Abstract  (Prof Hongquan Yang) - Cryptochromes (CRYs) are blue light photoreceptors that mediate a variety of light responses in plants, including photomorphogenesis, flowering, and circadian rhythms. The signaling mechanism by which Arabidopsis thaliana cryptochromes CRY1 and CRY2 promote photomorphogenesis involves direct interactions with COP1, a RING motif-containing E3 ubiquitin ligase, and its enhancer SPA1. Auxin and brassinosteroid (BR) are key phytohormones involved in the repression of photomorphogenesis. The molecular mechanisms underlying the antagonistic interactions of light with auxin and BR signaling remain unclear. We show that light inhibits auxin signaling through stabilization of AUX/IAA proteins (AUX/IAAs) by blue light-dependent interactions of CRY1 with AUX/IAAs. Blue light-triggered interactions of CRY1 with AUX/IAAs inhibit the associations of the auxin receptor TIR1 with AUX/IAAs, leading to the repression of auxin-induced degradation of these proteins. Our results indicate that photoreceptor shares AUX/IAAs with the auxin receptor as the same direct downstream signaling components. We propose that antagonistic regulation of AUX/IAA protein stability by photoreceptor and auxin receptor allows plants to balance light and auxin signals to optimize their growth. Moreover, we show that CRY1 interacts directly with Auxin Response Factors 6 and 8 (ARF6/8) in a blue light-dependent manner, to repress their DNA-binding activity and target genes expression, to inhibit auxin signaling. We also show that CRY1 and CRY2 physically interact with BES1-INTERACTING MYC-LIKE1 (BIM1), a basic helix-loop-helix protein that in turn interacts with and enhances the activity of BRI1-EMS SUPPRESSOR1 (BES1), a master transcription factor in the BR signaling pathway. In addition, CRY1 and CRY2 interact specifically with dephosphorylated BES1, the physiologically active form of BES1 that is activated by BR in a blue light-dependent manner. The CRY1-BES1 interaction leads to both the inhibition of BES1 DNA binding activity and the repression of its target gene expression. Our study suggests that the blue light-dependent, BR-induced interaction of CRY1 with BES1 is a tightly regulated mechanism by which plants optimize photomorphogenesis according to the availability of external light and internal BR signals.

Abstract (Prof Zhongnan Yang) - Sporopollenin is the major outer wall component of pollen and spores. Aliphatic units were reported to be essential components of sporopollenin. Multiple genes associated with the modification of aliphatic units for sporopollenin synthesis have been identified. In Arabidopsis, we demonstrate a genetic pathway that directly regulates the expression of these genes. Sporopollenin is one of the critical innovations for plant landing and dispersal in terrestrial environment as it can protect male gametophytes (pollen and spore) from UV damage. Intermediates from phenylpropanoid metabolism can flow to formation of lignin, flavonoids, and hydroxycinnamoyl esters. We found the phenylpropanoid metabolites (monolignol and hydroxycinnamates) are also essential components of sporopollenin. They provide protection for genome of the male gametophytes from UV damage. Different phenylpropanoid derivatives were detected in sporopollenin of pteridophytes and seed plants. The integration of different phenylpropanoid derivatives into sporopollenin reflects an evolution course after plant landing.

Biography of each Professor

Prof Hongquan Yang
Quan, Ph.D., Professor of Biology, Yangtze River Scholar, Chinese
National Science Fund for Distinguished Young Scholars
Email: hqyang@shnu.edu.cn

2018.07 - present, Professor, Shanghai Normal University
2015 - 2018, Professor, Fudan University
2006 - 2015, Professor, Shanghai Jiaotong University
2001 - 2006, Professor, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences
2000 - 2001, Research Associate, Department of Biology, University of Pennsylvania
1995 - 2000, Postdoctoral Associate, Department of Biology, University of Pennsylvania
1995, Ph.D., Shanghai Institute of Plant Physiology, Chinese Academy of Sciences

Prof Zhongnan Yang

Ph.D., Professor of Biology, Chinese National Science Fund for Distinguished Young Scholars (2009)
E-mail: znyang@shnu.edu.cn
2002 - present, Professor, Shanghai Normal University
1995 - 2001, Postdoctoral Research Associate, Texas A&M University
1993 - 1994, Research Associate, Shanghai Institute of Plant Physiology(SIPP), Chinese Academy of Sciences (CAS)
1987 - 1993, Ph.D., SIPP, CAS