Abstract
ELONGATED HYPOCOTYL5 (HY5), a bZIP-type transcription factor, acts as a master regulator that regulates various physiological and biological processes in plants such as photomorphogenesis, root growth, flavonoid biosynthesis and accumulation, nutrient acquisition, and response to abiotic stresses. HY5 is evolutionally conserved in function among various plant species. HY5 acts as a master regulator of light-mediated transcriptional regulatory hub that directly or indirectly controls the transcription of approximately one-third of genes at the whole genome level. The transcription, protein abundance, and activity of HY5 are tightly modulated by a variety of factors through distinct regulatory mechanisms. This review primarily summarizes recent advances on HY5-mediated molecular and physiological processes and regulatory mechanisms on HY5 in the model plant Arabidopsis as well as in crops.
Highlights
Plants utilize light as the predominant energy source for photosynthesis
Extensive genetic and biochemical studies have established that the ELONGATED HYPOCOTYL5 (HY5), a bZIP-type transcription factor, tightly controls the light-regulated transcriptional alternation
HY5 to activate its transcription, while HY5 positively regulates the expression of BBX11, BBX21, and itself, forming a transcriptional feedback loop in controlling downstream target gene expression (Xu D. et al, 2016, 2018; Zhao et al, 2020; Job and Datta, 2021; Song et al, 2021). These findings suggest that a subgroup of B-box proteins (BBXs) and HY5 forms a complex transcriptional network that orchestrates the expression of light-responsive genes
Summary
Plants utilize light as the predominant energy source for photosynthesis. Besides, light signal acts as an essential external factor that mediates a variety of physiological and developmental processes in plants (Paik and Huq, 2019; Song et al, 2020a; Xu, 2020). MYC2, MYC3, and MYC5 bind to E-box cis-element present in the HY5 promoter to activate its expression, while HY5 inhibits the expression of MYC2, suggesting that MYCs and HY5 likely form a negative feedback loop in the regulation of seedling development (Chakraborty et al, 2019; Yi et al, 2020) These results indicate that plants acquired a complicated but delicate regulatory mechanism to fine-tune the HY5 transcript level and activity in the control of photomorphogenesis. Shoot SIHY5 moves to the root to promote phosphate uptake under phosphate starvation conditions (Ge et al, 2021) These results suggest that HY5 is necessary and required for precisely controlling multiple nutrient uptake and utilization in diverse plant species in response to fluctuating light signals (Figure 4). High temperatures tightly control the mode of HY5 action that contributes to both shoot and root thermosensory growth in plants
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