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Phone: (612) 625-1234
Fax: (612) 625-1738

Department of Plant Biology
University of Minnesota
250 Biological Science Center
1445 Gortner Ave.
St. Paul, MN 55108

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Min Ni

Associate Professor, Department of Plant Biology
Ph.D., University of Oklahoma, 1992

Light signal transduction and photomorphogenesis

Contact Information

Mailing Address:

Dr. Min Ni
Department of Plant Biology
University of Minnesota
250 Biological Sciences Center
1445 Gortner Avenue
St. Paul, MN 55108

Office: 644 Biological Sciences Center
Phone: 612-625-3702
Fax: 612-625-1738
E-mail: nixxx008@umn.edu
Web Site: Min Ni Lab

Research Interests

Plants sense their ambient light conditions through a series of photoreceptors. The red/far-red light-absorbing phytochromes and UV-A/blue light-absorbing crytochromes regulate seedling de-etiolation, photoperiodic flowering, and circadian rhythm. The de-etiolation responses include the inhibition of hypocotyl elongation, the opening of cotyledons and hypocotyl hooks, and the development of chloroplasts. To understand the signaling events downstream of the photoperception, we have identified several mutants that have defective seedling de-etiolation responses under multiple wavelengths.

The first mutant family includes recessive hrb (hypersensitive to red and blue) mutants that were initially isolated for their short hypocotyl phenotype under red and blue light. We have cloned HRB1 and mapped hrb2 and hrb3 to chromosome 2 and chromosome 4, respectively. HRB1 encodes a nuclear protein that contains a ZZ-type zinc finger domain implicated in protein-protein interactions in other organisms. HRB1 activity is also required for red and blue light-induced expression of PIF4. Like hrb1, pif4 is hypersensitive to both red and blue light and pif4 is epistatic to hrb1. Thus, HRB1 and PIF4 may define points where red light signaling and blue light signaling intersect. In addition to its de-etiolation phenotypes, hrb1 also flowers late and attenuates the expression of FT, an integrator of several flowering induction pathways, under both long days and short days. In contrast, transgenic plants that overexpress full-length HRB1 or its C-terminal half flower early and accumulate more FT mRNA under short days. hrb1 is epistatic to cry2 in long-day flowering and FT expression, whereas phyB is epistatic to hrb1 in both long-day and short-day flowering and FT expression. HRB1 thus may act downstream of cry2 but modulates phyB signaling for photoperiodic flowering.

Another knockout mutant is short hypocotyl under blue 1 or shb1. However, shb1-D, a dominant gain-of-function allele due to the over-accumulation of SHB1 transcript, exhibited a long hypocotyl phenotype under red, far-red, and blue light. Therefore, SHB1 acts in blue light signaling and overexpression of SHB1 may expand its signaling activity to red and far-red light. Consistent with this, overexpression of SHB1 enhances expression of PIF4 under red light. PIF4 appears to specifically mediate SHB1 regulation of hypocotyl elongation and CAB3 or CHS expression under red light. Overexpression of SHB1 also promotes proteasome-mediated degradation of phyA and hypocotyl elongation under far-red light. Under blue light, shb1 suppresses HFR1 expression and shows several de-etiolation phenotypes similar to hfr1-201. However, the hypocotyl and cotyledon-opening phenotypes of shb1 are opposite to those of hfr1-201, and HFR1 acts downstream of SHB1. SHB1encodes a nuclear and cytosolic protein that contains SPX and EXS domains homologous to the SYG1 protein family. The function of the two domains and their interactions with other proteins remain largely unknown. We demonstrated that overexpression of the N-terminal 520 amino acids, harboring the intact SPX domain, caused a hyposensitive hypocotyl phenotype similar to that of shb1-D. In contrast, overexpression of several C-terminal truncations, all including the intact EXS domain, created a dominant-negative hypersensitive hypocotyl phenotype similar to that of shb1. To study how SHB1interacts with other genes, we have isolated a series of suppressors and enhancers of shb1-D that carry mutations either in the SHB1 gene or in different genetic loci. Since the genetic suppressors and enhancers may define proteins that directly interact with SHB1, we have conducted a preliminary screen of a yeast two-hybrid library for SHB1 interacting proteins.

Selected Publications

Kang, X., Zhou, Y., Sun, X., and Ni, M. (2007). HYPERSENSITIVE TO RED AND BLUE 1 and its C-terminal regulatory function define a signaling step that controls FLOWERING LOCUS T expression. Plant Journal (in press).

Zhou, Y., Sun, X., and Ni, M. (2007). Timing of photoperiodic flowering: light perception and circadian clock. J Integr Plant Biol 49, 28-34.

Chen, M., and Ni, M. (2006). RED AND FAR-RED INSENSITIVE 2, a RING-domain zinc-finger protein, negatively regulates CONSTANS expression and photoperiodic flowering. Plant Journal 46, 823-833.

Kang, X., and Ni, M. (2006). Arabidopsis SHORT HYPOCOTYL UNDER BLUE 1 contains SPX and EXS domains and acts in cryptochrome signaling. Plant Cell 18, 921-934.

Chen, M., and Ni, M. (2006). RED AND FAR-RED INSENSITIVE 2, a RING-domain zinc-finger protein, mediates phytochrome-controlled seedling de-etiolation responses. Plant Physiology 140, 457-465.

Ni, M. (2005). Integration of light signaling with photoperiodic flowering and circadian regulation. Cell Research 15, 559-566.

Ni, M. (2005). Downstream integrators of red, far-red, and blue light signaling for photomorphogenesis. In Light Sensing in Plants , M. Wada, K. Shimazaki, and M. Iino eds. ( Sringer-Verlag, Tokyo), 293-298.

Kang, X., Chong, J., and Ni, M. (2005). HYPERSENSITIVE TO RED AND BLUE 1, a ZZ-type zinc finger protein, regulates phytochrome B-mediated red and cryptochrome-mediated blue light responses. Plant Cell 17, 822-835.

Ni, M., Tepperman, J., and Quail, P.H. (1999). Binding of phytochrome B to its nuclear signaling partner PIF3 is reversibly induced by light. Nature 400, 781-784.

Halliday, K., Hudson, M., Ni, M., Qin, M., and Quail, P.H. (1999). poc1: an Arabidopsis mutant perturbed in phytochrome signaling due to a T-DNA insertion in the promoter of PIF3, a gene encoding a phytochrome-interacting, bHLH protein. PNAS 96, 5832-5837.

Ni, M., Tepperman, J., and Quail, P.H. (1998). PIF3, a phytochrome interacting factor necessary for photoinduced signal transduction, is a basic helix-loop-helix protein. Cell 95, 657-667.

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