Chloroplasts are the center of plant life activities including photosynthesis, growth and development, and abiotic stress response. Chloroplast development and biogenesis in rice have been studied in detail, but how does abiotic stress affect chloroplasts is less studied. We obtained an albino mutant, alm1, whose chlorophyll content was greatly decreased. Transmission electron microscopy showed that chloroplast development in alm1 was blocked, especially in thylakoid-like structures, which could not form normally. The ALM1 gene encodes a chloroplast-localized superoxide dismutase. Full-length ALM1 successfully restored the non-albino phenotype, and in knockout lines, the albino phenotype reappeared. The ALM1 gene is expressed mainly in young leaves. alm1 plants died as a consequence of excessive reactive oxygen accumulation after the third-leaf stage. A series of biochemical assays verified that ALM1 interacted with the OsTrxz protein, which is one of the components of plastid-encoded RNA polymerase (PEP) complexes. A western blot experiment indicated that ALM1 played an important role in stabilizing OsTrxz in rice. An overexpression test of ALM1 revealed that ALM1 can increase drought resistance by removing excess reactive oxygen in rice seedlings. This study suggests that ALM1 not only participates in rice chloroplast biogenesis, but also increases rice stress resistance by scavenging excess reactive oxygen.

Abiotic stresses such as drought, salinity, and low temperature cause–losses in rice production worldwide. The emergence of transgenic technology has enabled improvements in the drought resistance of rice plants and helped avert crop damage due to drought stress. Selectable marker genes conferring resistance to antibiotics or herbicides have been widely used to identify genetically modified plants. However, the use of such markers has limited the public acceptance of genetically modified organisms. Marker-free materials (i.e., those containing a single foreign gene) may be more easily accepted by the public and more likely to find common use. In the present study, we created marker-free drought-tolerant transgenic rice plants using particle bombardment. Overall, 842 T₀ plants overexpressing the rice ascorbate peroxidase-coding gene OsAPX2 were generated. Eight independent marker-free lines were identified from T₁ seedlings using the polymerase chain reaction. The molecular characteristics of these lines were examined, including the expression level, copy number, and flanking sequences of OsAPX2, in the T₂ progeny. A simulated drought test using polyethylene glycol and a drought-tolerance test of seedlings confirmed that the marker-free lines carrying OsAPX2 showed significantly improved drought tolerance in seedlings. In the field, the yield of the wild-type plant decreased by 60% under drought conditions compared with normal conditions. However, the transgenic line showed a yield loss of approximately 26%. The results demonstrated that marker-free transgenic lines significantly improved grain yield under drought-stressed conditions.