A Major Latex-Like Protein Is a Key Factor in Crop Contamination by Persistent Organic Pollutants    

Abstract

This is the first report, to our knowledge, to reveal important factors by which members of the Cucurbitaceae family, such as cucumber (Cucumis sativus), watermelon (Citrullus lanatus), melon (Cucumis melo), pumpkin (Cucurbita pepo), squash (C. pepo), and zucchini (C. pepo), are selectively polluted with highly toxic hydrophobic contaminants, including organochlorine insecticides and dioxins. Xylem sap of C. pepo ssp. pepo, which is a high accumulator of hydrophobic compounds, solubilized the hydrophobic compound pyrene into the aqueous phase via some protein(s). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of xylem sap of two C. pepo subspecies revealed that the amount of 17-kD proteins in C. pepo ssp. pepo was larger than that in C. pepo ssp. ovifera, a low accumulator, suggesting that these proteins may be related to the translocation of hydrophobic compounds. The protein bands at 17 kD contained major latex-like proteins (MLPs), and the corresponding genes MLP-PG1, MLP-GR1, and MLP-GR3 were cloned from the C. pepo cultivars Patty Green and Gold Rush. Expression of the MLP-GR3 gene in C. pepo cultivars was positively correlated with the band intensity of 17-kD proteins and bioconcentration factors toward dioxins and dioxin-like compounds. Recombinant MLP-GR3 bound polychlorinated biphenyls immobilized on magnetic beads, whereas recombinant MLP-PG1 and MLP-GR1 did not. These results indicate that the high expression of MLP-GR3 in C. pepo ssp. pepo plants and the existence of MLP-GR3 in their xylem sap are related to the efficient translocation of hydrophobic contaminants. These findings should be useful for decreasing the contamination of fruit of the Cucurbitaceae family as well as the phytoremediation of hydrophobic contaminants.

Bioaccumulation and translocation of polyhalogenated compounds in rice (Oryza sativa L.) planted in paddy soil collected from an electronic waste recycling site, South China

“…Additionally, liquid culture medium was used and the plants are two zucchini cultivars not rice in study of Inui et al, which can also affect the observed correlation between TF and log Kow. Inui et al (2013) reported that the presence of major latex-like proteins and the high expression of the MLP-GR3 gene in the xylem sap of plants belonging to the Cucurbitaceae family are related to the efficient translocation of hydrophobic contaminants. Our results indicate that the affinity of chemicals to xylem sap proteins is hydrophobicity-dependent.…”

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

“…Of the cucurbits, C. pepo, including pumpkins and zucchini, are high accumulators, and subspecies-level variation in the accumulation of DDE (White et al, 2003b), and dioxins and dioxin-like compounds (Inui et al, 2008) has been observed. This subspecies variation has been explained in terms of the expression levels of MLP genes in roots, as well as by the amount of MLPs in xylem sap (Inui et al, 2013). MLP-GR3 is particularly important for PCB accumulation in the aerial parts of C. pepo, as indicated by the fact that its expression level in high accumulators is higher than that in low accumulators and that it binds PCBs.…”

“…These results suggest that mechanisms for desorbing hydrophobic compounds from the soil and translocating them to aerial plants parts are critical factors that distinguish Cucurbitaceae from other plants. Recently, we reported that some major latex-like proteins (MLPs) in cucurbit roots bind polychlorinated biphenyls (PCBs), which are then translocated to aerial parts through the xylem sap (Inui et al, 2013).…”

Biodegradation of γ-hexachlorocyclohexane by transgenic hairy root cultures of Cucurbita moschata that accumulate recombinant bacterial LinA

“…In recent years, species-specific Cucurbita proteins related to POPs uptake and translocation were isolated in xylem saps and their characters investigated (Murano et al 2010;Inui et al 2013). However, even if Cucurbita species were used for phytoremediation of HCH in soils, it would be insufficient for mitigating contamination by POPs, because plants lack enzymes that degrade HCH.…”