The growth and photosynthetic responses of white LEDs with supplemental blue light in green onion (Allium fistulosum L.) unveiled by Illumina and single-molecule real-time (SMRT) RNA-sequencing

Green onion is an herbaceous plant of the genus Allium in the Liliaceae family, with complex genomes and transcripts. The blue spectrum is necessary for plant photosynthesis. To explore the potential impact of blue light on green onions, we cultivated green onion seedlings under the light intensity of 500 ± 10 μmol·photons·m−2·s−1 white light (W), white-blue combination 3:1 (BW) and monochromatic blue light (B) LED light source. We investigated the diversity of the green onion transcriptome and the differences in transcripts among treatments using a combination of long-read length sequencing and RNA-seq, aiming to assess the effects of supplemental blue light (BW) on the growth and photosynthesis of green onion seedlings. The results showed that BW significantly increased seedling growth and photosynthesis, while B significantly decreased photosynthetic rate and fenestrated tissue layer. Compared to W, 327 and 386 differentially expressed genes (DEGs) were identified under BW and B. DEGs under 3 light conditions were related to photosynthesis, carbon metabolism, photosynthesis - antenna proteins, glyoxylate and dicarboxylate metabolism, sulfur metabolism, porphyrin and chlorophyll metabolism, phototransduction, biosynthesis of amino acids, RNA transport, carbon fixation in photosynthetic organisms, etc. pathways were closely related. Our results showed that white LEDs with supplemental blue light significantly improves the growth of green onion seedlings by regulating photosynthesis-related genes compared with white light. In conclusion, white LEDs with supplemental blue light could promote the growth of green onion in a controlled environment.