Biological complexity:pest plant steals water and nurients (Introduction)

by David Turell , Monday, February 25, 2019, 20:36 (2098 days ago) @ David Turell

Witchweed in Africa steals from crops with complex controls from mutations:

https://phys.org/news/2019-02-secret-witchweed-devastating-ability-nutrients.html

"Striga hermonthica is a parasitic weed mainly found in the African continent south of the Sahara desert. It leeches off the roots of major cereal crops such as sorghum, millet, sweetcorn and rice, absorbing water and nutrients from its hosts.

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"When plants are subjected to drought stress, they synthesize a plant hormone called abscisic acid (ABA). This small molecule elicits stomata closure to suppress transpiration. Striga leaves contain a large amount of ABA, and exogenous ABA treatment did not reduce transpiration. The team concluded that the cause of Striga's high transpiration levels is a defectiveness in ABA sensitivity.

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"ABA in plants rapidly increases in response to drought stress and binds a receptor known as PYL. The ABA-bound PYL receptor complex binds and inhibits group-A type-2 C protein phosphatases (PP2Cs), which are negative regulators for ABA signaling. Consequently, inhibition of PP2Cs enable guard cells to close stomata (Figure 3). The research group isolated relevant genes in Striga and analyzed their functions. They identified the ShPP2C1 gene, and its protein blocked the signaling of ABA constitutively, because ShPP2C1 is not controlled by PYL receptors (Figure 3). ShPP2C1 has distinct amino acid mutations not seen in other plants. When the team edited five amino acid sequences in model plant Arabidopsis to resemble ShPP2C1 (represented as AtABI15 mutation), the Arabidopsis' response to ABA decreased, and its high transpiration levels remained even under drought conditions

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"Professor Sugimoto and Assistant Professor Okamoto comment: "Our results show that amino acid mutations changed the properties of PP2C genes in Striga, lowering its sensitivity to ABA and allowing it to maintain high transpiration rates even under drought conditions.
Terrestrial plants acquired ABA signaling in order to survive in an environment with changing water conditions. Striga probably lost these functions and acquired its own nutrient acquisition methods in the process of adapting to its parasitic lifestyle."

Comment: This study simply shows how complex adaptations can be as molecular reactions are modified to reduce defenses. Not by chance.