General regulator required for the development of the entire plant. Regulates the duration of cell cycle (PubMed:20736351). Probable activator of Rab GTPases and upstream regulator of the cell growth-regulating TOR (target of rapamycin) network (PubMed:19060111, PubMed:20736351). Might also control spatial growth in pollen tubes or root hairs via the TORC2 signaling branch (PubMed:19060111). Involved in the regulation of abscisic acid- and calcium-mediated stomatal closure, but not in light or H(+)-pumping induced stomatal opening. May regulate microtubules depolymerization (PubMed:22610367). Binds calcium and has a cytoprotective function (PubMed:24040826). Homodimer. Interacts with the Rab GTPases RABA4A, RABA4B, RABF1 and RABF2B (PubMed:20736351). Interacts with microtubules and heterodimers of alpha- and beta-tubulins. Cytosolic calcium positively regulates this interaction (PubMed:22610367). Expressed in flowers, leaves and stems (PubMed:16902407, PubMed:19060111). Expressed in roots and siliques. Detected in seeds. Highest expression in actively dividing and differentiating cell types, such as the meristematic and division zones of the root, the embryo or the elongating tube of germinating pollen (PubMed:19060111). Expressed in cotyledons, leaves, hypocotyls and roots. Detected in mitotically active tissues such as shoot apical meristems, root tips, lateral root initiation regions and anthers, and in guard cells (PubMed:22610367). Up-regulated by momilactone B (PubMed:26058145). Not regulated by light (PubMed:19060111). Up-regulated by abscisic acid (PubMed:22610367). Male gametophytic phenotype with normal pollen formation and germination but impaired pollen tube growth (PubMed:19060111). Embryonic lethality when homozygous due to a retarded development of the embryos that eventually collapse at the silique dehiscence stage (PubMed:20736351). Knockdown mutants have retarded growth due to decreased cell size. Belongs to the TCTP family.