An activation-tagged allele of activated
disease resistance 1 (ADR1) has previously been shown to convey broad spectrum
disease resistance. ADR1 was found to encode a coiled-coil (CC)-
nucleotide-binding site (NBS)-
leucine-rich repeat (LRR)
protein, which possessed domains of homology with
serine/threonine protein kinases. Here, we show that either constitutive or conditional enhanced expression of ADR1 conferred significant drought tolerance. This was not a general feature of defence-related mutants because cir (constitutive induced resistance)1, cir2 and
cpr (constitutive expressor of PR genes)1, which constitutively express systemic acquired resistance (SAR), failed to exhibit this phenotype. Cross-tolerance was not a characteristic of adr1 plants, rather they showed increased sensitivity to thermal and salinity stress. Hence, adr1-activated signalling may antagonise some stress responses. Northern analysis of abiotic marker genes revealed that
dehydration-responsive
element (DRE)B2A but not DREB1A, RD (response to
dehydration)29A or RD22 was expressed in adr1 plant lines. Furthermore, DREB2A expression was
salicylic acid (SA) dependent but NPR (non-expressor of PR genes)1 independent. In adr1/ADR1 nahG (
naphthalene hydroxylase G), adr1/ADR1 eds (enhanced
disease susceptibility)1 and adr1/ADR1 abi1 double mutants, drought tolerance was significantly reduced. Microarray analyses of plants containing a conditional adr1 allele demonstrated that a significant number of the upregulated genes had been previously implicated in responses to
dehydration. Therefore, biotic and abiotic signalling pathways may share multiple nodes and their outputs may have significant functional overlap.