The main research objective was to unravel the importance of the endoplasmic reticulum (ER) for genomic auxin responses. The PIN-LIKES (PILS) putative carriers for auxinic compounds localize to the ER, where they determine the cellular sensitivity to auxin (Barbez et al., 2012). I furthermore proposed to use the apical hook development as a model for differential growth control in plants. The apical hook is a dark grown, protective structure, showing asymmetric repression (during the formation) and promotion of growth (during opening). Using this system, we could reveal a role of PILS-dependent reduction in auxin signalling for growth induction in apical hooks (Beziat et al., 2017). We assume that PILS proteins transport auxin into the ER, thereby reducing auxin diffusion into the nucleus. In agreement, PILS proteins do reduce the abundance of nuclear auxin (Feraru et al., 2018 preprint). This work reveals that PILS proteins do not only affect auxin homeostasis (Barbez et al., 2012), but have a developmental role in controlling growth by depleting nuclear abundance (Feraru et al., 2018 preprint) and consequently signalling of auxin (Beziat et al., 2017; Feraru et al., 2018 preprint). Intriguingly, PILS proteins are utilized to integrate environmental stimuli, such as light (Beziat et al., 2017) and temperature (Feraru et al., 2018 preprint), into auxin-dependent growth programs. On the other hand, we revealed that also internal signals, such as other hormones, impact on PILS transcription (Sun et al., manuscript in preparation), suggesting that PILS proteins at the ER are important integrators of internal and external signals, modulating genomic auxin responses.
