Modeling the photosynthetic system I as complex interacting network

Abstract

In this paper we model the excitation energy transfer (EET) of the photosynthetic system I (PSI) of the common pea plant Pisum Sativum as complex interacting network. The magnitude of the link energy transfer between nodes-chromophores is computed by Forster Resonant Energy Transfer (FRET) using the pairwise physical distances between chromophores from the PDB (Protein Data Bank). We measure the global PSI network EET efficiency adopting well-known network theory indicators: the network efficiency (Eff) and the largest connected component (LCC). We find that when progressively removing the weak links of lower EET, the network efficiency (Eff) decreases while the EET paths integrity (LCC) is still preserved. This finding would show that the PSI is a resilient system owning a large window of functioning feasibility and it is completely impaired only when removing most of the network links. Furthermore, we perform nodes removal simulations to understand how the nodes-chromophores malfunctioning may affect the PSI functioning. We discover that the removal of the core chlorophylls triggers the fastest decrease in the network efficiency (Eff), unveiling them as the key component boosting the high EET efficiency. Our outcomes open new perspectives of research, such comparing the PSI energy transfer efficiency of different natural and agricultural plant species and investigating the light-harvesting mechanisms of artificial photosynthesis both in plant agriculture and in the field of solar energy applications. Keywords: Complex network, photosystem I, photosynthetic network, biological network, network robustness, network attack.been directed to unveil the underneath structural and topological patterns shaping the high EET efficiency of the PSI system [2,3].The purpose of this research is the analysis of the structural organization of a plant PSΙ as a complex networked system for EET by means of network science viewpoint. Network science has proven to be a powerful tool for the study of complex systems from many different realms [18][19][20][21][22][23][24][25][26] . Basically, a network is a model composed by nodes (or vertices) and links (edges), where nodes indicate the components of the system and the links define the interactions among them [27,28] . Here we model the PSΙ light-harvesting system of the plant Pisum sativum as a complex network of nodeschromophores describing the energy transfer links among them. First, we find that the PSI is a highly connected network with very short EET pathways from the nodes harvesting the light to the RC.Second, we discover that the capacity to perform EET in the whole network is severely impaired only by removing the major amount of EET links. This unveils the high resilience of the PSI system, which holds the capacity to perform the energy transfer in the whole network even reaching severe conditions for its feasibility. Last, we simulate different scenarios of chromophores malfunctioning by removing nodes from the network [18,29]. We find that the removal towards the core Chl...