<i>Arabidopsis</i> TBP-ASSOCIATED FACTOR 12 ortholog NOBIRO6 controls root elongation with unfolded protein response cofactor activity.

Abstract

Plant root growth is indeterminate but continuously responds to environmental changes. We previously reported on the severe root growth defect of a double mutant in <i>bZIP17</i> and <i>bZIP28</i> (<i>bz1728</i>) modulating the unfolded protein response (UPR). To elucidate the mechanism by which <i>bz1728</i> seedlings develop a short root, we obtained a series of <i>bz1728</i> suppressor mutants, called <i>nobiro</i>, for rescued root growth. We focused here on <i>nobiro6</i>, which is defective in the general transcription factor component TBP-ASSOCIATED FACTOR 12b (TAF12b). The expression of hundreds of genes, including the bZIP60-UPR regulon, was induced in the <i>bz1728</i> mutant, but these inductions were markedly attenuated in the <i>bz1728nobiro6</i> mutant. In view of this, we assigned transcriptional cofactor activity via physical interaction with bZIP60 to NOBIRO6/TAF12b. The single <i>nobiro6</i>/<i>taf12b</i> mutant also showed an altered sensitivity to endoplasmic reticulum stress for both UPR and root growth responses, demonstrating that NOBIRO6/TAF12b contributes to environment-responsive root growth control through UPR.