Timing of development - The role of SRR1 at the intersection between circadian timekeeping and flowering time control

• Applicant: Mikael Johansson, Ph.D.
• Subject Area: Plant Physiology
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 280344460

During their life cycle, plants progress through three distinct developmental stages. In the initial juvenile phase, the plant has not yet acquired the ability to respond to flowering-promoting environmental signals. In the following adult vegetative phase the plant has acquired flowering competence but is focused on acquiring biomass until environmental conditions are suitable for reproduction. In the final reproductive phase, the plant reallocates its resources to produce flowers and offspring. The transition between these phases needs to be carefully timed to ensure reproductive success. A major environmental signal influencing these transitions is the daylength, measured by the circadian clock. This endogenous, biological timekeeper stimulates flowering in long spring and summer days, by promoting the expression of the floral integrator gene FLOWERING LOCUS T (FT), considered to be part of the long sought florigen.SENSITIVITY TO RED LIGHT REDUCED 1 (SRR1) is a pioneer protein that is important for correct pacing of the circadian clock and for flowering time control. We have recently established that SRR1 acts as a repressor of flowering in noninductive short days, by promoting expression of several repressors of FT. This proposal aims at studying how SRR1 acts on the molecular level to regulate flowering time. As SRR1 is necessary for the correct pace of the clock, it is likely to interact with other clock proteins. Therefore, interaction studies between SRR1 and the proteins making up the evening complex of the circadian clock will be performed. To reveal additional genes that act in concert with SRR1 in flowering time control, a second site suppressor screen will be performed on an EMS-mutagenized population of srr1-1 mutants. Mutagenized plants will be screened for second site mutations that alleviate the prominent early flowering phenotype of srr1-1. These mutations will then be identified through a combination of linkage mapping and full genome sequencing. Preliminary data show that SRR1 associates with chromatin. Thus, a global profiling of SRR1 targets in the genome will be performed using ChIP-Seq. This will also reveal whether there are any common binding motifs necessary for SRR1 association of the DNA. The combination of these approaches will help me placing SRR1 into the flowering time network and explain how SRR1 acts on the molecular level to regulate important growth stage transitions in Arabidopsis.

• DFG Programme: Research Grants