Plant cells are totipotent, and under ex vivo conditions, plant somatic cells can continuously regenerate through the acquisition of stem cell function, stem cell niche reconstruction, and growth point formation. Plant regeneration requires not only precise regulation of complex internal genetic networks, but also influences of the external environment (light, temperature, etc.). Light is one of the most important environmental factors, and it has been found that light is involved in regulating plant regeneration, but how light regulates plant regeneration is unclear.
Recently, Professor Xiang Fengning's team from the School of Life Sciences of Shandong University has made an important breakthrough in the regulation mechanism of plant regeneration. The results of the study, "HY5 inhibits in vitro shoot stem cell niches initiation via directly repressing pluripotency and cytokinin pathways," were published in The Plant Journal, a prestigious journal of botany.
The study found that low light intensity promotes ex vivo seedling regeneration, while high light intensity inhibits ex vitro seedling regeneration. Compared with dark conditions, different lights (red, far red, blue and white) promote the regeneration of ex vivo seedlings to varying degrees. Identification of the regenerative capacity of ex vivo seedlings under different light conditions by multiple optical transduction pathway-related mutants found that CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) is the main promoter of ex vivo seedling regeneration, whether in dark or under different lights (red, far red, blue and white), and ELONGATED HYPOCOTYL 5 (HY5) is the inhibitor of this process HY5 can inhibit ex vitro seedling regeneration by relying on light and not relying on light. Fluorescent signal observation found that the co-localization expression of the key genes WUS and CLV3 in STEM cells during SIM culture for 4 to 5 days was a marker of the initiation of the ex vivo stem cell center, and hy5 deletion promoted the co-localization expression of the two in the initiation and formation of the stem cell center. Molecular and biochemical experiments have found that HY5 can inhibit its expression by directly binding to the promoter of WUS and CLV3, and can also indirectly inhibit the expression of WUS and CLV3 by directly inhibiting the expression of cytokinin-responsive factor ARR12, thus demonstrating that HY5 achieves precise regulation of ex vivo seedling regeneration by dual regulation of WUS and CLV3 at the transcriptional level.
Fig 1. (a-g) HY5 inhibits shoot regeneration from root explants while COP1 promotes it under different light conditions. (h-i) Predicted temporal and spatial expression of CLV3 and WUS in root explants exposed to continuous white light.
Fig 2. A working model to demonstrate how HY5 could inhibit shoot regeneration from explants cultured in the presence of light and in the dark.
In summary, the study proves that HY5 is a key factor in mediating the regulation of ex vivo seedling regeneration by light signaling, reveals that HY5 is the hub of molecular regulation network connecting optical signaling, stem cell signaling and cytokinin signaling, discovers a new pathway for COP1-HY5 to regulate the regeneration of ex vivo seedlings, and initially elucidates the potential mechanism of optical signal regulation of ex vivo seedling regeneration.
Xiang Fengning's research group has long been engaged in the molecular mechanism of Arabidopsis thaliana ex vitro seedling regeneration, using the ex vivo culture system, identifying a number of important functional genes and miRNAs involved in ex vitro seedling regeneration, and analyzing their molecular pathways to control ex vitro seedling regeneration, the related research results were published in The Plant Cell 2020; The Plant Journal 2021; 2016a;2016b;2012;J Integr Plant Biol. 2021; 2017 and other journals. The research results proved the influence of the external environment-light on plant regeneration, and revealed the regulatory mechanism of HY5-mediated light signal on the regeneration of ex vivo seedlings. These research achievements not only provide important clues for the analysis of the major scientific problem in the field of botany "plant cell totipotency mechanism", but also provide theoretical guidance for promoting the application of plant ex vivo rapid propagation and crop gene editing technology.
The paper is based on Shandong University as the first and corresponding author unit, postdoctoral Dai Xuehuan (now lecturer of the College of Agronomy of Qingdao Agricultural University) as the first author, and Professor Xiang Fengning as the corresponding author. The research has been funded by the National Major Scientific Research Program, the National Key Research and Development Program, the National Natural Science Foundation of China and the Major Basic Research Of Shandong Province.
Full text links:
https://doi.org/10.1111/tpj.15703
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