Abstract
To anticipate potential seedling damage, plants block seed germination under unfavorable conditions. Previous studies investigated how seed germination is controlled in response to abiotic stresses through gibberellic and abscisic acid signaling. However, little is known about whether seeds respond to rhizosphere bacterial pathogens. We found that Arabidopsis seed germination is blocked in the vicinity of the plant pathogen Pseudomonas aeruginosa. We identified L-2-amino-4-methoxy-trans-3-butenoic acid (AMB), released by P. aeruginosa, as a biotic compound triggering germination arrest. We provide genetic evidence that in AMB-treated seeds DELLA factors promote the accumulation of the germination repressor ABI5 in a GA-independent manner. AMB production is controlled by the quorum sensing system IQS. In vitro experiments show that the AMB-dependent germination arrest protects seedlings from damage induced by AMB. We discuss the possibility that this could serve as a protective response to avoid severe seedling damage induced by AMB and exposure to a pathogen.
Highlights
Seeds are remarkable structures promoting plant dispersal by preserving the plant embryo in a desiccated and highly resistant state
We explored whether Pseudomonas bacteria release compounds inhibiting Arabidopsis seed germination as follows: (1) individual Pseudomonas species were propagated for 3 days on germination agar medium supplemented with a carbon source; (2) thereafter Arabidopsis seeds were sown on the germination medium at various distances from the bacteria; (3) germination was scored after culturing seeds for 3 days (Materials and methods, Figure 1—figure supplement 1A)
We conclude that P. aeruginosa releases a germination repressive activity (GRA) that diffuses in the germination medium
Summary
Seeds are remarkable structures promoting plant dispersal by preserving the plant embryo in a desiccated and highly resistant state. Their appearance in the course of land plant evolution is regarded as a cornerstone of the striking spread and diversification of angiosperms among terrestrial plants. Seed imbibition with water is the necessary first step to permit germination, transforming the embryo into a fragile juvenile seedling. Plants have evolved control mechanisms that block germination under unfavorable conditions to maintain the highly protected embryonic state (Lopez-Molina et al, 2001; 2002). GA induces proteolysis of DELLA factors repressing germination, which are encoded by a family of five genes: RGL2, GAI, RGA, RGL1 and RGL3
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