OsbZIP48, a HY5 Transcription Factor Ortholog, Exerts Pleiotropic Effects in Light-Regulated Development

Abstract

Plants have evolved an intricate network of sensory photoreceptors and signaling components to regulate their development. Among the light signaling components identified to date, HY5, a basic leucine zipper (bZIP) transcription factor, has been investigated extensively. However, most of the work on HY5 has been carried out in Arabidopsis (Arabidopsis thaliana), a dicot. In this study, based on homology search and phylogenetic analysis, we identified three homologs of AtHY5 in monocots; however, AtHYH (HY5 homolog) homologs are absent in the monocots analyzed. Out of the three homologs identified in rice (Oryza sativa), we have functionally characterized OsbZIP48. OsbZIP48 was able to complement the Athy5 mutant. OsbZIP48 protein levels are developmentally regulated in rice. Moreover, the OsbZIP48 protein does not degrade in dark-grown rice and Athy5 seedlings complemented with OsbZIP48, which is in striking contrast to AtHY5. In comparison with AtHY5, which does not cause any change in hypocotyl length when overexpressed in Arabidopsis, the overexpression of full-length OsbZIP48 in rice transgenics reduced the plant height considerably. Microarray analysis revealed that OsKO2, which encodes ent-kaurene oxidase 2 of the gibberellin biosynthesis pathway, is down-regulated in OsbZIP48OE and up-regulated in OsbZIP48 KD transgenics as compared with the wild type. Electrophoretic mobility shift assay showed that OsbZIP48 binds directly to the OsKO2 promoter. The RNA interference lines and the T-DNA insertional mutant of OsbZIP48 showed seedling-lethal phenotypes despite the fact that roots were more proliferative during early stages of development in the T-DNA insertional mutant. These data provide credible evidence that OsbZIP48 performs more diverse functions in a monocot system like rice in comparison with its Arabidopsis ortholog, HY5.

OsbHLH073 Negatively Regulates Internode Elongation and Plant Height by Modulating GA Homeostasis in Rice

“…Rice NAC DOMAIN-CONTAINING PROTEIN 2 (OsNAC2) overexpression reduces plant height and internode length, and OsNAC2 represses the expression of OsKO2 by directly binding to its promoter, as shown in Chip-seq analysis and yeast one-hybrid analysis [65]. OsbZIP48 directly binds to the promoter of OsKO2 and regulates its expression to control internode elongation [66].…”

Uncovering candidate genes involved in photosynthetic capacity using unexplored genetic variation in Spring Wheat

“…Through the index NPQI we can also make inference about the level of chlorophyll degradation happening in the leaves 54 which can be indicative of plant senescence. We detected an association for NPQI in chromosome 7AL that contains HY5, an antagonist of PIF that controls the accumulation of chlorophyll in the leaves in response to phytochrome photoreceptor signalling 55 , which also causes delayed senescence in rice transgenic plants 56 . We also observed an association on 3BL for plant senescence itself through calculation of PSRI, this interval contains AHK2 a cytokinin receptor which controls leaf longevity in Arabidopsis and knockouts demonstrate a delayed senescence phenotype.…”

Coordination of light, circadian clock with temperature: The potential mechanisms regulating chilling tolerance in rice

“…Relevant to light signaling in rice, Nakamura et al (2007) identified a set of highly homologous rice proteins (designated OsPIL11 to OsPIL16) to be functional counterparts of PIF‐like proteins in Arabidopsis. Moreover, OsbZIP48 has been functionally characterized as an HY5 ortholog in rice, although it performs more diverse functions than its Arabidopsis ortholog and exerts pleiotropic effects in light‐regulated development (Burman et al 2018). OsCOP1, which directly interacts with OsCRY1, and is implicated in blue‐light inhibition of coleoptiles as well as in leaf elongation during early seedling development (Zhang et al 2006).…”