“Leveraging brassinosteroids towards the next Green Revolution”

   Green revolution was one of the major turning point that changed the field of agriculture and agricultural research. Population was increasing in much faster rate than that of agriculture production. To cope up with this situation, Dr. Norman. E. Borlaug around the world and Dr. M.S. Swaminathan in India, revolutionized agriculture in 1960s. Unintentionally, it was focused on the genes controlling gibberlin (GA). This led to breed dwarf varieties of crops, resulting in increase in global grain yield. However, GA function reduced nitrogen use efficiency, in turn resulting in significant environmental consequences. There are many phytohormones which regulate most of the plant traits and among them brassinosteroids (BRs) are the most crucial target for the next green revolution. BRs are polyhydroxylated steroidal phytohormones which are directly involved in the growth, and development and indirectly in productivity of plants. These were discovered in pollens of Brassica napus in the year 19791. Currently, three pathways (non-mevalonate pathway, mevalonate pathway and sterols pathway) of BR biosynthesis leading to the production of BRs. BR signalling and recognition has been studied in rice and it predominately involves the OsBRI1 in conjugation with co-receptor SERK-family protein (OsSERKs) located on cell membrane. The signal is subsequently transmitted downstrem through range of protein families, including BSK kinase (OsBSKs), PPKL phosphatase (OsPPKL), GSK3/ SHAGGY-like kinases (OsGSKs) and BZR-family transcription factors (OsBZRs)4. Signalling pathway mostly involve processes like acetylation, ubiquitination and phosphorylation to activate or suppress BR signals.

BRs are known to be involved in regulating many agronomic traits like plant height, grain size, fruit shape, leaf angle, tiller number, stress tolerance and many others. When stress tolerance is considered, BRs signaling genes are utilized for disease tolerance as it regulates JA signaling in plants2. In case of pest tolerance, the BR synthesised by plants when ingested by insect pest will tune gastatory receptor which in turn provides tolerance by acting as deterrent3. Eventhough it regulates many important traits, BRs exert pleiotropic effects on plants and thus present both opportunities and challenges for their application. As BRs regulate a spectrum of crop traits it paves the path to improve traits in crops that have attained saturation.

Accordingly, strategies that can be used for leveraging BRs regulation for crop improvement are exploring function-specific genes, identify beneficial alleles, induce favourable mutation and optimizing spatial hormone distribution4. The genes that regulate BRs synthesis and signaling have the potential to replace genes that regulate other phytohormones and in turn can be exploited to fully tap the potential of the crops under cultivation to usher next green revolution.

References:

1. GROVE, M.D., SPENCER, G.F., ROHWEDDER, W.K., MANDAVA, N., WORLEY, J.F., WARTHEN JR, J.D., STEFFENS, G.L., FLIPPEN-ANDERSON, J.L. AND COOK JR, J.C., 1979. Brassinolide, a plant growth-promoting steroid isolated from Brassica napus pollen. Nature, 281(5728): 216-217.

2. HE, Y., HONG, G., ZHANG, H., TAN, X., LI, L., KONG, Y., SANG, T., XIE, K., WEI, J., LI, J. AND YAN, F., 2020, The OsGSK2 kinase integrates brassinosteroid and jasmonic acid signaling by interacting with OsJAZ4. Plant Cell, 32(9): 2806-2822.

3. YANG, K., GONG, X.L., LI, G.C., HUANG, L.Q., NING, C. AND WANG, C.Z., 2020, A gustatory receptor tuned to the steroid plant hormone brassinolide in Plutella xylostella (Lepidoptera: Plutellidae). Elife, 9: 64114.

4. YANG, Y., CHU, C., QIAN, Q. AND TONG, H., 2023. Leveraging brassinosteroids towards the next Green Revolution. Trends Plant Sci.