for hydrophobic organic pollutants. MLPs bind to hydrophobic organic pollutants in the roots, are secreted to xylem vessels as complexes, and are transported to the aerial parts. However, the suitable conditions for binding MLPs to hydrophobic organic pollutants remain elusive. In the present study, we show that MLPs bind to the hydrophobic organic pollutant pyrene with higher affinity under acidic conditions. Our results demonstrated that pH regulates the binding of MLPs to hydrophobic organic pollutants.

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.