Brassinosteroid
Brassinosteroids (BRs) are a class of polyhydroxylated steroidal phytohormones recognized as the sixth class of plant hormones, following auxin, gibberellins, cytokinin, abscisic acid, and ethylene[1][9]. They are structurally similar to animal steroid hormones and are essential for plant growth, development, and immunity[1]. BRs regulate a wide range of physiological processes, including cell elongation, cell division, root growth, photomorphogenesis, stomatal and vascular differentiation, seed germination, and reproduction[1]. They also play roles in plant responses to various stresses, such as freezing, drought, salinity, disease, heat, and nutrient deficiency[1][2].
BRs were first discovered in the 1970s when Mitchell and colleagues extracted growth-promoting substances from Brassica pollen, which led to the identification of brassinolide as the active component[1]. There are nearly 70 known natural brassinolide analogues isolated from various plant species[1].
Chemically, BRs are classified based on their side chain structures as C27, C28, or C29 steroids[1]. The most active BR identified to date is brassinolide, which has a 5α-cholestane skeleton with specific hydroxyl groups and a ketone or oxaketone system[1]. BRs are found in all parts of plants, with the highest concentrations in pollens, immature seeds, roots, and flowers, and they function in a paracrine or autocrine manner[1].
BR biosynthesis genes are widespread in various plant tissues, and BRs do not move between tissues but can have long-distance effects through crosstalk with other hormones like auxins and gibberellins[1]. The signaling pathway of BRs involves the detection of BRs by cell surface receptors, leading to a series of phosphorylation events that activate transcription factors in the nucleus, which then regulate BR-responsive genes[2].
BRs have been shown to have a positive impact on plant responses to various biotic and abiotic stresses, and their role in plant development and stress coping has been a subject of increasing interest[2]. The understanding of BR biosynthesis and signaling has been greatly advanced, particularly in Arabidopsis thaliana, providing a comprehensive view of BR synthesis and its signaling pathways[4][12].
In summary, brassinosteroids are vital plant hormones that play multifaceted roles in plant growth, development, and stress responses, and they have potential applications in agriculture to enhance crop yield and stress tolerance[1][2][10].
Citations:
[1] https://bmcbiol.biomedcentral.com/articles/10.1186/s12915-016-0340-8
[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8835148/
[3] https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2015.00950/full
[4] https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.01034/full
[5] https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/brassinosteroid
[6] https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.608061/full
[7] https://academic.oup.com/plcell/article/32/2/295/6099060
[8] https://www.nature.com/articles/s41477-021-00917-x
[9] https://en.wikipedia.org/wiki/Brassinosteroid
[10] https://link.springer.com/article/10.1007/s10725-020-00647-8
[11] https://journals.biologists.com/dev/article/146/5/dev151894/48995/Brassinosteroid-signaling-in-plant-development-and
[12] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7358554/
[13] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7037687/
[14] https://biolres.biomedcentral.com/articles/10.1186/s40659-018-0195-2
[15] https://www.sciencedirect.com/science/article/pii/S0981942899800412
[16] https://www.sciencedirect.com/topics/medicine-and-dentistry/brassinosteroid
[17] https://www.nature.com/articles/s41477-019-0436-6
[18] https://byjus.com/neet/brassionosteroids/
[19] https://en.wikipedia.org/wiki/Brassinolide
[20] https://www.collinsdictionary.com/us/dictionary/english/brassinosteroid