Ultraviolet Radiation From a Plant Perspective: The Plant-Microorganism Context

Abstract

Ultraviolet (UV) radiation directly affects plants and microorganisms, but also alters the species-specific interactions between them. The distinct bands of UV radiation, UV-A, UV-B, and UV-C have different effects on plants and their associated microorganisms. While UV-A and UV-B mainly affect morphogenesis and phototropism, UV-B and UV-C strongly trigger secondary metabolite production. Short wave (<350 nm) UV radiation negatively affects plant pathogens in direct and indirect ways. Direct effects can be ascribed to DNA damage, protein polymerization, enzyme inactivation and increased cell membrane permeability. UV-C is the most energetic radiation and is thus more effective at lower doses to kill microorganisms, but by consequence also often causes plant damage. Indirect effects can be ascribed to UV-B specific pathways such as the UVR8-dependent upregulated defense responses in plants, UV-B and UV-C upregulated ROS accumulation, and secondary metabolite production such as phenolic compounds. In this review, we summarize the physiological and molecular effects of UV radiation on plants, microorganisms and their interactions. Considerations for the use of UV radiation to control microorganisms, pathogenic as well as non-pathogenic, are listed. Effects can be indirect by increasing specialized metabolites with plant pre-treatment, or by directly affecting microorganisms.

Keywords: UV-C; plant-microorganism interaction; plants; ultraviolet; ultraviolet-A; ultraviolet-B.

FIGURE 1

Absorption spectra of UV-B absorbing photoreceptors in Arabidopsis. (A) UVR8 absorption is recorded in the UV-C and UV-B region of the spectrum. (B) CRY1 and CRY2 absorb both strongly in blue and UV-A radiation with indication that CRY1 strongly absorbs in the UV-B band. (C) PHOT1 and PHOT2 both absorb mainly in the blue and UV-A wavelengths of the spectrum with indications that PHOT1 also absorbs UV-B. (D) PHY proteins have an absorption peak in red and far red wavelengths but also absorb UV-A and UV-B (Ahmad et al., 2002; Kasahara et al., 2002; Sang et al., 2005; Christie et al., 2012).

FIGURE 2

Ultraviolet induced flavonoid accumulation is UVR8 and CRY dependent. UV-B activates UVR8 (Kaiserli and Jenkins, 2007; Yin et al., 2016) which leads to HY5 accumulation and thus diverse flavonoid biosynthesis via CHS, CHI, FH3, and FLS1 (Hideg et al., 2013). CRYs are activated via UV-A and regulate HY5, causing flavonoid accumulation in a similar way as described for UVR8 but also DFR regulation was reported for UV-A conditions (Morales et al., 2013). R-groups are indicated for substances mentioned throughout the text. Red dashed arrows indicate induction of specific enzymes by HY5.