The presence of competing plants in the physical proximity is perceived in terms of reducing the proportion of red light (R, English network) and far-red (FR, far-red English), or ratio R: FR, the incident radiation. Anticipating shaded by other plants, the perception of low light ratio R: FR, conducted by the photoreceptor phytochrome, launches the so-called syndrome escape from the shadow “(SAS, its acronym in English), a stimulating set of responses, including the longitudinal growth at the expense of the accumulation of photoassimilates in harvestable organs, or bloom.


At the molecular level, the implementation of SAS induces rapid changes in gene expression. In this work, coordinated by Professor Martinez-Garcia, has addressed the role of PAR1 and PAR2 (Rapidly Phytochrome Regulated), two Arabidopsis genes whose expression is induced rapidly after the perception of plant proximity. These two genes encode proteins atypical family of transcription factors of the type bHLH (basic-helix-loop-helix). Using genetic strategies has shown that PAR1 and PAR2 in the nucleus act as negative regulators of SAS.


From a molecular standpoint, PAR1 and PAR2 act as direct transcriptional repressors of the expression of two auxin-responsive genes, and SAUR68 SAUR15 (Small Auxin upregulated). The absence of a conserved domain of DNA binding proteins in PAR1 and PAR2 implies that they regulate gene expression not directly but by modulating the DNA binding of transcription factors to interact through the HLH domain, acting as transcriptional cofactors.
Taken together, these results led to propose that these small atypical bHLH proteins would connect quickly the perception of the shadow by phytochromes and sensitivity to hormones, integrating the relevant transcriptional networks in plants.