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 Zm CRY1,we obtained two Zm CRY1a genes(Zm CRY1a1 and Zm CRY1a2),both of which share the highest similarity with other gramineous plants,in particular rice CRY1a by phylogenetic analysis.In Arabidopsis,overexpression of Zm CRY1a 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(Zm CRY1aOE),overexpression of Zm CRY1a 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 Zm CRY1a genes.Expression of Zm CRY1a 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 Zm CRY1a genes to LBL treatment.We confirmed a link between Zm CRY1a expression and hormonal influence on the growth and development of maize under LBL-induced SAS.These results reveal that Zm CRY1a has a relatively conservative function in regulating maize photomorphogenesis and may guide new strategies for breeding high density-tolerant maize cultivars.

Phenotypic analysis and molecular characterization of an allelic mutant of the D61 gene in rice

Brassinosteroids(BRs) are a class of plant-specific steroidal hormones that play important roles in multiple biological processes. In this paper, a classic rice mutant gsor300084,showing erect leaves and semi-dwarf stature, was characterized. Morphological analysis in darkness showed that the mesocotyl of the gsor300084 mutant did not elongate when grown in darkness. Coleoptile elongation and root growth were less affected by the exogenous application of brassinolide(BL), the most active form of BR, in gsor300084 than in the wild-type rice variety Matsumae. Lamina joint bending analysis also showed that gsor300084 was less sensitive to exogenous BL than Matsumae. These results suggested that the gsor300084 mutant is defective in BR sensitivity. Map-based cloning indicated that gsor300084 is a novel allelic mutant of the DWARF61(D61) gene, which encodes the putative BR receptor OsBRI1. A single-base mutation appears in the LRR domain of OsBRI1, changing the 444 th amino acid from tryptophan(W) to arginine(R). Subcellular localization analysis suggested that both the wild-type and mutant OsBRI1 protein are localized at the cytoplasmic membrane. Structure modeling revealed that the W444 R substitution may affect the perception of BRs by the LRR domain.