An Overview of Plant Photosynthesis Modulation by Pathogen Attacks

In 1893, Charles Barnes (1858-1910) proposed to designate the biological process for “synthesis of complex carbon compounds out of carbonic acid, in the presence of chlorophyll, under the influence of light” as “photosyntax” or “photosynthesis”. His preference went for the word “photosyntax”, but “photosynthesis” came into common usage as the term of choice (Gest, 2002). Although this definition is still widely used today, the Oxford English Dictionary (OED, 1989) has defined the biological photosynthesis as “the process by which carbon dioxide is converted into organic matter in the presence of the chlorophyll of plants under the influence of light, which in all plants except some bacteria involves the production of oxygen from water”. By considering the photosynthetic bacteria that do not produce oxygen and do not necessarily require carbonic acid as carbon source, Gest (Gest, 1993) has refined these definitions as followed: “photosynthesis is a series of processes in which electromagnetic energy is converted to chemical energy used for biosynthesis of organic cell materials; a photosynthetic organism is one in which a major fraction of the energy required for cellular syntheses is supplied by light”. Photosynthesis is therefore a unique source for carbon sequestration and allows the aerobic organisms to survive based upon not only on its released oxygen but also its synthesized organic compounds. As such, plants are an ideal host for pathogenic microorganisms such as fungi, bacteria and viruses and also the only food source for herbivores. Theoretically, the photosynthetic capacity of plants is unlimited when the optimal growing conditions are met. Unfortunately, terrestrial plants are constantly challenged by abiotic (UV, water, salinity, temperature) (Baker et al., 1988, Baldry et al., 1966, Barhoumi et al., 2007, Barrow and Cockburn, 1982, Bassham, 1977, Batista-Santos et al., 2011, Bauerle et al., 2007, Berry, 1975, Bischof et al., 2000, Ripley et al., 2008, Ripley et al., 2007, Roberntz and Stockfors, 1998) and biotic (pathogens, pests, animal and human) stresses that reduce their productivity and even threaten their survival (Bilgin et al., 2010, Bonfig et al., 2006, Erickson and Hawkins, 1980, Garavaglia et al., 2010, Kocal et al., 2008, Tang et al., 2009). While the regulation of plant defence responses has been extensively investigated, the effects of pathogen infection on primary metabolism, including photosynthesis, are however less known. Currently, interest in this research area is growing and some aspects of photosynthesis, assimilate