Chloroplasts belong to a family of cell organelles called plastids, characteristic of organisms that perform photosynthesis. This process, which is essential for life on Earth, takes place in the chloroplasts, which give plants their characteristic green color through the accumulation of chlorophyll.These cellular organelles of plants and algae develop from proplastids present in germinating seeds and in young seedlings exposed to light. In addition to chloroplasts, plastids can differentiate to chromoplasts, which accumulate yellow and orange pigments that color fruits and flowers. The transition to chloroplasts and chromoplasts is highly regulated and very complex, as the researcher explains: “We take for granted that plants are green, lemons are yellow, and tomatoes are red, but this is the result of a very complex molecular transition about which we still know very little.”

Despite recent advances, the molecular mechanisms regulating biogenesis and differentiation remain poorly understood. Studying plants with differences in chloroplast development at the cellular level using novel omics technologies, and identifying epigenetic mechanisms, will help not only to understand the process but also to develop tools to combat climate change.

The review, conducted by Ramon y Cajal researcher Tamara Hernández-Verdeja of the CBGP's ‘Molecular bases of plant developmental phase transitions’ group, presents the molecular mechanisms that regulate chloroplast and chromoplast biogenesis and highlights aspects about which information is still lacking. Understanding how chloroplasts and chromoplasts develop will help generate biotechnological tools to combat climate change.

The key: differentiating cell types

New regulators of chloroplast biogenesis and chromoplast differentiation have recently been identified and are presented in this review. However, these studies of chloroplast development have been conducted in juvenile plants, without differentiating cell types.

This is important because plants with a more efficient and resilient type of photosynthesis develop chloroplasts in bundle branch cells, unlike most plants. Studies to date have focused on transcriptional regulation, and only recently has the role of epigenetics in the process been revealed. Furthermore, chromoplast differentiation still remains poorly understood.