Transcriptomic analysis reveals the mechanism of leaf yellowing in Nicotiana tabacum L.

Abstract

Background Leaf color affects the yield and quality of flue-cured tobacco. At present, the cost of labor for the harvesting of tobacco in batches is high. It is difficult to realize mechanized operations. The yellow leaf mutant of tobacco discovered by the research group can promote the maturity of tobacco leaves and improve the centralized maturity of tobacco leaves. However, its yellowing mechanism remains poorly understood.

Objective This study providing a new insights into both physiological and molecular aspects of the leaf yellowing mechanism.

Methods We compared the yellow leaf mutant (Y), the normal green plant K326 (K) and backcross material yellow leaf K326 (KY) in physiology, cytology, and transcription spectrum.

Results In the present study, we found that the total chlorophyll content of the two yellow leaf plants before maturity was significantly lower than that of normal plant, and the thylakoid structure was incomplete. A total of 3551 differentially expressed genes were identified in the transcriptome. The synthesis of Mg-Proto IX, abnormal thylakoid structure and the chlorophyll content in leaves were significantly reduced, which was due to the significant reduction in the expression of chlorophyll synthesis genes ChlH and ChlD and chloroplast development gene PPR. We speculate that the expression changes of the zeatin synthesis gene CISZOG and the degradation gene CKX in the yellow leaves, and inhibit chlorophyll synthesis by reducing the zeatin content and the expression of ChlH. FPGS gene, folB gene and metabolic pathway GGH gene expression are altered in yellow leaves to inhibit chlorophyll synthesis by reducing folate content. The above is the main reason for the yellowing of tobacco leaves. 

Conclusion By comparing yellow leaf and green leaf tobacco varieties, this study not only confirms the important role of chlorophyll and chloroplasts in yellow leaf leaf coloration, but also provides new insights into the transcriptome resolution mechanism of leaf color mutation.