Analysis of mechanisms underlying accelerated plant growth induced by NtGLK85 overexpression in tobacco

The Golden2-like (GLK) genes play a crucial role in chloroplast development in angiosperms. Our previous study revealed a strong correlation between the expression level of the NtGLK85 gene and the development and maturation of tobacco leaves. Therefore, exploring the regulatory mechanisms controlled by NtGLK85 during plant growth and development is of significant importance. We generated an overexpression line of NtGLK85 in the tobacco cultivar K326, designated as D710. Both the transgenic lines (T2) and its control K326 were planted in the field. Phenotypic investigation found that D710 exhibited a faster growth rate and shorter growth cycle compared to the wild-type K326. Samples were collected at three stages: 30 days (A), 45 days (B), and 65 days (C) after transplantation. Physiological and biochemical analysis showed that, at stages A and B, D710 had higher chlorophyll content, total sugar, starch levels, and plant height compared to K326. However, at stage C, the chlorophyll content, total sugar, and starch levels in D710 were lower than in K326, although the plant height was similar. Transcriptome sequencing (RNA-Seq) was performed on samples from all three stages, generating a total of 374,627,262 clean reads. Comparative analysis of the data between K326 and D710 at the three stages identified 1,663 differentially expressed genes (DEGs) at stage A, 1,320 DEGs at stage B, and 1,244 DEGs at stage C. GO and KEGG analysis revealed that these DEGs were predominated associated with plant growth and development. Significant differences were observed in the expression of genes involved in five key pathways related to plant growth and development, including photosynthesis (map00195), fatty acid biosynthesis (map00061), cutin, suberin and wax biosynthesis (map00073), carbon fixation in photosynthetic organisms (map00710), and fatty acid elongation (map00062). These differences were attributed to the NtGLK85 overexpression. The overexpression of NtGLK85 increases chlorophyll content in the tobacco leaves, thereby enhancing carbohydrate synthesis and accumulation during the early growth stages. As a result, the D710 line exhibited accelerated growth and a shortened life cycle compared to the wild-type K326.