Type B Response Regulators Act As Central Integrators in Transcriptional Control of the Auxin Biosynthesis Enzyme TAA1

Abstract

During embryogenesis and organ formation, establishing proper gradient is critical for auxin function, which is achieved through coordinated regulation of both auxin metabolism and transport. Expression of auxin biosynthetic genes is often tissue specific and is regulated by environmental signals. However, the underlying regulatory mechanisms remain elusive. Here, we investigated the transcriptional regulation of a key auxin biosynthetic gene, l-Tryptophan aminotransferase of Arabidopsis1 (). A canonical and a novel Arabidopsis () response regulator (ARR) binding site were identified in the promoter and the second intron of , which were required for its tissue-specific expression. C-termini of a subset of the type B ARRs selectively bind to one or both cis elements and activate the expression of We further demonstrated that the ARRs not only mediate the transcriptional regulation of by cytokinins, but also mediate its regulation by ethylene, light, and developmental signals. Through direct protein-protein interactions, the transcriptional activity of ARR1 is enhanced by ARR12, DELLAs, and ethylene-insenstive3 (EIN3). Our study thus revealed the ARR proteins act as key node that mediate the regulation of auxin biosynthesis by various hormonal, environmental, and developmental signals through transcriptional regulation of the key auxin biosynthesis gene.

WD40‐REPEAT 5a represses root meristem growth by suppressing auxin synthesis through changes of nitric oxide accumulation in Arabidopsis

“…Cytokinin also modulates root growth (Kushwah et al ., ; Raines et al ., ). A recent report indicated that type‐B response regulators in cytokinin signaling functions in root growth by binding to the TAA1 promoter to regulate its transcription (Yan et al ., ). Also, this phytohormone can promote NO accumulation to inhibit root growth (Shen et al ., ).…”

“…B response regulators in cytokinin signaling functions in root growth by binding to the TAA1 promoter to regulate its transcription (Yan et al, 2017). Also, this phytohormone can promote NO accumulation to inhibit root growth (Shen et al, 2013).…”

Root-derivedtrans-zeatin cytokinin protectsArabidopsisplants against photoperiod stress

“…An interaction of ARR2 and ARR14 has been described using a two-hybrid system in yeast (Dortay, Mehnert, Bürkle, Schmülling, & Heyl, 2006). Recently, it was found that the C-termini of ARR1 and ARR12 interact to regulate auxin synthesis (Yan et al, 2017). It could also be that interactions between type-B ARRs are context-dependent as it is known for the phosphorylation-dependent homodimerization of bacterial RRs (Mack, Gao, & Stock, 2009).…”

“…Beside the interaction amongst ARRs, interactions between several type-B ARRs and other proteins exist. For example, ARR1, ARR2 and ARR14 interact with the DELLA proteins RGA1 and GAI to regulate root development and photomorphogenesis (Marín-de la Rosa et al, 2015; Yan et al, 2017). During the regulation of auxin synthesis, EIN3 interacts with the C-terminus of ARR1 and thereby increases ARR1 activity (Yan et al, 2017).…”

“…For example, ARR1, ARR2 and ARR14 interact with the DELLA proteins RGA1 and GAI to regulate root development and photomorphogenesis (Marín-de la Rosa et al, 2015; Yan et al, 2017). During the regulation of auxin synthesis, EIN3 interacts with the C-terminus of ARR1 and thereby increases ARR1 activity (Yan et al, 2017). As part of the crosstalk between CK and abscisic acid, ARR1, ARR11 and ARR12 directly interact with SUCROSE NON-FERMENTING-1 (SNF1)- RELATED PROTEIN KINASE2 (SnRK2) kinases and thereby inhibit their function prior to drought stress (Huang et al, 2018).…”