Research Projects

Key cellular activities such as cell division, expansion, and fate-determination, coupled with the biogenesis of the subcellular organelles within, regulate the development of organs to their functional mature forms. Regulation of the cellular processes and the subcellular processes have always been studied individually, and a link between them has been ignored. This question is especially important in leaf development, since leaves are the primary chloroplast-containing organs specialized for photosynthesis and energy capturing. Leaf morphogenesis is usually characterized by cell proliferation at the base and a progressively increasing differentiation and expansion towards the tip¹. Our earlier work on wheat leaves showed that the transition from cell proliferation to expansion involves proliferation and maturation of early plastids into the photosynthetic chloroplasts². This suggests that there is a synchrony between cell morphogenesis and chloroplast development, a link that is perhaps important for the overall leaf development, a perturbation of which may result in malformed leaves³. To test this, we need to isolate and study mutants showing defects in both chloroplast and leaf development. A large-scale activation tagging⁴ mutagenesis of the chloroplast-defective glk1 glk2 (golden2-like) double mutant⁵ yielded a novel mutant named golden to green9-D (gog9-D) with altered leaf morphology (curled) and enhanced greening (Fig. 1B and 1C), providing an opportunity to uncover the connection between organ morphogenesis and chloroplast development. The current study aims to identify the GOG9 gene and characterize its function in chloroplast development and leaf development⁶. Rationale of the research: Preliminary analysis suggest that chloroplast development enhanced and leaf form altered in the dominant gog9-D mutant, suggesting that the GOG9 product couples organ morphogenesis and chloroplast maturation in Arabidopsis. Further investigation would uncover the molecular link between chloroplast biogenesis and its association with leaf development (Fig 1 and 2). Questions to be addressed: • How are chloroplast maturation and leaf differentiation interconnected? • How does chloroplast development impact leaf morphology? • Are there common regulators of chloroplast development and organ morphogenesis? Significance: As gog9-D shows improved chloroplast development with altered leaf phenotype, this study would identify the candidate genes that coordinate organelle and cell development. Moreover, this study may uncover the critical players that determine chloroplast occupancy in photosynthetic cell and shape of a leaf. References: 1. Vercruysse et al. (2020), J. Exp. Bot., 71(8), 2365–78. 2. Loudya, Mishra et al. (2021), Genome Biol., 22, 1–30. 3. Andriankaja et al. (2012), Dev. Cell, 22, 64–78. 4. Weigel et al. (2000), Plant Physiol., 122, 1003–14. 5. Fitter et al. (2002), Plant J., 31, 713–27. 6. Nath et al. (2003), Science, 299, 1404–7.