Type-B ARR Transcription Factors, ARR10 and ARR12, are Implicated in Cytokinin-Mediated Regulation of Protoxylem Differentiation in Roots of Arabidopsis thaliana

Abstract

In the phosphorelay-mediated cytokinin signal transduction of Arabidopsis thaliana, certain members of the type-B authentic response regulator (ARR) family are implicated in the regulatory networks that are primarily propagated by the cytokinin-receptors [authentic histidine kinases (AHKs)]. Clarification of the involvement of each type-B ARR transcription factor in cytokinin-responsive phenomena is still at a very early stage. Here we analyzed the redundant function of two type-B ARR genes, ARR10 and ARR12, by constructing an arr10/arr12 double mutant. The resulting mutant plants showed stronger phenotypes with special reference to the cytokinin action in roots (e.g. inhibition of root elongation, green callus formation from root explants) than those for each single mutant, suggesting that ARR10 and ARR12 redundantly play an important role in the cytokinin signaling in roots. This idea was further supported by results from root-specific microarray analyses with the double mutant plant. We also showed that ARR10 and ARR12 are involved in the AHK-dependent signaling pathway that negatively regulates protoxylem specification in root vascular tissues. When the double mutant is combined with an arr1 allele, the resultant arr1/arr10/arr12 triple mutant showed phenotypes displaying a very poor growth, quite similar to those of the wooden leg (wol) mutant that virtually lacks cytokinin receptor activities in plants. In this triple arr mutant, the specification of root vascular tissues is also affected as severely as in wol. Taken together, we propose that ARR10 and ARR12, together with ARR1, redundantly play pivotal roles in the AHK-dependent phosphorelay signaling in response to cytokinin in roots.

STIMPY mediates cytokinin signaling during shoot meristem establishment in Arabidopsis seedlings

“…We also found similar reductions in STIP mRNA levels in the roots of the type-B arr1-3 arr10-5 arr12-1 triple-mutant seedlings (Fig. 1H), which are nearly completely insensitive to cytokinin stimulation in the roots (Argyros et al, 2008;Yokoyama et al, 2007). Although we cannot rule out the possibility that the observed reductions in STIP expression are caused by morphological changes due to the lack of cytokinin signaling, these findings are consistent with our hypothesis that STIP acts downstream of the cytokinin signaling pathways.…”

Two-Component Signaling Elements and Histidyl-Aspartyl Phosphorelays†

“…in the cytokinin signaling pathway (Rashotte et al, 2006;Yokoyama et al, 2007). A number of primary response genes directly regulated by the type-B ARRs have been identified, including the type-A ARRs (Taniguchi et al, 2007).…”

A Link between Cytokinin andASL9(ASYMMETRIC LEAVES 2 LIKE 9) That Belongs to theAS2/LOB(LATERAL ORGAN BOUNDARIES) Family Genes inArabidopsis thaliana

“…Microarray analysis was performed using a GeneChip Ò ATH1 Arabidopsis genome array (Affymetrix, Santa Clara, CA), as described previously. 14) Note that triplicate results were obtained for each strain.…”