Probing molecular events associated with early development of thylakoid membranes by comparative proteomics and low temperature fluorescence

Abstract

A comparison of protein profiles between prolamellar bodies from dark-grown etioplasts and thylakoid membranes from de-etioplasts illuminated respectively for 1, 5 and 9h revealed 155 differentially expressed CBB-stained spots. Clear results showed that the nonphototransformable Pchlide627-632 was the dominant pigment form in the PLBs of rice etioplasts during plant development in dark and transformed slowly to chlorophyllide in rice etioplasts when exposed to light. The light-induced accumulation of ACC oxidase, which catalyzes the final step of ethylene synthesis using ACC as substrate, would facilitate chlorophyll synthesis by inducing PORa/b expression via ethylene signaling. It could be also suggested that cyclic electron transport might play an important role in generation of ATP for carbon fixation and photoprotection of photosystems from excessive light in prothylakoid. Furthermore, the overproduction of ClpC1, which targets proteins to the ClpPR core complex for degradation, was observed only in Stage 1, during which period PLBs disrupted and converted into prothylakoids, suggesting that ClpC1 was of particular importance for disassembly of PLBs of etioplasts when exposed to light. This study revealed the possible biochemical and physiological processes lead to the formation of functional thylakoid membranes.

Biological significance: In this study, we monitored the light-induced transformation of prolamellar bodies into thylakoid membranes, which is correlated to the biogenesis of photosynthetic apparatus involving a complex cascade of biochemical and structural events. Three stages of thylakoid development classified according to the thylakoid development status (Adam et al., 2011) were studied for biogenesis of photosynthetic apparatus: Stage 1, prothylakoids emerge from the disrupted PLBs; Stage 2, prothylakoids converted into primary thylakoids which were dispersed in the stroma; Stage 3, the continuous grana and stroma thylakoids are formed. The development stage-dependent changes in the proteomic profile of the thylakoids were analyzed by two-dimensional electrophoresis (2-DE). This information was complemented with the steady-state 77K chlorophyll fluorescence of thylakoids at the corresponding development stage. Together, these analyses allowed us to further understand the molecular processes connected to the formation of functional thylakoid membranes.

Keywords: Chlorophyll; Development; Proteomics; Thylakoid.