Strigolactones

The strigolactones are a group of natural and synthetic plant hormones . They prevent shoot branching , promote mycorrhization of the roots and induce the germination of the parasitic plant genus Striga . It is precisely because of these unrelated functions within the plant that the strigolactones were classified as plant hormones at a late stage.

synthesis

Strigolactones are a relatively small group of substances . The naturally present strigolactones are derived from the precursor 5-Deoxystrigol. This precursor in turn is produced via the β-carotene synthesis pathway. The place of this synthesis is inside the plastids , while the strigolactones are formed outside. The stage between these two places of synthesis has not yet been discovered. Auxins , which also suppress branch branching, have a positive influence on the synthesis of strigolactones.

Signal path

The genes MAX2, D3 and RMS4 code for F-box-like proteins , which are considered to be receptors for strigolactones. Similar receptors have already been discovered for auxin and jasmonate . It is believed that the Striga plant genus has a similar receptor.

effect

Strigolactones prevent shoot branching, promote mycorrhization of the roots and induce the germination of the parasitic plant genus Striga . The branching of the plant in particular has great economic potential, since the incidence of light, the distribution of flowers and seeds and the synchronous flowering and ripening can be controlled. This potential could be exploited through breeding programs with strigolactone mutants . In addition, research is being carried out into growth regulators which have an effect on branching but not on mycorrhization. The effect on sprout formation can be explained by the suppression of the polar auxin transporter (PAT) by strigolactones. The formation of shoots is ultimately suppressed by the hindered removal of auxin from the cells and the associated increased auxin concentration. Plants that are undersupplied with phosphate show increased concentrations of strigolactones. This leads to less branched plants with an improved root system and increased mycorrhization, which among other things can release immobile phosphates from the soil.

Methods against Striga parasitism

The Striga plant genus is the single largest biotic cause of crop loss in all of Africa . The financial damage is around 10 billion US dollars. Around 70 million hectares of arable land are considered Striga- contaminated. Various attempts are therefore being made to combat Striga parasitism. Thus, prior to sowing strigolactones sprayed the crops to a premature expulsion of Striga to induce. If there is no contact with the crop, the plant parts that are sprouted die and the nutrient reserves are used up. Sufficient fertilization of the cultivated area, especially with phosphate, has another effect , as this means that the production of strigolactones in the host plants is lower than on undersupplied soils. There is also a biotechnological approach based on gene transfer : a saturated isomer of the strigolactone GR24 continues to promote mycorrhization, but has no influence on the germination rate of Striga plants. If this isomer could be incorporated into the plant, there would be no induction of Striga parasitism.

chemistry

(+) - Strigol	(+) - strigyl acetate
(+) - Orobanchol	(+) - orobanchyl acetate
(+) - 5-Deoxystrigol	Sorgolactone

Individual evidence

1. ↑ Matusova, R., Rani, K., Verstappen, FWA, Franssen, MCR, Beale, MH, and Bouwmeester, HJ (2005): The strigolactone germination stimulants of the plant-parasitic Striga and Orobanche spp. are derived from the carotenoid pathway. Plant Physiol, 139, 920-934.
2. ↑ ^{a b c} Umehara, M., Hanada, A., Yoshida, S., Akiyama, K., Arite, T., Takeda-Kamiya, N., Magome, H., Kamiya, Y., Shirasu, K. , Yoneyama, K., Kyozuka, J., and Yamaguchi, S. (2008): Inhibition of shoot branching by new terpenoid plant hormones. Nature 455, 195-200.
3. ↑ Thimann, KV, and Skoog, F. (1934): On the inhibition of bud development and other functions of growth substance in Vicia faba. Proc. Roy. Soc. B. 114, 317-339.
4. ↑ Hayward, A., Stirnberg, P., Beveridge, C., and Leyser, O. (2009): Interactions between auxin and strigolactone in shoot branching control. Plant Physiol. 151, 400-412.
5. ↑ Johnson, X., Brcich, T., Dun, EA, Goussot, M., Haurogne, K., Beveridge, CA, and Rameau, C. (2006): Branching genes are conserved across species. Genes controlling a novel signal in pea are coregulated by other long-distance signals. Plant Physiol. 142, 1014-1026.
6. ↑ McSteen, P. (2009). Hormonal regulation of branching in grasses. Plant Physiol. 149, 46-55.
7. ↑ Akiyama, K., Matsuzaki, K.-i., and Hayashi, H. (2005): Plant sesquiterpenes induce hyphal branching in arbuscular mycorrhizal fungi. Nature 435, 824-827.
8. ↑ Bennett, T., Sieberer, T., Willett, B., Booker, J., Luschnig, C., and Leyser, O. (2006): The Arabidopsis MAX pathway controls shoot branching by regulating auxin transport. Curr. iol. 16, 553-563.
9. ↑ Umehara, M., Hanada, A., Magome, H., Takeda-Kamiya, N., and Yamaguchi, S. (2010): Contribution of strigolactones to the inhibition of tiller bud outgrowth under phosphate deficiency in rice. Plant Cell Physiol. 51, 1118-1126.
10. ↑ Ejeta, G. and Gressel, J. (eds) (2007): Integrating new technologies for striga control: towards ending the witch-hunt. World Scientific Publishing, Singapore.
11. ↑ Akiyama, K., Ogasawara, H., Ito, S. and Hayashi, H. (2010): Structural requirements of strigolactones for hyphal branching in AM fungi. Plant Cell Physiol., 51, 1104-1117.
12. ↑ Humphrey AJ, Beale MH. (2006): Strigol: biogenesis and physiological activity. Phytochemistry, 67 (7), 636-40.