Transcription factor GLK1 promotes anthocyanin biosynthesis via an MBW complex-dependent pathway in Arabidopsis thaliana.

Anthocyanins are important natural plant pigments and play diverse roles in plant growth and adaptation. Anthocyanins function as screens to protect photosynthetic tissues from photoinhibition. However, the regulatory mechanisms underlying the biosynthesis and spatial accumulation pattern of anthocyanins remain some unresolved issues. Here, we demonstrate that the GARP-type transcription factor GOLDEN2-LIKE 1 (GLK1) functions as a positive factor in anthocyanin accumulation. GLK1 enhances the transcriptional activation activities of MYB75, MYB90, and MYB113 via direct protein-protein interactions to increase the expression of anthocyanin-specific biosynthetic genes. Anthocyanins accumulate in an acropetal manner in Arabidopsis. We also found that the expression pattern of GLK1 overall mimicked the accumulation pattern of anthocyanin from the base of the main stem to the shoot apex. Based on these findings, we established a working model for the role of GLK1 in anthocyanin accumulation and propose that GLK1 mediates the spatial distribution pattern of anthocyanins by affecting the transcriptional activation activities of MYB75, MYB90, and MYB113.

Mitochondrial alternative oxidase enhanced ABA-mediated drought tolerance in Solanum lycopersicum.

The phytohormone abscisic acid (ABA) plays essential roles in modulating drought stress responses. Mitochondrial alternative oxidase (AOX) is critical for reactive oxygen species (ROS) scavenging in drought stress responses. However, whether ABA signal in concert with AOX to moderate drought stress response remains largely unclear. In our study, we uncover the positive role of AOX in ABA-mediated drought tolerance in tomato (Solanum lycopersicum). Here, we report that ABA participates in the regulation of alternative respiration, and the increased AOX was found to improve drought tolerance by reducing total ROS accumulation. We also found that transcription factor ABA response element-binding factor 1 (SlAREB1) can directly bind to the promoter of AOX1a to activate its transcription. Virus-induced gene silencing (VIGS) of SlAREB1 compromised the ABA-induced alternative respiratory pathway, disrupted redox homeostasis and decreased plant resistance to drought stress, while overexpression of AOX1a in TRV2-SlAREB1 plants partially rescued the severe drought phenotype. Taken together, our results indicated that AOX1a plays an essential role in ABA-mediated drought tolerance partially in a SlAREB1-dependent manner, providing new insights into how ABA modulates ROS levels to cope with drought stress by AOX.

Nitrogen-inducible GLK1 modulates phosphate starvation response via the PHR1-dependent pathway.

Phosphorus (P) is a limiting nutrient for plant growth and productivity. Thus, a deep understanding of the molecular mechanisms of plants' response to phosphate starvation is significant when breeding crops with higher phosphorus-use efficiency. Here, we found that GARP-type transcription factor GLK1 acted as a positive regulator for phosphate-starvation response (PSR) via the PHR1-dependent pathway in Arabidopsis thaliana. GLK1 increased the transcription activity of PHR1 through the direct physical interaction and regulated the multiple responses to inorganic orthophosphate (Pi) starvation. Nitrogen (N) is a key factor in the regulation of PSR. We also found that the N status controlled the function of the GLK1-PHR1 signaling module under Pi-deficient (LP) conditions by regulating the accumulation of GLK1 and PHR1. Ultimately, we showed that the presence of GLK1 effectively promoted the protein accumulation of PHR1 at low N concentrations, and this action was helpful to maintain the activation of PSR. According to these findings, we establish the working model for GLK1 in PSR and propose that GLK1 mediates the interaction between N and P by influencing the effect of N on PHR1 in Arabidopsis thaliana.

Brassinosteroids enhance BES1-required thermomemory in Arabidopsis thaliana.

Heat stress (HS) caused by ambient high temperature poses a threat to plants. In the natural and agricultural environment, plants often encounter repeated and changeable HS. Moderate HS primes plants to establish a molecular 'thermomemory' that enables plants to withstand a later-and possibly more extreme-HS attack. Recent years, brassinosteroids (BRs) have been implicated in HS response, whereas the information is lacking on whether BRs signal transduction modulates thermomemory. Here, we uncover the positive role of BRs signalling in thermomemory of Arabidopsis thaliana. Heat priming induces de novo synthesis and nuclear accumulation of BRI1-Ethyl methyl sulfon-SUPPRESSOR (BES1), which is the key regulator of BRs signalling. BRs promote the accumulation of dephosphorylated BES1 during memory phase, and stoppage of BRs synthesis impairs dephosphorylation. During HS memory, BES1 is required to maintain sustained induction of HS memory genes and directly targets APX2 and HSFA3 for activation. In summary, our results reveal a BES1-required, BRs-enhanced transcriptional control module of thermomemory in Arabidopsis thaliana.