Red and blue light treatments of ripening bilberry fruits reveal differences in signalling through abscisic acid-regulated anthocyanin biosynthesis.

Amos Samkumar,Andrew P Dare,Nina Sipari,Laura Jaakola,Katja Karppinen,Inger Martinussen,Richard V Espley,Dan Jones

doi:10.1111/pce.14158

Abstract

The biosynthesis of anthocyanins has been shown to be influenced by light quality. However, the molecular mechanisms underlying the light-mediated regulation of fruit anthocyanin biosynthesis are not well understood. In this study, we analysed the effects of supplemental red and blue light on the anthocyanin biosynthesis in non-climacteric bilberry (Vaccinium myrtillus L.). After 6 days of continuous irradiation during ripening, both red and blue light elevated concentration of anthocyanins, up to 12- and 4-folds, respectively, compared to the control. Transcriptomic analysis of ripening berries showed that both light treatments up-regulated all the major anthocyanin structural genes, the key regulatory MYB transcription factors and abscisic acid (ABA) biosynthetic genes. However, higher induction of specific genes of anthocyanin and delphinidin biosynthesis alongside ABA signal perception and metabolism were found in red light. The difference in red and blue light signalling was found in 9-cis-epoxycarotenoid dioxygenase (NCED), ABA receptor pyrabactin resistance-like (PYL) and catabolic ABA-8'hydroxylase gene expression. Red light also up-regulated expression of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) domain transporters, which may indicate involvement of these proteins in vesicular trafficking of anthocyanins during fruit ripening. Our results suggest differential signal transduction and transport mechanisms between red and blue light in ABA-regulated anthocyanin and delphinidin biosynthesis during bilberry fruit ripening.

Highlights

Light is among the most important environmental factors modifying plant growth and development
The abscisic acid (ABA) signal transduction is known to be mediated by pyrabactin resistance/like (PYR/pyrabactin resistance-like (PYL)) receptors and ABA-responsive elementbinding factors (ABFs) through SQUAMOSA-MADS box (TDR-type) transcription factors (TFs) leading to regulation of the MBW complex proteins (Chung et al, 2019)
Our study showed that during the red light light-emitting diodes (LEDs) treatment, phytochrome B (PHYB) expression was up-regulated together with constitutive photomorphogenesis protein 1 (COP1) and hypocotyl 5 (HY5), the key genes involved in photomorphogenesis, alongside photoperiodism-related early flowering (ELF3) and CK2α genes (Figure 6)

Summary

| INTRODUCTION

Light is among the most important environmental factors modifying plant growth and development. R2R3 MYB TFs are known as the key regulators of anthocyanin biosynthesis and are responsive to shifts in light spectral quality (Zoratti, Karppinen, et al, 2014). The ABA signal transduction is known to be mediated by pyrabactin resistance/like (PYR/PYL) receptors and ABA-responsive elementbinding factors (ABFs) through SQUAMOSA-MADS box (TDR-type) TFs leading to regulation of the MBW complex proteins (Chung et al, 2019). Another model has been proposed, illustrating that ABA interacts directly with PYR by inhibiting type 2C protein phosphatases subsequently binding with ABFs and transduces the ABA signalling pathway (Park et al, 2009). The red and blue light-emitting diodes (LEDs) used in our study give an opportunity to provide high intensity spectral wavelengths to plants as source of light for studying the effect of light quality to biosynthesis of phytochemicals

| MATERIALS AND METHODS

| RESULTS

Findings

| DISCUSSION

| CONCLUSION