Comparative Proteomics Analysis of Primulina serrulata Leaves Reveals New Insight into the Formation of White Veins

Primulina serrulata is a valuable ornamental herb with rosette leaves and vibrant flowers. Some leaves of this species exhibit a bright and distinct white color along the upper veins, enhancing their ornamental value, while others are less white or entirely green. This variation is observed in adult leaves from natural habitats and among young leaves from seedlings grown in the laboratory. TMT-labeled proteomics technology was used to study the protein-level biogenesis of white-veined (WV) P. serrulata leaves. Our objective was to offer novel insight into the breeding of WV plants. Chlorophyll (Chl) content was significantly lower in the WV group than in the control group. Out of 6261 proteins identified, a mere 69 met the criteria for differentially expressed proteins (DEPs) after stringent screening for subsequent analyses. Among these DEPs, there were 44 proteins that exhibited downregulation and 25 that were upregulated in the WV plants. Some DEPs associated with chloroplasts and Chl biosynthesis were downregulated, leading to the absence of green coloration. Concurrently, Gene Ontology enrichment analysis further emphasized an insufficiency of magnesium, the key element in Chl biosynthesis. Many DEPs associated with abiotic or biotic stressors were downregulated, suggesting an overall weakening of stress resistance with certain compensatory mechanisms. Similarly, many DEPs related to modifying biomacromolecules were downregulated, possibly affected by the decrease in proteins involved in photosynthesis and stress resistance. Some DEPs containing iron were upregulated, indicating that iron is mainly used to synthesize heme and ferritin rather than Chl. Additionally, several DEPs related to sulfur or sulfate were upregulated, suggesting strengthened respiration. Expansin-A4 and pectinesterase were upregulated, coinciding with the emergence of a rough and bright surface in the white area of leaves, indicative of the elongation and gelation processes in the cell walls. These findings provide new insight for future studies to explore the mechanism of color formation in WV leaves.