Understanding Gene Evolution in Fat Storage of Major Oilseed Crops

Jenn Hoskins
4th July, 2024

Understanding Gene Evolution in Fat Storage of Major Oilseed Crops

Image Source: Natural Science News, 2024

Key Findings

  • The study by ICAR-Indian Institute of Seed Science focused on lipid droplets in major oilseeds to understand gene selection and improve seed oil content and germination
  • Positive selection was the main force driving the evolution of 94 genes, including oleosin and TAG-lipases, enhancing lipid metabolism and seed germination
  • Species-specific differences in selection pressures were observed, with significant positive selection in oil palm LOX genes and deleterious mutations in Arachis hypogaea oleosins
Seed germination and early seedling growth rely heavily on the energy stored within lipid droplets (LDs) in the cytosol of seeds. These LDs serve as the subcellular storage compartments for lipids and are crucial for providing the necessary energy for germinating seeds. Understanding how natural selection influences the genes associated with these lipid droplets can provide insights into improving seed oil content and germination efficiency. A recent study conducted by the ICAR-Indian Institute of Seed Science aimed to predict selection signatures among orthologous clades in major oilseeds and to correlate these selection effects with gene expression[1]. Lipid droplets are essential for seed endurance and are found across various plant species, including algae, where they increase during stress conditions[2]. The proteins associated with LDs, such as lipoxygenases, phospholipase D, oleosins, TAG-lipases, steroleosins, caleosins, and SEIPINs, play significant roles in facilitating germination and enhancing lipid metabolism. However, the balance between these processes and how natural selection influences them remains unclear. The study analyzed LD-associated genes from major oil-bearing crops to predict natural selection signatures and understand adaptive evolution. The researchers found that positive selection was the primary force driving the evolution and diversification of orthologs in a lineage-specific manner. Specifically, 94 genes, including oleosin and TAG-lipases, showed significant positive selection effects. In contrast, 44 genes were under purifying selection with an excess of non-synonymous substitutions, and 35 genes were neutral to selection effects. Interestingly, the study revealed species-specific differences in selection pressures. For example, in Brassicaceae, no significant selection impact was observed, whereas LOX genes in oil palm showed considerable positive selection. Additionally, deleterious mutations affecting selection signatures were detected in T-lineage oleosins and LOX genes of Arachis hypogaea. These T-lineage oleosin genes were primarily involved in anther, tapetum, and anther wall morphogenesis. Further findings indicated that in Ricinus communis and Sesamum indicum, over 85% of phospholipase D (PLD) genes were under selection, whereas selection pressures were lower in Brassica juncea and Helianthus annuus. Steroleosin, caleosin, and SEIPINs, which play significant roles in lipid droplet organization, were mostly expressed in seeds and were under considerable positive selection pressures. Expression divergence among paralogs and homeologs was also evident, with one gene often attaining functional superiority over the other. A notable observation was the expression pattern of the LOX gene Glyma.13g347500, associated with off-flavor, which was not expressed during germination. Instead, its paralog Glyma.13g347600 showed expression in Glycine max. This finding suggests that natural selection may favor genes that enhance seed quality by reducing undesirable traits such as off-flavors. The study also highlighted the expression patterns of different PLD genes. PLD-α genes were expressed in all tissues except the seed, δ genes were expressed in seeds and meristems, while β and γ genes were primarily expressed in leaves. These findings suggest that different PLD genes may have specialized roles in various tissues, contributing to the overall lipid metabolism and storage in seeds. The results of this study build on previous research that has identified key regulators of lipid metabolism in microalgae under stress conditions[3]. For instance, the MYB1 transcription factor in Chlamydomonas reinhardtii was found to promote lipid accumulation by facilitating fatty acid transport from the chloroplast to the endoplasmic reticulum. This regulatory mechanism may share similarities with the processes observed in seed lipid metabolism, where specific genes are under positive selection to enhance lipid storage and utilization. Additionally, the study provides a broader context to the dynamic nature of lipid droplets, as highlighted in earlier research[4]. Lipid droplets are not just static storage depots but are dynamic organelles with diverse functions across different organisms. The identification of new LD-associated proteins and the comparative analysis of their expression during various developmental phases in Arabidopsis further emphasize the complexity and adaptability of lipid droplets[5]. In conclusion, this study by the ICAR-Indian Institute of Seed Science identifies key genes under positive selection that enhance seed oil content and germination efficiency. By understanding the adaptive evolution of these genes, researchers can develop strategies to improve crop yields and seed quality, ultimately benefiting agricultural practices and food production.

GeneticsPlant ScienceEvolution

References

Main Study

1) Exploring selection signatures in the divergence and evolution of lipid droplet (LD) associated genes in major oilseed crops.

Published 1st July, 2024

https://doi.org/10.1186/s12864-024-10527-4

Related Studies

2) Ties between Stress and Lipid Droplets Pre-date Seeds.

https://doi.org/10.1016/j.tplants.2020.07.017

3) The Chlamydomonas transcription factor MYB1 mediates lipid accumulation under nitrogen depletion.

https://doi.org/10.1111/nph.18141

4) Lipid droplets throughout the evolutionary tree.

https://doi.org/10.1016/j.plipres.2020.101029

5) Identification of Low-Abundance Lipid Droplet Proteins in Seeds and Seedlings.

https://doi.org/10.1104/pp.19.01255


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