The High Light-inducible Polypeptides in Synechocystis PCC6803

Abstract

and an Hli-like polypeptide. By using an epitope tag to identify specifically the different Hli polypeptides, the accumulation of each (excluding HemH) was examined under various environmental conditions. The levels of all of the Hli polypeptides were elevated in high light and during nitrogen limitation, whereas HliA, HliB, and HliC also accumulated to high levels following exposure to sulfur deprivation and low temperature. The temporal pattern of accumulation was significantly different among the different Hli polypeptides. HliC rapidly accumulated in high light, and its level remained high for at least 24 h. HliA and HliB also accumulated rapidly, but their levels began to decline 9 -12 h following the imposition of high light. HliD was transiently expressed in high light and was not detected 24 h after the initiation of high light exposure. These results demonstrate that there is specificity to the accumulation of the Hli polypeptides under a diverse range of environmental conditions. Furthermore, mutants for the individual and combinations of the hli genes were evaluated for their fitness to grow in high light. Although all of the mutants grew as fast as wild-type cells in low light, strains inactivated for hliA or hliC/hliD were unable to compete with wild-type cells during co-cultivation in high light. A mutant lacking all four hli genes gradually lost its photosynthesis capacity and died in high light. Hence, the Hli polypeptides are critical for survival when Synechocystis PCC6803 is absorbing excess excitation energy and may allow the cells to cope more effectively with the production of reactive oxygen species.Light serves as an environmental signal that regulates physiological and developmental processes and provides energy that fuels the reduction of inorganic carbon. However, when photosynthetic organisms absorb excess excitation energy (more than can be used in photosynthesis), the light energy can cause damage to the cell (3, 4). There are several ways in which excess, absorbed, light energy can be harmful to photosynthetic organisms. It can accumulate in light-harvesting antenna complexes and reaction centers and promote the formation of singlet oxygen, superoxides, and hydroxyl radicals, all of which are highly reactive and potentially toxic. Reactive oxygen species could modify proteins, lipids, and nucleic acids, ultimately causing a loss of cell viability (5).The photosynthetic reaction center polypeptide D1, or the 32-kDa polypeptide, is particularly susceptible to damage as a consequence of absorption of excess excitation energy (3, 6 -8); this was first recognized by Kyle et al. (9). The 32-kDa polypeptide, together with the D2 polypeptide, forms the heterodimeric reaction center of photosystem II that binds all of the redox components involved in photosynthetic charge separation. The rapid restoration of photosystem II function following photodamage indicates the existence of a tightly regulated repair system (3). Repair processes include the degradation of damaged D1 polypeptide, de no...

Torn apart and reunited: impact of a heterotroph on the transcriptome of Prochlorococcus

“…Of the first 13 transcripts that changed in abundance 6 h after heterotroph addition, 12 encoded members of the high light inducible (hli) family of stress-responsive proteins (the other is of unknown function; Supplementary Table S2). hlis were originally identified as genes that played a role in protecting cells from light shock (Funk and Vermaas, 1999;He et al, 2001;Bhaya et al, 2002), and are now known to respond to a variety of stresses in Prochlorococcus (Tolonen et al, 2006;Lindell et al, 2007;Thompson et al, 2011; Bagby and Chisholm, 2015). hlis are found in all Prochlorococcus genomes, but NATL2A is notable for having a much larger suite of hlis than many other Prochlorococcus (Coleman and Chisholm, 2007;Kettler et al, 2007;Berta-Thompson, 2015), which may be related to the ability of this clade of low-light adapted Prochlorococcus to withstand transient exposure to high light intensities (Malmstrom et al, 2010).…”

Effects of high light on transcripts of stress-associated genes for the cyanobacteria Synechocystis sp. PCC 6803 and Prochlorococcus MED4 and MIT9313

“…Our results for Prochlorococcus MED4 suggest that considerable protein misfolding and aggregation could take place in surface oceanic waters and that hsp genes could be critical for survival in such an extreme environment. Another example of adaptation of Prochlorococcus MED4 to a HL environment is the high number (22) of hli genes encoded by its genome relative to the genomes of the LL-adapted strains (Bhaya et al, 2002); this gene family is critical for cyanobacterial survival during HL exposure (He et al, 2001),…”

Temporal dynamics of Prochlorococcus ecotypes in the Atlantic and Pacific oceans

“…For example, the two sequenced eNATL isolates each have 41 genes encoding high light-inducible proteins (HLIP), whereas the other LL-adapted ecotypes only have 9-13 HLIP genes (Coleman and Chisholm, 2007). This protein family, also called small cab-like proteins, aids in high-light survival and photoacclimation in Synechocystis (He et al, 2001;Havaux et al, 2003), and may also have a role in light-shock tolerance in eNATL. The mechanism by which they do this remains unclear, but high light-inducible proteins are thought to physically associate with either photosystem and allow it to shed excess energy as heat and thereby reduce photoinactivation (Promnares et al, 2006;Yao et al, 2007).…”