Mutation of A rabidopsis CATALASE2 results in hyponastic leaves by changes of auxin levels

Auxin and H 2 O 2 play vital roles in plant development and environmental responses; however, it is unclear whether and how H 2 O 2 modulates auxin levels. Here, we investigate this question using cat2‐1 mutant, which exhibits reduced catalase activity and accumulates high levels of H 2 O 2 under photorespiratory conditions. At a light intensity of 150  μ mol m −2  s −1 , the mutant exhibited up‐curled leaves that have increased H 2 O 2 contents and decreased auxin levels. At low light intensities (30  μ mol m −2  s −1 ), the leaves of the mutant were normal, but exhibited reduced H 2 O 2 contents and elevated auxin levels. These findings suggest that H 2 O 2 modulates auxin levels. When auxin was directly applied to cat2‐1 leaves, the up‐curled leaves curled downwards. In addition, transformation of cat2‐1 plants with pCAT2 :iaa M , which increases auxin levels, rescued the hyponastic leaf phenotype. Using qRT ‐ PCR , we demonstrated that the transcription of auxin synthesis‐related genes and of genes that regulate leaf curvature is suppressed in cat2‐1 . Furthermore, application of glutathione rescued the up‐curled leaves of cat2‐1 and increased auxin levels, but did not change H 2 O 2 levels. Thus, the hyponastic leaves of cat2‐1 reveal crosstalk between H 2 O 2 and auxin signalling that is mediated by changes in glutathione redox status.