Chloroplasts are plant organelles that carry out photosynthesis, produce various metabolites, and sense changes in the external environment. Given their endosymbiotic origin, chloroplasts have retained independent genomes and gene-expression machinery. Most genes from the prokaryotic ancestors of chloroplasts were transferred into the nucleus over the course of evolution. However, the importance of chloroplast gene expression in environmental stress responses have recently become more apparent. Here, we discuss the emerging roles of the distinct chloroplast gene expression processes in plant responses to environmental stresses. For example, the transcription and translation of psbA play an important role in high-light stress responses. A better understanding of the connection between chloroplast gene expression and environmental stress responses is crucial for breeding stress-tolerant crops better able to cope with the rapidly changing environment.

Light is essential for photosynthesis but light levels that exceed an organism’s assimilation capacity can cause serious damage or even cell death. Plants and microalgae have developed photoprotective mechanisms collectively referred to as non-photochemical quenching to minimize such potential damage. One such mechanism is energy-dependent quenching (qE), which dissipates excess light energy as heat. Over the last 30 years, much has been learned about the molecular mechanism of qE in green algae and plants. However, the steps between light perception and qE represented a gap in our knowledge until the recent identification of light-signaling pathways that function in these processes in the green alga Chlamydomonas reinhardtii. In this review, we summarize the high light and UV-mediated signaling pathways for qE in Chlamydomonas. We discuss key questions remaining about the pathway from light perception to photoprotective gene expression in Chlamydomonas. We detail possible differences between green algae and plants in light-signaling mechanisms for qE and emphasize the importance of research on light-signaling mechanisms for qE in plants.

Artificially enhancing photosynthesis is critical for improving crop yields and fruit qualities. Nanomaterials have demonstrated great potential to enhance photosynthetic efficiency; however, the mechanisms underlying their effects are poorly understood. This study revealed that the electron transfer pathway participated in nitrogen-doped carbon dots (N-CDs)-induced photosynthetic efficiency enhancement (24.29%), resulting in the improvements of apple fruit qualities (soluble sugar content: 11.43%) in the orchard. We also found that N-CDs alleviated mterf5 mutant-modulated photosystem II (PSII) defects, but not psa3 mutant-modulated photosystem I (PSI) defects, suggesting that the N-CDs-targeting sites were located between PSII and PSI. Measurements of chlorophyll fluorescence parameters suggested that plastoquinone (PQ), the mobile electron carrier in the photosynthesis electron transfer chain (PETC), was the photosynthesis component that N-CDs targeted. In vitro experiments demonstrated that plastoquinone-9 (PQ-9) could accept electrons from light-excited N-CDs to produce the reduced plastoquinone 9 (PQH₂-9). These findings suggested that N-CDs, as electron donors, offer a PQ-9-involved complement of PETC to improve photosynthesis and thereby fruit quality. Our study uncovered a mechanism by which nanomaterials enhanced plant photosynthesis and provided some insights that will be useful in the design of efficient nanomaterials for agricultural/horticultural applications.

The plastid-encoded RNA polymerase serves as the principal transcription machinery within chloroplasts, transcribing over 80% of all primary plastid transcripts. This polymerase consists of a prokaryotic-like core enzyme known as the plastid-encoded RNA polymerase core, and is supplemented by newly evolved associated proteins known as PAPs. However, the architecture of the plastid-encoded RNA polymerase and the possible functions of PAPs remain unknown. Here, we present the cryo-electron microscopy structure of a 19-subunit plastid-encoded RNA polymerase complex derived from spinach (Spinacia oleracea). The structure shows that the plastid-encoded RNA polymerase core resembles bacterial RNA polymerase. Twelve PAPs and two additional proteins (FLN2 and pTAC18) bind at the periphery of the plastid-encoded RNA polymerase core, forming extensive interactions that may facilitate complex assembly and stability. PAPs may also protect the complex against oxidative damage and has potential functions in transcriptional regulation. This research offers a structural basis for future investigations into the functions and regulatory mechanisms governing the transcription of plastid genes.