BIC1 acts as a transcriptional coactivator to promote brassinosteroid signaling and plant growth.

The BRASSINAZOLE-RESISTANT 1 (BZR1) transcription factor family plays an essential role in plant brassinosteroid (BR) signaling, but the signaling mechanism through which BZR1 and its homologs cooperate with certain coactivators to facilitate transcription of target genes remains incompletely understood. In this study, we used an efficient protein interaction screening system to identify blue-light inhibitor of cryptochromes 1 (BIC1) as a new BZR1-interacting protein in Arabidopsis thaliana. We show that BIC1 positively regulates BR signaling and acts as a transcriptional coactivator for BZR1-dependent activation of BR-responsive genes. Simultaneously, BIC1 interacts with the transcription factor PIF4 to synergistically and interdependently activate expression of downstream genes including PIF4 itself, and to promote plant growth. Chromatin immunoprecipitation assays demonstrate that BIC1 and BZR1/PIF4 interdependently associate with the promoters of common target genes. In addition, we show that the interaction between BIC1 and BZR1 is evolutionally conserved in the model monocot plant Triticum aestivum (bread wheat). Together, our results reveal mechanistic details of BR signaling mediated by a transcriptional activation module BIC1/BZR1/PIF4 and thus provide new insights into the molecular mechanisms underlying the integration of BR and light signaling in plants.

Sequential activation of strigolactone and salicylate biosynthesis promotes leaf senescence.

Leaf senescence is a complex process strictly regulated by various external and endogenous factors. However, the key signaling pathway mediating leaf senescence remains unknown. Here, we show that Arabidopsis SPX1/2 negatively regulate leaf senescence genetically downstream of the strigolactone (SL) pathway. We demonstrate that the SL receptor AtD14 and MAX2 mediate the age-dependent degradation of SPX1/2. Intriguingly, we uncover an age-dependent accumulation of SLs in leaves via transcriptional activation of SL biosynthetic genes by the transcription factors (TFs) SPL9/15. Furthermore, we reveal that SPX1/2 interact with the WRKY75 subclade TFs to inhibit their DNA-binding ability and thus repress transcriptional activation of salicylic acid (SA) biosynthetic gene SA Induction-Deficient 2, gating the age-dependent SA accumulation in leaves at the leaf senescence onset stage. Collectively, our new findings reveal a signaling pathway mediating sequential activation of SL and salicylate biosynthesis for the onset of leaf senescence in Arabidopsis.

OsNF-YB7 inactivates OsGLK1 to inhibit chlorophyll biosynthesis in rice embryo.

As a master regulator of seed development, Leafy Cotyledon 1 (LEC1) promotes chlorophyll (Chl) biosynthesis in Arabidopsis, but the mechanism underlying this remains poorly understood. Here, we found that loss of function of OsNF-YB7, a LEC1 homolog of rice, leads to chlorophyllous embryo, indicating that OsNF-YB7 plays an opposite role in Chl biosynthesis in rice compared with that in Arabidopsis. OsNF-YB7 regulates the expression of a group of genes responsible for Chl biosynthesis and photosynthesis by directly binding to their promoters. In addition, OsNF-YB7 interacts with Golden 2-Like 1 (OsGLK1) to inhibit the transactivation activity of OsGLK1, a key regulator of Chl biosynthesis. Moreover, OsNF-YB7 can directly repress OsGLK1 expression by recognizing its promoter in vivo, indicating the involvement of OsNF-YB7 in multiple regulatory layers of Chl biosynthesis in rice embryo. We propose that OsNF-YB7 functions as a transcriptional repressor to regulate Chl biosynthesis in rice embryo.

The blue light receptor CRY1 interacts with GID1 and DELLA proteins to repress gibberellin signaling and plant growth.

Improvements in plant architecture, such as reduced plant height under high-density planting, are important for agricultural production. Light and gibberellin (GA) are essential external and internal cues that affect plant architecture. In this study, we characterize the direct interaction of distinct receptors that link light and GA signaling in Arabidopsis (Arabidopsis thaliana) and wheat (Triticum aestivum L.). We show that the light receptor CRY1 represses GA signaling through interaction with all five DELLA proteins and promotion of RGA protein accumulation in Arabidopsis. Genetic analysis shows that CRY1-mediated growth repression is achieved by means of the DELLA proteins. Interestingly, we find that CRY1 also directly interacts with the GA receptor GID1 to competitively inhibit the GID1-GAI interaction. We also show that overexpression of TaCRY1a reduces plant height and coleoptile growth in wheat and that TaCRY1a interacts with both TaGID1 and Rht1 to competitively attenuate the TaGID1-Rht1 interaction. Based on these findings, we propose that the photoreceptor CRY1 competitively inhibits the GID1-DELLA interaction, thereby stabilizing DELLA proteins and enhancing their repression of plant growth.

Physiological and proteomic analysis of maize seedling response to water deficiency stress.

Low water availability is a major abiotic factor limiting photosynthesis and the growth and yield of crops. Maize (Zea mays) is among the most drought-sensitive cereal crops. Herein, the physiological and proteomic changes of maize seedlings caused by polyethylene-glycol-induced water deficit were analyzed. The results showed that malondialdehyde and proline contents increased continuously in the treated seedlings. Soluble sugar content and superoxide dismutase activity were upregulated initially but became downregulated under prolonged water deficit. A total of 104 proteins were found to be differentially accumulated under water stress. The identified proteins were mainly involved in photosynthesis, carbohydrate metabolism, stress defense, energy production, and protein metabolism. Interestingly, substantial incongruence between protein and transcript levels was observed, indicating that gene expression in water-stressed maize seedlings is controlled by complex mechanisms. Finally, we propose a hypothetical model that includes the different molecular, physiological, and biochemical changes that occurred during the response and tolerance of maize seedlings to water deficiency. Our study provides valuable insight for further research into the overall mechanisms underlying drought response and tolerance in maize and other plants.