Abstract
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 phot1 mutants in Arabidopsis thaliana. The double mutant phot1 lea1 (leaf expansion associated 1), which is defective in cotyledon flattening and positioning but not the phototropic response was selected. This mutant phenotype could be alleviated by constitutively expressing MORE AXILLARY GROWTH 2 (MAX2), indicating that LEA1 was allelic to MAX2. The max2 mutants (max2-2 and max2-3) are defective in cotyledon flattening, which is similar to that of the phot1 phot2 mutants. Moreover, the amounts of MAX2 transcripts are inhibited in leaves of phot1 mutant. However, the additional disruption of PHOT1 gene in max2-2 or max2-3 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.
Highlights
Light provides energy and several environmental signals important for plant growth
Phot1 lea1 formed more rosette leaves in the vegetative stage (Figure 1D) and had increased shoot branching in the flowering stage (Figure 1E). These results indicated that LEA1 played an important role in leaf positioning and flattening
When treated with 30 μmol L−1 GR24, hypocotyl elongation was reduced in all genotypes investigated, the reductions in max2-2, max2-3, phot1 max2-2, and phot1 max2-3 were smaller than in wild type (WT), phot1, phot2, or phot1 phot2 (Figure 4B). These results indicated that MORE AXILLARY GROWTH 2 (MAX2) regulated the strigolactone-inhibited elongation of the hypocotyls, and that this was not affected by the disruption of PHOT1
Summary
Light provides energy and several environmental signals important for plant growth. The cotyledonary petiole angle, the angle between the cotyledonary petiole and the horizontal plane, and the cotyledon angle between the petiole and cotyledonary blade (Harada et al, 2013) can be determined in different growing conditions to better elucidate the regulation of leaf positioning and flattening. These processes were found to be mainly regulated by phot under weak white light, but by both phot and phot under moderate and strong levels of white light (Harada et al, 2013). These results demonstrated that numerous factors and pathways participate in the regulation of leaf positioning and flattening
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