Evolutionary and functional significance of ShPP2C1 in the parasitic life strategy of <i>Striga</i>

Parasitic plants have evolved specialized mechanisms to extract water and nutrients from their hosts, often causing severe agricultural losses. Striga hermonthica, a member of the Orobanchaceae family, exhibits a unique adaptation in the abscisic acid (ABA) signaling pathway, which enhances its growth efficiency during parasitism. Striga hermonthica protein phosphatase 2C (ShPP2C1) is a negative regulator of ABA signaling but, unlike typical PP2Cs, is not inhibited by PYR1-like (PYL) ABA receptors. Because of ShPP2C1, Striga hermonthica shows low ABA sensitivity and high transpiration, facilitating resource uptake from the host. To determine whether similar PP2Cs are conserved in other parasitic Orobanchaceae, we performed a phylogenetic analysis using public sequence data, revealing that ShPP2C1 is unique to the genus Striga. Furthermore, an in vitro phosphatase assay revealed specific amino acid residues responsible for disrupting the inhibition by PYLs. Structural comparisons between ShPP2C1 and Arabidopsis ABA INSENSITIVE 1 (ABI1) showed that the lack of interaction with PYLs is due to steric hindrance from a combination of amino acid substitutions. These findings provide new insight into the molecular basis of Striga's parasitic strategy.