Component of TORC1 complex, which is an essential cell growth regulator that controls plant development. Acts by activating transcription, protein synthesis and ribosome biogenesis, and inhibiting mRNA degradation and autophagy (Probable). Involved in regulating amino acid accumulation and the synthesis of myo-inositol and raffinose during plant adaptation to long days (PubMed:22307851). Involved in the regulation of plant growth and abscisic acid (ABA) accumulation. Acts as positive regulation of the ABA biosynthetic genes ZEP, NCED3 and AAO3, and negative regulator of the ABA catabolic genes CYP707A2 and CYP707A3 (PubMed:26459592). The target of rapamycin complex 1 (TORC1) is composed of at least RAPTOR, LST8 and TOR (Probable). Interacts with TOR (PubMed:22307851). Expressed in the root central cylinder, root tips, emerging lateral roots, vasculature of cotyledons, leaf stomata, leaf stipules, anthers, pollen, filaments, and vasculature of petals and sepals. Reduced growth and unable to flower under short day conditions. Retarded growth, bushy rosettes, development of multiple apical meristems and unable to flower under long day conditions. Belongs to the WD repeat LST8 family.