Comparative transcriptome and metabolomic analysis reveal key genes and mechanisms responsible for the dark-green leaf color of a strawberry mutant

Photosynthesis is a source of energy for various types of plant life activities and is essential for plant growth and development. Consequently, the study of photosynthetic mechanisms has been a hot spot. Leaf color mutants has always been ideal materials for exploring the mechanisms of chlorophyll metabolism and photosynthesis. In this study, we identified a leaf color mutant of 'Benihoppe' strawberry in the field, which exhibited a darker green leaf color compared with the wild type. The content of total chlorophyll and carotenoid in the mutant leaves was elevated by 7.44-20.23% and 8.9-21.92%, respectively, compared with that of the wild type. Additionally, net photosynthetic rate in the mutant increased by 20.13%. Further transcriptome analysis showed that significant upregulation of genes such as GLK1, PPR, and MORF9 in the mutant leaves, which promoted chloroplast development. The expression levels of UROD, PPOC, PORA, CHLG, and CPOX were significantly upregulated during chlorophyll synthesis, while the expression levels of HCAR and CYP89A9 were significantly down- regulated during chlorophyll degradation, thus leading to the accumulation of chlorophyll in mutant leaves. The upregulation of gene expression levels such as PetM, AtpD, PGK, and RPI4 during photosynthesis promoted multiple stages of light and dark reaction, thereby enhancing the photosynthetic capacity of the mutant. And the changes in metabolites such as monogalactosyl monoacylglycerol (MGMG), glucuronosyldiacylglycerol (GlcADG), raffinose, etc. also indicate that the mutant has metabolic differences in chloroplast composition and photosynthesis compared to 'Benihoppe'. The above results not only deepen our understanding of the mechanism behind the dark-green leaf color in strawberry mutants but also provide potential genetic resources for cultivating strawberry varieties with enhanced photosynthetic capacity.