Phytochrome chromophore deficiency leads to overproduction of jasmonic acid and elevated expression of jasmonate-responsive genes in Arabidopsis

An Arabidopsis mutant line named hy1- 101 was isolated because it shows stunted root growth on medium containing low concentrations of jasmonic acid ( JA). Subsequent investigation indicated that even in the absence of JA, hy1- 101 plants exhibit shorter roots and express higher levels of a group of JA- inducible defense genes. Here, we show that the hy1- 101 mutant has increased production of JA and its jasmonate- related phenotype is suppressed by the coil-1 mutation that interrupts JA signaling. Gene cloning and genetic complementation analyses revealed that the hy1- 101 mutant contains a mutation in the HY1 gene, which encodes a heme oxygenase essential for phytochrome chromophore biosynthesis. These results support a hypothesis that phytochrome chromophore deficiency leads to overproduction of JA and activates COI1- dependent JA responses. Indeed, we show that, like hy1- 101, independent alleles of the phytochrome chromophore- deficient mutants, including hy1- 100 and hy2 ( CS68), also show elevated JA levels and constant expression of JA- inducible defense genes. We further provide evidence showing that, on the other hand, JA inhibits the expression of a group of light- inducible and photosynthesis- related genes. Together, these data imply that the JA- signaled defense pathway and phytochrome chromophore- mediated light signaling might have antagonistic effects on each other.