The bakanae fungus F. fujikuroi has spread widely over the world’s rice-growing regions, appearing in both tropical and temperate environments. Bakanae is One of the first rice diseases to be officially identified, and it causes production losses ranging from 3.0-95.4% depending on the location and cultivars produced1. The main region of this Bakane disease (the other name is The foolish seedling) is Japan. Bakane disease was caused by the infection of the Oryza sativa rice plant by the Gibberella fujikuroi pathogen2. That’s why the first studies were done by Japan and the surrounding countries. The fact that Japan is closed to the outside has negatively affected the awareness of these studies abroad. The USA and the United Kingdom were included in these studies when Japan opened up to the outside world after World War II. Gibberella fujikuroi infection was thought to be the cause of the disease, and Kurosawa’s research in 1926 revealed that applying fungal extracts to healthy plants caused the same symptoms as Bakanae disease. The active component from the fungal extract was isolated by Yabuta and Hayashi and given the name gibberellin(GA) in the 1930s.GAs was first isolated as ‘‘phytotoxic” metabolites of a fungal rice pathogen3(pp171–190). This fungus was extremely useful in understanding the nature and metabolic genesis of GAs. Researches about the life cycle of the interesting fungi involved in the discovery of gibberellin are as follows.

In research for precautions against this fungus, it was learned that an extract from this fungus produces an unusual stem extension in rice plants, which is a symptom of ministerial (foolish seedling) disease. It is characterized by severe stem elongation and sterility or reduced rice production. Gibberellin was named for the active component that was identified from the extract. On the coat of infected seeds, the virus is known to overwinter as spores. There is the little amount of proof that seeds get infected inside. Grain with a severe infection may seem discolored. While infected seeds without discoloration generate seedlings with the normal signs of Bakanae, discolored seeds result in stunted seedlings. Infection may also take place through spores and mycelium, which are left in the water used for soaking seeds. Ascospores and conidia adhering to the seed germinate and infect seedlings through the roots and crown. The fungus becomes systemic within the plant but does not enter the floral parts4 (Figure 1). Fusarium moniliforme is the other name given to Gibberella fujikuroi when its sexual form is disregarded.
The mevalonic acid route (MVA pathway) and the basic isoprenoid unit isopentenyl diphosphate are used to synthesize fungal GAs from acetyl-CoA. (IPP). GA biosynthesis diverges from the main terpenoid biosynthetic route at the farnesyl diphosphate step (FDP). Geranylgeranyl diphosphate (GGDP), the next step, is produced by two distinct GGDP synthases, GGS1 and GGS2. The GA pathway-specific GGDP synthase, GGS2, is the only enzyme capable of producing the GGDP required for GA biosynthesis. Most bioactive GAs produced from this biosynthesis are GA1, GA3, GA4, and GA7. Gibberella fujikuroi induces the production of GA3, one of the bioactive GAs, in the plant it infects. This helped to find gibberellin in studies on the Bakanae disease5.

Gibberellic acid (GA3) was found to be structurally similar to gibberellin A3 at the ICI Laboratories in the United Kingdom. Then, in the middle of the 1950s, British researchers found that GAs are naturally occurring controls on higher plant growth and development. After it was learned that GAs may affect a variety of plant developmental processes, high-GA titer mutants of the fungus G. fujikuroi were used to produce these plant hormones on a global scale. Presently, 136 GAs, designated GA1 to GA136 in order of discovery, are known from plants, fungi, and even bacteria. Only a few of them, including GA1 and GA4, are believed to function as hormones in plants5. The potential of gibberellic acid to rescue dwarf mutants of maize and pea as well as to cause bolting and blooming in rosette species was discovered to have major impacts on plant development. With the help of the earlier studies, we can use our method of getting gibberellin from G. fujikuroi to give these treatments6.
References:
- Gupta AK, Solanki IS, Bashyal BM, Singh Y, Srivastava K. Bakanae of rice -An emerging disease in Asia. J Anim Plant Sci. 2015;25(6).
- Cerdá-Olmedo E, Fernández-Martín R, Ávalos J. Genetics and gibberellin production in Gibberella fujikuroi. Antonie Van Leeuwenhoek. 1994;65(3). doi:10.1007/BF00871950
- Srivastava LM. Gibberellins. In: Plant Growth and Development. ; 2002. doi:10.1016/b978-012660570-9/50148-9
- Barkley PB, Beattie G a C. Contingency Plans for Hlb ( Huanglongbing ) and His Vectors in Australia. Flora. 2008;(2002).
- Bömke C, Tudzynski B. Diversity, regulation, and evolution of the gibberellin biosynthetic pathway in fungi compared to plants and bacteria. Phytochemistry. 2009;70(15-16). doi:10.1016/j.phytochem.2009.05.020
- Hedden P, Sponsel V. A Century of Gibberellin Research. J Plant Growth Regul. 2015;34(4). doi:10.1007/s00344-015-9546-1
Figure References:
- Bömke C, Tudzynski B. Diversity, regulation, and evolution of the gibberellin biosynthetic pathway in fungi compared to plants and bacteria. Phytochemistry. 2009;70(15-16). doi:10.1016/j.phytochem.2009.05.020
- Trail F. For blighted waves of grain: Fusarium graminearum in the postgenomics era. Plant Physiol. 2009;149(1):103-110. doi:10.1104/pp.108.129684
Inspector: Meryem Melisa KAR