The receptor-like kinase SIT1 acts as a sensor in rice (Oryza sativa) roots, relaying salt stress signals via elevated kinase activity to enhance salt sensitivity. Here, we demonstrate that Protein Phosphatase 2A (PP2A) regulatory subunit B'kappa constrains SIT1 activity under salt stress. B'kappa-PP2A deactivates SIT1 directly by dephosphorylating the kinase at Thr515/516, a salt-induced phosphorylation site in the activation loop that is essential for SIT1 activity. B'kappa overexpression suppresses the salt sensitivity of rice plants expressing high levels of SIT1, thereby contributing to salt tolerance. B'kappa functions in a SIT1 kinase-dependent manner. During early salt stress, activated SIT1 phosphorylates B'kappa; this not only enhances its binding with SIT1, it also promotes B'kappa protein accumulation via Ser502 phosphorylation. Consequently, by blocking SIT1 phosphorylation, B'kappa inhibits and fine-tunes SIT1 activity to balance plant growth and stress adaptation.

The American biologist Winslow Russel Briggs (1928-2019) was a global leader in plant physiology, genetics and photobiology. In this contribution, we try to share our knowledge of the remarkable career of this outstanding scientist. After earning his PhD at Harvard (Cambridge, Massachusetts), he started his independent research program at Stanford University (California). Among many major contributions was his elegant experiment that conclusively demonstrated the role of auxin transport in the phototropic bending response of grass coleoptiles. During subsequent years as Professor of biology at Harvard University, Briggs focused on phytochrome and photomorphogenesis. In 1973, he re-located to Stanford to become Director of the Department of Plant Biology, Carnegie Institution for Science, and faculty member in the Biology Department at Stanford University. After his retirement (1993), he continued his research on "light and plant development" as an emeritus at Carnegie until the day of his death on February 11, 2019. Through his long research career, Briggs stayed at the cutting edge by re-inventing himself from a plant physiologist, to biochemist, geneticist, and molecular biologist. He made numerous discoveries, including the LOV-domain photoreceptor phototropin. Winslow Briggs, who was also a naturalist and gifted pianist, inspired and promoted the work of generations of young scientists - as mentor, colleague and friend.

Soybean is a widely grown grain legume and one of the most important economic crop species. Brassinosteroids play a crucial role in plant vegetative growth and reproductive development. However, it remains unclear how BRs regulate the developmental processes in soybean, and the molecular mechanism underlying soybean early development is largely unexplored. In this study, we first characterized how soybean early vegetative growth was specifically regulated by the BR biosynthesis inhibitor propiconazole; this characterization included shortened root and shoot lengths, reduced leaf area, and decreased chlorophyll content. In addition, the growth inhibition induced by Pcz could be rescued by exogenous brassinolide application. The RNA-seq technique was employed to investigate the BR regulatory networks during soybean early vegetative development. Identification and analysis of differentially expressed genes indicated that BRs orchestrate a wide range of cellular activities and biological processes in soybean under various BR concentrations. The regulatory networks between BRs and multiple hormones or stress-related pathways were investigated. The results provide a comprehensive view of the physiological functions of BRs and new insights into the molecular mechanisms at the transcriptional level of BR regulation of soybean early development.

Coordinating stress defense and plant growth is a survival strategy for adaptation to different environments that contains a series of processes, such as, cell growth, division and differentiation. However, little is known about the coordination mechanism for protein conformation change. A cyclophilin OsCYP20-2 with a variant interacts with SLENDER RICE1 (SLR1) and OsFSD2 in the nucleus and chloroplasts, respectively, to integrate chilling tolerance and cell elongation in rice (Oryza sativa) (FSD2, Fe-superoxide dismutase 2). Mass spectrum assay showed that OsNuCYP20-2 localized at the nucleus (nuclear located OsCYP20-2) was a new variant of OsCYP20-2 that truncated 71 amino-acid residues in N-terminal. The loss-of function OsCYP20-2 mutant showed sensitivity to chilling stress with accumulation of extra reactive oxygen species (ROS). In chloroplasts, the full-length OsCYP20-2 promotes OsFSD2 forming homodimers which enhance its activity, eliminating the accumulation of ROS under chilling stress. However, the mutant had shorter epidermal cells in comparison with wild-type Hwayoung (HY). In the nucleus, OsCYP20-2 caused conformation change of SLR1 to promote its degradation for cell elongation. Our data reveal a cyclophilin with a variant with dual-localization in chloroplasts and the nucleus, which mediate chilling tolerance and cell elongation.

The spatiotemporal balance between stem cell maintenance, proliferation, and differentiation determines the rate of root growth and is controlled by hormones, including auxin and brassinosteroid (BR). However, the spatial actions of BR and its interactions with auxin remain unclear in roots. Here, we show that oppositely patterned and antagonistic actions of BR and auxin maintain the stem cell balance and optimal root growth. We discover a pattern of low levels of nuclear-localized BR-activated transcription factor BZR1 in the stem cell niche and high BZR1 levels in the transition-elongation zone. This BZR1 pattern requires local BR catabolism and auxin synthesis, as well as BR signaling. Cell-type-specific expression of a constitutively active form of BZR1 confirms that the high and low levels of BZR1 are required for the normal cell behaviors in the elongation zone and quiescent center (QC), respectively. Comparison between BR-responsive, BZR1-targeted, auxin-responsive, and developmental zone-specific transcriptomes indicates that BZR1 mostly activates its target genes expressed in the transition-elongation zone, but represses genes in the QC and surrounding stem cells, and that BR and auxin have overall opposite effects on gene expression. Genetic and physiological interactions support that a balance between the antagonistic actions of BR and auxin is required for optimal root growth. These results demonstrate that the level and output specificity of BR signaling are spatially patterned and that, in contrast to their synergism in shoots, BR and auxin interact antagonistically in roots to control the spatiotemporal balance of stem cell dynamics required for optimal root growth.

plant growth is coordinately regulated by environmental and hormonal signals. Brassinosteroid (BR) plays essential roles in growth regulation by light and temperature, but the interactions between BR and these environmental signals remain poorly understood at the molecular level. Here, we show that direct interaction between the dark- and heat-activated transcription factor phytochrome-interacting factor4 (PIF4) and the BR-activated transcription factor BZR1 integrates the hormonal and environmental signals. BZR1 and PIF4 interact with each other in vitro and in vivo, bind to nearly 2,000 common target genes, and synergistically regulate many of these target genes, including the PRE family helix-loop-helix factors required for promoting cell elongation. Genetic analysis indicates that BZR1 and PIFs are interdependent in promoting cell elongation in response to BR, darkness or heat. These results show that the BZR1-PIF4 interaction controls a core transcription network, enabling plant growth co-regulation by the steroid and environmental signals.

SWI/SNF-type chromatin remodelers, such as BRAHMA (BRM), and H3K27 demethylases both have active roles in regulating gene expression at the chromatin level(1-5), but how they are recruited to specific genomic sites remains largely unknown. Here we show that RELATIVE OF EARLY FLOWERING 6 (REF6), a plant-unique H3K27 demethylase(6), targets genomic loci containing a CTCTGYTY motif via its zinc-finger (ZnF) domains and facilitates the recruitment of BRM. Genome-wide analyses showed that REF6 colocalizes with BRM at many genomic sites with the CTCTGYTY motif. Loss of REF6 results in decreased BRM occupancy at BRM-REF6 co-targets. Furthermore, REF6 directly binds to the CTCTGYTY motif in vitro, and deletion of the motif from a target gene renders it inaccessible to REF6 in vivo. Finally, we show that, when its ZnF domains are deleted, REF6 loses its genomic targeting ability. Thus, our work identifies a new genomic targeting mechanism for an H3K27 demethylase and demonstrates its key role in recruiting the BRM chromatin remodeler.

Comparison of differential gene expression in WT (Col-0) and bsu-q, and flg22-responsive genes in Col-0 and bsu-q.