Bacterial Quorum-Sensing Signaling-Related drr1 Mutant Influences Abscisic Acid Responsiveness in Arabidopsis thaliana L.

N-acyl-L-homoserine lactones (AHLs) are involved in cell-to-cell communication in Gram-negative bacteria through a process termed quorum-sensing (QS). In this report, we evaluated the response of Arabidopsis thaliana primary roots to abscisic acid (ABA) in wild-type (WT) and decanamide resistant root 1 (drr1) mutant, previously reported to be resistant to N-decanoyl-L-homoserine lactone (C10-HL). When compared to WT seedlings, drr1 mutants were hypersensitive to ABA and had primary roots shorter, which correlated with lower cell division in meristems, a higher concentration of endogenous ABA, and a greater expression of ABI5 gene; and this shortened primary root phenotype was reversed in drr1abi5 double mutants. An analysis of expression of ABSCISIC ACID INSENSITIVE 4 (ABI4) showed an ABA-inducible pattern in primary root tips, which was further increased in drr1 mutant seedlings. Comparison of seed germination in WT, drr1, abi5, and drr1abi5 lines showed higher germination percentages in the following order under control condition: abi5 > drr1abi5 > WT > drr1, while abi5 and drr1abi5 germinated faster and drr1 germinated slower with respect to WT under ABA condition. Taken together, our results suggest that DRR1 is a negative regulator of ABA signaling probably acting upstream of the transcription factors ABI4 and ABI5, which influence ABA responsiveness in primary roots and seed germination.