Crosstalk between signaling pathways is an important feature of complex regulatory networks. How signal crosstalk circuits are tailored to suit different needs of various cell types remains a mystery in biology. Brassinosteroid (BR) and abscisic acid (ABA) antagonistically regulate many aspects of plant growth and development through direct interactions between components of the two signaling pathways. Here, we show that BR and ABA synergistically regulate stomatal closure through crosstalk between the BR-activated kinase CDG1-LIKE1 (CDL1) and the OPEN STOMATA1 (OST1) of the ABA signaling pathway in Arabidopsis thaliana. We demonstrate that the cdl1 mutant displayed reduced sensitivity to ABA in a stomatal closure assay, similar to the ost1 mutant. CDL1 and the BR receptor BR-INSENSITIVE1, but not other downstream components of the BR signaling pathway, were required for BR regulation of stomatal movement. Genetic and biochemical experiments demonstrated that CDL1 activates OST1 by phosphorylating it on residue Ser-7. BR increased phosphorylation of OST1, and the BR-induced OST1 activation was abolished in cdl1 mutants. Moreover, we found that ABA activates CDL1 in an OST1-dependent manner. Taken together, our findings illustrate a cell-type-specific BR signaling branch through which BR acts synergistically with ABA in regulating stomatal closure.

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.

Theoretical and eddy covariance studies demonstrate that aerosol-loading stimulates canopy photosynthesis, but field evidence for the aerosol effect on tree growth is limited. Here, we measured in situ daily stem growth rates of aspen trees under a wide range of aerosol-loading in China. The results showed that daily stem growth rates were positively correlated with aerosol-loading, even at exceptionally high aerosol levels. Using structural equation modeling analysis, we showed that variations in stem growth rates can be largely attributed to two environmental variables covarying with aerosol loading: diffuse fraction of radiation and vapor pressure deficit (VPD). Furthermore, we found that these two factors influence stem growth by influencing photosynthesis from different parts of canopy. Using field observations and a mechanistic photosynthesis model, we demonstrate that photosynthetic rates of both sun and shade leaves increased under high aerosol-loading conditions but for different reasons. For sun leaves, the photosynthetic increase was primarily attributed to the concurrent lower VPD; for shade leaves, the positive aerosol effect was tightly connected with increased diffuse light. Overall, our study provides the first field evidence of increased tree growth under high aerosol loading. We highlight the importance of understanding biophysical mechanisms of aerosol-meteorology interactions, and incorporating the different pathways of aerosol effects into earth system models to improve the prediction of large-scale aerosol impacts, and the associated vegetation-mediated climate feedbacks.

BackgroundBrassinosteroids (BRs) play a crucial role in plant vegetative growth and reproductive development. The transcription factors BZR1 and BES1/BZR2 are well characterized as downstream regulators of the BR signaling pathway in Arabidopsis and rice. Soybean contains four BZR1-like proteins (GmBZLs), and it was reported that GmBZL2 plays a conserved role in BR signaling regulation. However, the roles of other GmBZLs have not been thoroughly studied, and the targets of GmBZLs in soybean remain unclear.ResultsIn this study, we first characterized GmBZL3 in soybean from gene expression patterns, conserved domains in coding sequences, and genomic replication times of four GmBZL orthologous. The results indicated that GmBZL3 might play conserved roles during soybean development. The overexpression of GmBZL3(P219L) in the Arabidopsis BR-insensitive mutant bri1-5 partially rescued the phenotypic defects including BR-insensitivity, which provides further evidence that GmBZL3 functions are conserved between soybean and the homologous Arabidopsis genes. In addition, the identification of the GmBZL3 target genes through ChIP-seq technology revealed that BR has broad roles in soybean and regulates multiple pathways, including other hormone signaling, disease-related, and immunity response pathways. Moreover, the BR-regulated GmBZL3 target genes were further identified, and the results demonstrate that GmBZL3 is a major transcription factor responsible for BR-regulated gene expression and soybean growth. A comparison of GmBZL3 and AtBZR1/BES1 targets demonstrated that GmBZL3 might play conserved as well as specific roles in the soybean BR signaling network. Finally, the identification of two natural soybean varieties of the GmBZL3 mutantion by SNP analysis could facilitate the understanding of gene function during soybean development in the future.ConclusionsWe illustrate here that GmBZL3 orchestrates a genome-wide transcriptional response that underlies BR-mediated soybean early vegetative growth, and our results support that BRs play crucial regulatory roles in soybean morphology and gene expression levels.

replicate 2 Total reads were mapped to the Arabidopsis thaliana genome (TAIR10, www.arabidopsis.org) using TopHat v1.4.0, with parameters --min-segment-intron 40 --max-segment-intron 2000 --bowtie --no-novel-juncs --read-mismatches 2 -GRead counts for each gene were quantified using HTSeq-count with union mode.Genome_build: TAIR10, www.arabidopsis.orgSupplementary_files_format_and_content: tab-delimited text files include read count values for each Sample

replicate 2 Total reads were mapped to the Arabidopsis thaliana genome (TAIR10, www.arabidopsis.org) using TopHat v1.4.0, with parameters --min-segment-intron 40 --max-segment-intron 2000 --bowtie --no-novel-juncs --read-mismatches 2 -GRead counts for each gene were quantified using HTSeq-count with union mode.Genome_build: TAIR10, www.arabidopsis.orgSupplementary_files_format_and_content: tab-delimited text files include read count values for each Sample

replicate 2 Total reads were mapped to the Arabidopsis thaliana genome (TAIR10, www.arabidopsis.org) using TopHat v1.4.0, with parameters --min-segment-intron 40 --max-segment-intron 2000 --bowtie --no-novel-juncs --read-mismatches 2 -GRead counts for each gene were quantified using HTSeq-count with union mode.Genome_build: TAIR10, www.arabidopsis.orgSupplementary_files_format_and_content: tab-delimited text files include read count values for each Sample

replicate 2 Total reads were mapped to the Arabidopsis thaliana genome (TAIR10, www.arabidopsis.org) using TopHat v1.4.0, with parameters --min-segment-intron 40 --max-segment-intron 2000 --bowtie --no-novel-juncs --read-mismatches 2 -GRead counts for each gene were quantified using HTSeq-count with union mode.Genome_build: TAIR10, www.arabidopsis.orgSupplementary_files_format_and_content: tab-delimited text files include read count values for each Sample

replicate 1 Total reads were mapped to the Arabidopsis thaliana genome (TAIR10, www.arabidopsis.org) using TopHat v1.4.0, with parameters --min-segment-intron 40 --max-segment-intron 2000 --bowtie --no-novel-juncs --read-mismatches 2 -GRead counts for each gene were quantified using HTSeq-count with union mode.Genome_build: TAIR10, www.arabidopsis.orgSupplementary_files_format_and_content: tab-delimited text files include read count values for each Sample

replicate 2 Total reads were mapped to the Arabidopsis thaliana genome (TAIR10, www.arabidopsis.org) using TopHat v1.4.0, with parameters --min-segment-intron 40 --max-segment-intron 2000 --bowtie --no-novel-juncs --read-mismatches 2 -GRead counts for each gene were quantified using HTSeq-count with union mode.Genome_build: TAIR10, www.arabidopsis.orgSupplementary_files_format_and_content: tab-delimited text files include read count values for each Sample