Functional Analysis of MAX2 in Phototropins-Mediated Cotyledon Flattening in .

Phototropins (phot1 and phot2) are blue-light receptors that control cotyledon flattening and positioning under strong light; however, their functional redundancy restricts our understanding of the specific roles of phot2. To identify the factors responsible for phot2-dependent cotyledon flattening and growth, we screened for light-insensitive mutants among mutagenized mutants in . The double mutant (), which is defective in cotyledon flattening and positioning but not the phototropic response was selected. This mutant phenotype could be alleviated by constitutively expressing (), indicating that was allelic to . The mutants ( and ) are defective in cotyledon flattening, which is similar to that of the mutants. Moreover, the amounts of MAX2 transcripts are inhibited in leaves of mutant. However, the additional disruption of gene in or did not affect their phenotype, including MAX2-mediated inhibition of hypocotyl elongation. By contrast, phototropins-mediated hypocotyl phototropism was not regulated by MAX2. Together, these results suggest that cotyledon flattening was mediated by both phototropins and MAX2 signaling, but the relationship between two pathways need further study.