Phlobaphenes modify pericarp thickness in maize and accumulation of the fumonisin mycotoxins

Abstract

Phlobaphenes are insoluble phenolic compounds which are accumulated in a limited number of tissues such as seed pericarp and cob glumes, conferring on them a typical red-brown pigmentation. These secondary metabolites, derived from 3-deoxy flavonoids, are thought to have an important role in plants' resistance against various pathogens, e.g. by reducing fungal infection, and also to have beneficial effects on human and animal health due to their high antioxidant power. The aim of this work was to determine the role of phlobaphenes in reducing mycotoxin contamination on maize kernels. We analysed the effect of the P1 (pericarp color 1) gene on phlobaphenes accumulation, pericarp thickness and fumonisins accumulation. Analysing fumonisins accumulation in different genetic backgrounds through three seasons, we found a clear decrease of these toxins through the three years (Wilcoxon test, Z = 2.2, p = 0.0277) in coloured lines compared with the isogenic non-coloured ones. The coloured lines, carrying P1 allele showed an increase of phlobaphenes (about 10-14 fold) with respect to colourless lines. Furthermore there was a correlation between phlobaphenes accumulation and pericarp thickness (R = 0.9318; p = 0.0067). Taken together, these results suggest that the P1 gene plays a central role in regulating phlobaphenes accumulation in maize kernels, and indirectly, also tackles mycotoxins accumulation. The development and cultivation of corn varieties rich in phlobaphenes could be a powerful tool to reduce the loss of both quality and yield due to mycotoxin contamination, increasing the safety and the quality of the maize product.

Figure 1

Mature seeds of the maize lines used in this work: Syn1c (A), Syn1r (B) Syn2c (C), Syn2r (D), Nsw (E), Nsr (F). Scheme of the crosses performed to obtain Syn populations (G).

Figure 2

Histological analysis of mature seeds pericarp thickness: Syn1c (A), Syn1r (B), Syn2c (C), Syn2r (D), Nsw (E) and Nsr (F).

Figure 3

Correlation analysis between phlobaphenes amount and pericarp thickness of the seed in Syn1c, Syn1r, Syn2 c, Syn2r, Nsw and Nsr.

Figure 4

Scheme explaining how the Ac excision from P1 gene produced somatic sectors due to the reactivation of phlobaphenes pathway (A). Seed sectors caused by Ac excision from the locus p1 (PVV unstable allele). (C) Histological analysis of mature PVV seeds and pericarp thickness of colorless and red sectors.