Maize cryptochromes 1a1 and 1a2 promote seedling photomorphogenesis and shade resistance in Zea mays and Arabidopsis

Maize growth and development are regulated by light quality, intensity and photoperiod. Cryptochromes are blue/ultraviolet-A light receptors involved in stem elongation, shade avoidance, and photoperiodic flowering. To investigate the function of cryptochrome 1 (CRY1) in maize, where it is encoded by ZmCRY1, we obtained two ZmCRY1a genes (ZmCRY1a1 and ZmCRY1a2), both of which share the highest similarity with other gramineous plants, in particular rice CRY1a by phylogenetic analysis. In Arabidopsis, overexpression of ZmCRY1a genes promoted seedling de-etiolation under blue and white light, resulting in dwarfing of mature plants. In seedlings of the maize inbred line Zong 31 (ZmCRY1a-OE), overexpression of ZmCRY1a genes caused a reduction in the mesocotyl and first leaf sheath lengths due to down-regulation of genes influencing cell elongation. In mature transgenic maize plants, plant height, ear height, and internode length decreased in response to overexpression of ZmCRY1a genes. Expression of ZmCRY1a were insensitive to low blue light (LBL)-induced shade avoidance syndrome (SAS) in Arabidopsis and maize. This prompted us to investigate the regulatory role of the gibberellin and auxin metabolic pathways in the response of ZmCRY1a genes to LBL treatment. We confirmed a link between ZmCRY1a expression and hormonal influence on the growth and development of maize under LBL-induced SAS. These results reveal that ZmCRY1a has a relatively conservative function in regulating maize photomorphogenesis and may guide new strategies for breeding high density-tolerant maize cultivars.