SACL, a bHLH gene that restricts vascular cell proliferation in plants.

The final size and arrangement of the plant vasculature requires precise adjustment of cell proliferation. In particular, radial growth of vascular bundles is to a large extent controlled by a bHLH transcription factor heterodimer formed by TARGET OF MONOPTEROS5 (TMO5) and LONESOME HIGHWAY (LHW). Excess activity of this TMO5/LHW dimer causes excessive proliferation of vascular cell divisions and thus suggests the existence of a molecular mechanism that restricts its activity in space and time. Here we show that this overproliferation phenotype is similar to acaulis5 (acl5) mutants, suggesting a role for ACL5 in controlling TMO5/LHW activity. We further identify the clade of SAC51-LIKE (SACL) bHLH transcription factors whose translation is regulated by ACL5, as inhibitors of TMO5/LHW activity. We show that SACL proteins interact with LHW impairing activation of downstream targets and alleviating the overproliferation caused by TMO5/LHW misexpression. Given that transcription of SACL genes is induced by TMO5/LHW and its upstream trigger auxin, we propose that SACL proteins represent a feedback mechanism that limits activity of this pathway and controls periclinal cell divisions. Three biological replicates were generated per sample. The goal of this experiment is to compare different genotypes that suppress the acl5 mutant as Columbia-0, acl5 + pHS::SACL3 and acl5 ajax2-31, against the acl5 mutant. Every pair of samples that were compared in the same array, were also growth in the same plate. The acl5 + pHS::SACL3 seedlings (and the acl5 ones against they are went compared) were treated to 37C degrees heat shock and then collected at the different times (30 and 210 min) after heat shock. In each comparison 1 or 2 or the replcates were reversed-labeled.