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Plants deploy versatile scaffold proteins to intricately modulate complex cell signaling. Among these, RACK1A (Receptors for Activated C Kinase 1A) stands out as a multifaceted scaffold protein functioning as a central integrative hub for diverse signaling pathways. However, the precise mechanisms by which RACK1A orchestrates signal transduction to optimize seedling development remain largely unclear. Here, we demonstrate that RACK1A facilitates hypocotyl elongation by functioning as a flexible platform that connects multiple key components of light signaling pathways. RACK1A interacts with PHYTOCHROME INTERACTING FACTOR (PIF)3, enhances PIF3 binding to the promoter of BBX11 and down‐regulates its transcription. Furthermore, RACK1A associates with ELONGATED HYPOCOTYL 5 (HY5) to repress HY5 biochemical activity toward target genes, ultimately contributing to hypocotyl elongation. In darkness, RACK1A is targeted by CONSTITUTIVELY PHOTOMORPHOGENIC (COP)1 upon phosphorylation and subjected to COP1‐mediated degradation via the 26 S proteasome system. Our findings provide new insights into how plants utilize scaffold proteins to regulate hypocotyl elongation, ensuring proper skoto‐ and photo‐morphogenic development. [ABSTRACT FROM AUTHOR]

Summary: Brassinosteroids (BRs) are a group of plant‐specific steroid hormones, which induces the rapid nuclear localization of the positive transcriptional factors BRASSINAZOLE RESISTANT1/2 (BZR1/2). However, the mechanisms underlying the regulation of nucleocytoplasmic shuttling of BZR1 remain to be fully elucidated.In this study, we show that the scaffold protein Receptor for Activated C Kinase 1 (RACK1) from Arabidopsis is involved in BR signaling cascades through mediating the nuclear localization of BZR1, which is tightly retained in the cytosol by the conserved scaffold protein 14‐3‐3s.RACK1 can interact with BZR1 and competitively decrease the 14‐3‐3 interaction with BZR1 in cytosol, which efficiently enhances the nuclear localization of BZR1. 14‐3‐3 also retains RACK1 in cytosol through their interaction. Conversely, BR treatment enhances the nuclear localization of BZR1 by disrupting the 14‐3‐3 interaction with RACK1 and BZR1.Our study uncovers a new mechanism that integrates two kinds of conserved scaffold proteins (RACK1 and 14‐3‐3) coordinating BR signaling event. [ABSTRACT FROM AUTHOR]

Plants have adopted versatile scaffold proteins to facilitate the crosstalk between multiple signaling pathways. Leaf senescence is a well‐programmed developmental stage that is coordinated by various external and internal signals. However, the functions of plant scaffold proteins in response to senescence signals are not well understood. Here, we report that the scaffold protein RACK1A (RECEPTOR FOR ACTIVATED C KINASE 1A) participates in leaf senescence mediated by ethylene signaling via the coordination of the EIN3‐miR164‐ORE1 transcriptional regulatory cascade. RACK1A is a novel positive regulator of ethylene‐mediated leaf senescence. The rack1a mutant exhibits delayed leaf senescence, while transgenic lines overexpressing RACK1A display early leaf senescence. Moreover, RACK1A promotes EIN3 (ETHYLENE INSENSITIVE 3) protein accumulation, and directly interacts with EIN3 to enhance its DNA‐binding activity. Together, they then associate with the miR164 promoter to inhibit its transcription, leading to the release of the inhibition on downstream ORE1 (ORESARA 1) transcription and the promotion of leaf senescence. This study reveals a mechanistic framework by which RACK1A promotes leaf senescence via the EIN3‐miR164‐ORE1 transcriptional cascade, and provides a paradigm for how scaffold proteins finely tune phytohormone signaling to control plant development. [ABSTRACT FROM AUTHOR]

Maintenance of root growth is essential for plant adaptation to soil drying. Here, we tested the hypothesis that auxin transport is involved in mediating ABA's modulation by activating proton secretion in the root tip to maintain root growth under moderate water stress., Rice and Arabidopsis plants were raised under a hydroponic system and subjected to moderate water stress (−0.47 MPa) with polyethylene glycol ( PEG). ABA accumulation, auxin transport and plasma membrane H+- ATPase activity at the root tip were monitored in addition to the primary root elongation and root hair density., We found that moderate water stress increases ABA accumulation and auxin transport in the root apex. Additionally, ABA modulation is involved in the regulation of auxin transport in the root tip. The transported auxin activates the plasma membrane H+- ATPase to release more protons along the root tip in its adaption to moderate water stress. The proton secretion in the root tip is essential in maintaining or promoting primary root elongation and root hair development under moderate water stress., These results suggest that ABA accumulation modulates auxin transport in the root tip, which enhances proton secretion for maintaining root growth under moderate water stress. [ABSTRACT FROM AUTHOR]

ABSTRACT 14-3-3 proteins are a large family of proteins but exact roles of their members in plant response to abiotic stresses are not clear, especially under nutrient deficiency. We investigated the expressions of all the tomato 14-3-3 gene family members ( TFT1- TFT12) under low phosphorus stress (LP) and found that TFT6 belongs to the later responsive gene while TFT7 belongs to the early responsive gene. When the two genes were separately introduced into Arabidopsis and overexpressed, their plant growth under LP was much enhanced compared with wild-type plant. TFT6 overexpressing plants showed reduced starch synthase activity, reduced starch content but enhanced sucrose loading into phloem in the shoot under LP. TFT7 overexpressing plants had much enhanced H+ flux along their root tip and activity of plasma membrane H+-ATPase in the roots under LP. Our results suggest that TFT6 and TFT7 play different roles in plant adaption to LP. TFT6 acts mainly in leaves and is involved in the systemic response to LP by regulating leaf carbon allocation and increasing phloem sucrose transport to promote root growth, while TFT7 directly functions in root by activating root plasma membrane H+-ATPase to release more protons under LP. [ABSTRACT FROM AUTHOR]

Summary Light and brassinosteroids (BR) are indispensable for plant growth and control cell division in the apical meristem. However, how external light signals cooperate with internal brassinosteroids to program root meristem development remains elusive. We reveal that the photoreceptor phytochrome B (phyB) guides the scaffold protein RACK1 to coordinate BR signaling for maintaining root meristematic activity. phyB and RACK1 promote early root meristem development. Mechanistically, RACK1 could reinforce the phyB–SPA1 association by interacting with both phyB and SPA1, which indirectly affects COP1‐dependent RACK1 degradation, resulting in the accumulation of RACK1 in roots. Subsequently, RACK1 interacts with BES1 to repress its DNA‐binding activity toward the target gene CYCD3;1, leading to the release of BES1‐mediated inhibition of CYCD3;1 transcription, and hence the promotion of root meristem development. Our study provides mechanistic insights into the regulation of root meristem development by combination of light and phytohormones signals through the photoreceptors and scaffold proteins. [ABSTRACT FROM AUTHOR]