Thylakoid proteome modulation in pea plants grown at different irradiances: quantitative proteomic profiling in a non‐model organism aided by transcriptomic data integration

Abstract

Plant thylakoid membranes contain hundreds of proteins that closely interact to cope with ever-changing environmental conditions. We investigated how Pisum sativum L. (pea) grown at different irradiances optimizes light-use efficiency through the differential accumulation of thylakoid proteins. Thylakoid membranes from plants grown under low (LL), moderate (ML) and high (HL) light intensity were characterized by combining chlorophyll fluorescence measurements with quantitative label-free proteomic analysis. Protein sequences retrieved from available transcriptomic data considerably improved thylakoid proteome profiling, increasing the quantifiable proteins from 63 to 194. The experimental approach used also demonstrates that this integrative omics strategy is powerful for unravelling protein isoforms and functions that are still unknown in non-model organisms. We found that the different growth irradiances affect the electron transport kinetics but not the relative abundance of photosystems (PS) I and II. Two acclimation strategies were evident. The behaviour of plants acclimated to LL was compared at higher irradiances: (i) in ML, plants turn on photoprotective responses mostly modulating the PSII light-harvesting capacity, either accumulating Lhcb4.3 or favouring the xanthophyll cycle; (ii) in HL, plants reduce the pool of light-harvesting complex II and enhance the PSII repair cycle. When growing at ML and HL, plants accumulate ATP synthase, boosting both cyclic and linear electron transport by finely tuning the ΔpH across the membrane and optimizing protein trafficking by adjusting the thylakoid architecture. Our results provide a quantitative snapshot of how plants coordinate light harvesting, electron transport and protein synthesis by adjusting the thylakoid membrane proteome in a light-dependent manner.

Structural and functional differentiation of the light‐harvesting protein Lhcb4 during land plant diversification

“…Noteworthy, the pattern of expression of the LHCB4.3 gene was found more similar to that of PSBS , with respect to that of other LHC genes (Klimmek et al ), suggesting a cooperative function of the corresponding proteins under conditions where elevated capacity for non‐radiative energy dissipation is of physiological relevance. Because the amount of both, Lhcb4.3 and PsbS, significantly increases in thylakoids of plants exposed to high irradiances (Albanese et al ), we hypothesize that PsbS might interact with Lhcb4.3 to regulate the PSII‐LHCIIsc organization in high light, ultimately controlling their macro‐organization in the grana membranes (Kereïche et al ).…”

“…In some flowering plants, as the model organism A. thaliana , this subunit differentiated in up to three isoforms, Lhcb4.1, Lhcb4.2 and Lhcb4.3. Contrarily to LHCB4.1 and LHCB4.2 , the LHCB4.3 gene is strongly upregulated in moderate and high light, as attested at level of transcription (Alboresi et al ), translation (Floris et al ) and protein expression (Albanese et al , Miller et al , Albanese et al ). The increased accumulation of the Lhcb4.3 subunit observed in PSII‐LHCIIsc of plants acclimated to increasing intensity of light (Albanese et al ), induced us to investigate whether this isoform has a preferential localization in a specific PSII‐LHCIIsc conformation that might explain a light‐regulated function for this protein.…”

“…The degree of rotation of the M-trimer is shown as reported in Kouřil et al (2016) and Drop et al (2014). et al 2016a, Miller et al 2017, Albanese et al 2018. The increased accumulation of the Lhcb4.3 subunit observed in PSII-LHCIIsc of plants acclimated to increasing intensity of light (Albanese et al 2016a), induced us to investigate whether this isoform has a preferential localization in a specific PSII-LHCIIsc conformation that might explain a light-regulated function for this protein.…”

“…The L and M conditions were provided with 3 and 15 fluorescent lamps FL40SS W/37 (Sanyo), of 40 W each, respectively; the H light condition was supplied by four LEDs LXR7‐SW50 (Agonlight), of 35 W each, mounted inside the growth chamber. Both types of light sources have similar spectral power distribution curves (Albanese et al ).…”

“…Lhcb6 is one of the latest outcomes of evolution, being present only in land plants (Alboresi et al 2008), where it is important to maintain the macro-organization of the grana membranes (Kovács et al 2006), but eventually evolutionarily lost in some gymnosperms in concomitance with Lhcb3 (Kouřil et al 2016). Its expression is affected by light intensity, being Lhcb6 less abundant in plants grown under high irradiances (Albanese et al 2016a, Albanese et al 2018. Lhcb4 is ubiquitous in all classes of green plants (Koziol et al 2007), and its presence is mandatory for maintaining the thylakoid macrostructure and the proper assembly of PSII-LHCIIsc (de Bianchi et al 2011).…”