Interactive effects of light quality and nitrate supply on growth and metabolic processes in two lettuce cultivars (Lactuca sativa L.)

Abstract

Light quality and nutrient parameters alter plant growth and metabolic pathways in leafy greens, therefore being primarily optimized in indoor precision agriculture. While their individual effects were studied extensively with large-scale phenomics and transcriptomics, the combinatorial effects remain poorly understood. Here, we explored the hidden interactions among light- and nitrate-responsive transcriptomes and their associations with six growth and biochemical traits, using the full factorial experimental design with three lights (red (R), blue (B) and a 1:1 mixture of red and blue (RB)), two nitrate concentrations and two cultivars (Green oak-leaf and Red oak-leaf). Multifactor analysis of 36 RNA-sequencing data revealed their largely independent but additive effects that are associated with MYB, bHLH and GATA family transcription factors. Red light and sufficient nitrate supply additively increased the primary metabolite pathway and bHLH and GATA genes, leading to a high growth rate. Blue and RB lights, together with nitrate deficiency, induced flavonoid pathway and MYB genes. Variety-specific deviations were detected in late anthocyanin biosynthetic genes and specific MYB transcription factors that would explain anthocyanin accumulations in the Red oak-leaf cultivar. Taken together, our large-scale transcriptomic and physiologic results suggest that the two environmental parameters (i.e., light quality and nitrate level) (1) utilize independent transcriptional regulatory mechanisms to achieve similar phenotypic and metabolic changes, and (2) induce the variety-specific anthocyanin accumulations via a small number of genes that show different gene expression profiles between the two cultivars.