Strigolactone
[3] The isolation of strigolactones lead to a series of tests that proved that this compound was the necessary molecule to induce germination of Striga species.
[3] Later on, similar compounds were proven to produce the same effect: sorgolactone and alectrol, both of them presented the characteristic lactone group, so they were classified as strigolactones.
[4] To induce germination of parasitic plants, strigolactones only needed to be present in trace amounts, in the order of 5 parts per million.
[5] These mutants presented excessive growth in the axillary buds, which induced their terminal stem to start branching abnormally.
[5] Different tests that consisted in inserting part of the mutants plants into wild specimens (and vice versa), were able to demonstrated that the mutants were either not able to recognize a signal molecule coming from the roots and the lower part of the plant, or not able to produce the require molecules to inhibit branching.
The balance between zealactone and two other strigolactones, zealactol and zealactonoic acid (ZA), can be altered by changes in flux through these pathways.
This discovery has implications for breeding Striga resistance in maize by modifying the strigolactone blend, potentially reducing the devastating effects of this parasitic weed in Africa.
The protein MAX1 has been proposed to catalyze the last step of the biosynthesis of strigolactones due its role in oxidative metabolism in plants.
[8] Both, abscisic acid (ABA) and strigolactones have a common group of enzymes that carried out the synthesis of the two compounds, previously it had been demonstrated the existence of a correlation of the two biosynthesis pathways, and it has been supported by different studies.
[10] But, mutants plants that were defective in the production of the NCED enzymes, not just presented low levels of ABA, rather they also present low levels of strigolactones, specifically in the roots extracts where this hormone is mostly synthesized, this finding provided the basis for the existence of a common enzymatic machinery,[10] Other experiments that consist in blocking the NCED enzymes and using mutants unable to detect ABA changes, were used to support this theory.
[9] So far there is a clear correlation of both synthesis that is related to the used of NCED enzymes in both biosynthesis, but the exact mechanism in which they are connected remains unclear.
Despite being considered hydrolases with poor substrate turnover, an intact catalytic triad is required for the protein's biological function.
[23] Different studies with diverse type of fungi, have found that after stimulation with strigolactones, the fungal cells present a higher amount of mitochondria and an increase in their oxidative activity.
[23] Due to the role of mitochondria in oxidative metabolism of macronutrients, it is thought that the spores remain inactive before finding the host plant, and once they are stimulated with strigolactones, the oxidative machinery in the mitochondrion gets activated to produce energy and nutrients necessaries for germination of the spore and fungal branching.
[23] Studies with root extracts support this hypothesis, and so far strigolactones are the candidate molecules that better explain this increased in mitochondrial activity.
[24] Thus, it was not surprising that when analyzing strigolactone deficient mutants, they were found to present an over-expression of PIN1 protein, which facilitate the transport of auxin in the terminal buds; auxin prevented the mitotic activity of these buds, stopping the plant to initiate secondary growth and branching.
[25] Because arbuscula mychorriza can form symbiotic associations with the majority of the angiosperms, and many gymnosperms, it is expected to found different strigolactones compounds distributed in a whole variety of plants.
[27] When these Myc factors are recognized by the plant's root, they stimulate the expression of different genes involved in the initiation of the symbiotic association.
[28] Providing adequate phosphate through soil fertilization has been proved to reduce the proliferation of these parasites, because they require strigolactone for its germination.
