Light and temperature-dependent developmental role of Auxin Binding Protein 1 (ABP1) in Arabidopsis thaliana

Auxin Binding Protein 1 (ABP1) is a small glycoprotein of about 22 kDa that has long been debated as the auxin receptor, and has been put into question for its unclear functions. Despite its conservancy during land plant evolution, its precise role in plant development is still elusive. Historically, it has been implicated in various rapid responses such as membrane polarization, calcium fluxes, TMK1-based cell-surface signalling, auxin canalization, etc. A relatively recent observation questioning the role of ABP1 in plant development led us to explore its probable functions if any. In the current study, we reinvestigated the plausible function of ABP1 using its CRISPR-based loss-of-function mutants, namely abp1-C1 and abp1-C2. Here we show that, ABP1 acts as a positive regulator for primary root elongation under red and secondary root elongation under blue light in seedlings at 22 {degrees}C. Under red light at 18 {degrees}C, it has a negative effect on hypocotyl growth inhibition. Furthermore, it is involved in flowering time control at 18 {degrees}C irrespective of the photoperiod. We show that the transcript levels of Phytochrome B (phyB) and GIGANTEA (GI) are altered in the mutants of ABP1 under red light and low temperature (18 {degrees}C) regimes. Further, ABP1 show a pronounced role in tolerance to dehydration induced due to low temperature (18 {degrees}C), which correlates with an increase in endogenous abscisic acid (ABA), salicylic acid (SA), and a decrease in jasmonic acid (JA) content in leaves. The functional roles of ABP1 under red light, low temperature and dehydration tolerance in Arabidopsis thaliana once again frames it to be an important regulator under adverse and varied conditions that the plant can experience, and thus opened up new avenues for further studies.