Auxin binding proteins ABP1 and ABP4 are involved in the light- and auxin-induced down-regulation of phytochrome gene PHYB in maize (Zea mays L.) mesocotyl

Abstract

Previous research in maize suggested a possible involvement of auxin-binding proteins (ABPs) in light signaling during maize seedling development. To obtain more information about the interaction of auxin and light signaling, we investigated the gene expression of phytochrome B (PHYB) and phytochrome A (PHYA) in loss-of-function mutants in ABP1 and ABP4 genes in maize (Zea mays L.). We studied how expression of the PHYB and PHYA genes in mesocotyl is regulated by white light (WL), and whether exogenous auxin NAA influences the expression of the phytochrome genes. We found that knockout of ABP1 or ABP4 results in essentially reduced expression of PHYB gene in dark-grown mesocotyl. WL reduced PHYB expression in WT but not in the ABPs knockout seedlings. The data indicate that ABP1 and ABP4 are positively involved in PHYB expression in etiolated mesocotyl. Our results also indicate that in etiolated mesocotyl, ABP1 and ABP4 mediate the inhibitory effect of exogenous auxin on level of PHYB transcript. In contrast, in our experimental conditions, WL does not reduce expression of PHYA. Our results further suggest that ABP1 and ABP4 are not likely involved in the expression of PHYA gene and neither in auxin-induced suppression of PHYA transcript accumulation. Our results support the existence of cross-talk between auxin and light signaling and indicate for the first time that ABP1, ABP4 and PHYB genes could share common signaling pathway(s).