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...

Traits such as grain shape, panicle length and seed shattering, play important roles in grain yield and harvest. In this study, the cloning and functional analysis of PANICLE TRAITS 2 (PT2), a novel gene from the Indica rice Chuandali (CDL), is reported. PT2 is synonymous with Growth‐Regulating Factor 4 (OsGRF4), which encodes a growth‐regulating factor that positively regulates grain shape and panicle length and negatively regulates seed shattering. Higher expression of OsGRF4 is correlated with larger grain, longer panicle and lower seed shattering. A unique OsGRF4 mutation, which occurs at the OsmiRNA396 target site of OsGRF4, seems to be associated with high levels of OsGRF4 expression, and results in phenotypic difference. Further research showed that OsGRF4 regulated two cytokinin dehydrogenase precursor genes (CKX5 and CKX1) resulting in increased cytokinin levels, which might affect the panicle traits. High storage capacity and moderate seed shattering of OsGRF4 may be useful in high‐yield breeding and mechanized harvesting of rice. Our findings provide additional insight into the molecular basis of panicle growth.

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