Peptide mass fingerprinting of rice (Oryza sativa L.) leaves during UV-B induced stress at seedling stage: A proteom analysis

The depletion of stratospheric ozone layer has led to the increase in solar ultraviolet (UV-B: 280-320 nm) radiation reaching the Earth’s surface and resulted in reduction of the growth and yield of crop plants. To defend against such adverse effect, plants may have developed some kind of resistance mechanism through differential expression of genes involved in UV stress. To determine the differentially expressed proteome in 3 local rice (Oryza sativa L.) cultivars, namely, Sadamala, Lalmala and Paijam, 15-d-old seedlings were exposed to ultraviolet-B radiation (UV-B: 280-320 nm) for 4, 8 and 12 h duration. The leaf proteins were separated through SDS-PAGE to detect the differentially expressed protein for proteomic analysis. Further, mass spectrometry (MS) and bioinformatics were used to study the proteomic responses in the leaves of the rice seedlings. An extra unique band was detected at around 60 kDa size range in the cultivar Sadamala only after 8 h treatment when compared to control sample. However, differentially expressed protein band was not detected in the other two cultivars of Lalmala and Paijam probably because they may be sensitive to UVB irradiation as compared to cultivar Sadamala. Proteins in this extra band were identified by peptide mass fingerprinting (PMF) through nanoLC-ESI-MS/MS technique. Twenty-seven different proteins were thus identified from this extra band in PMF while performing a database search using MASCOT in NCBInr. These proteins include stress inducible and differentially expressed proteins, such as, ST-1 (stress inducible protein-1), putative chaperonin 60 β-precursor, Rubisco subunit binding-protein β-subunit, heat shock cognate 70 kDa (Hsp70) protein, putative malate dehydrogenase, putative endosperm specific protein SC3, α-L-arabinofuranosidase and others. These results suggest that there may exist some kind of UV protective mechanism in rice plant to tolerate UV-B exposure.