Chloroplast development in green plant tissues: the interplay between light, hormone, and transcriptional regulation

Chloroplasts are best known for their role in photosynthesis, but they also allow nitrogen and sulphur assimilation, amino acid, fatty acid, nucleotide and hormone synthesis. How chloroplasts develop is therefore relevant to these diverse and fundamental biological processes, but also to attempts at their rational redesign. Light is strictly required for chloroplast formation in all angiosperms and directly regulates the expression of hundreds of chloroplast-related genes. Light also modulates the levels of several hormones including brassinosteriods, cytokinins, auxins and gibberellins, which themselves control chloroplast development particularly during early stages of plant development. Transcription factors such as GOLDENLIKE1&2 (GLK1&2), GATA NITRATE-INDUCIBLE CARBON METABOLISM-INVOLVED (GNC) and CYTOKININ-RESPONSIVE GATA FACTOR 1 (CGA1) act downstream of both light and phytohormone signalling to regulate chloroplast development. Thus, in green tissues transcription factors, light signalling and hormone signalling form a complex network regulating the transcription of chloroplast- and photosynthesis-related genes to control the development and number of chloroplasts per cell. We use this conceptual framework to identify points of regulation that could be harnessed to modulate chloroplast abundance and increase photosynthetic efficiency of crops, and to highlight future avenues to overcome gaps in current knowledge.

Automated summary

Chloroplasts play a crucial role in photosynthesis and various biological processes including nitrogen and sulphur assimilation, amino acid, fatty acid, nucleotide and hormone synthesis. Light is essential for chloroplast formation and directly regulates the expression of chloroplast-related genes. Hormones such as brassinosteriods, cytokinins, auxins and gibberellins are also modulated by light and control chloroplast development during early stages of plant growth. Transcription factors, light signaling, and hormone signaling form a complex network regulating the transcription of chloroplast- and photosynthesis-related genes to control chloroplast development in green tissues.