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• TGACG-BINDING FACTORs (TGAs) control the developmental or defense-related processes. In Arabidopsis thaliana, the functions of at least TGA2 and PERIANTHIA (PAN) can be repressed by interacting with CC-type glutaredoxins, which have the potential to control the redox state of target proteins. As TGA1 can be redox modulated in planta, we analyzed whether some of the 21 CC-type glutaredoxins (ROXYs) encoded in the Arabidopsis genome can influence TGA1 activity in planta and whether the redox active cysteines of TGA1 are functionally important. • We show that the tga1 tga4 mutant and plants ectopically expressing ROXY8 or ROXY9 are impaired in hyponastic growth. As expression of ROXY8 and ROXY9 is activated upon transfer of plants from hyponasty-inducing low light to normal light, they might interfere with the growth-promoting function of TGA1/TGA4 to facilitate reversal of hyponastic growth. • The redox-sensitive cysteines of TGA1 are not required for induction or reversal of hyponastic growth. • TGA1 and TGA4 interact with ROXYs 8, 9, 18, and 19/GRX480, but ectopically expressed ROXY18 and ROXY19/GRX480 do not interfere with hyponastic growth. Our results therefore demonstrate functional specificities of individual ROXYs for distinct TGAs despite promiscuous protein–protein interactions and point to different repression mechanisms, depending on the TGA/ROXY combination.

Summary Glutaredoxins (GRXs) are essential for reactive oxygen species (ROS) homeostasis in responses of plants to environment changes. We previously identified several drought‐responsive CC‐type GRXs in cassava, an important tropical crop. However, how CC‐type GRX regulates ROS homeostasis of cassava under drought stress remained largely unknown. Here, we report that a drought‐responsive CC‐type GRX, namely MeGRXC3, was associated with activity of catalase in the leaves of 100 cultivars (or unique unnamed genotypes) of cassava under drought stress. MeGRXC3 negatively regulated drought tolerance by modulating drought‐ and abscisic acid‐induced stomatal closure in transgenic cassava. It antagonistically regulated hydrogen peroxide (H2O2) accumulation in epidermal cells and guard cells. Moreover, MeGRXC3 interacted with two catalases of cassava, MeCAT1 and MeCAT2, and regulated their activity in vivo. Additionally, MeGRXC3 interacts with a cassava TGA transcription factor, MeTGA2, in the nucleus, and regulates the expression of MeCAT7 through a MeTGA2‐MeMYB63 pathway. Overall, we demonstrated the roles of MeGRXC3 in regulating activity of catalase at both transcriptional and post‐translational levels, therefore involving in ROS homeostasis and stomatal movement in responses of cassava to drought stress. Our study provides the first insights into how MeGRXC3 may be used in molecular breeding of cassava crops.

Background We previously identified six drought-inducible CC-type glutaredoxins in cassava cultivars, however, less is known about their potential role in the molecular mechanism by which cassava adapted to abiotic stress. Results Herein, we investigate one of cassava drought-responsive CC-type glutaredoxins, namely MeGRXC3 , that involved in regulation of mannitol-induced inhibition on seed germination and seedling growth in transgenic Arabidopsis . MeGRXC3 overexpression up-regulates several stress-related transcription factor genes, such as PDF1.2 , ERF6 , ORA59, DREB2A , WRKY40 , and WRKY53 in Arabidopsis . Protein interaction assays show that MeGRXC3 interacts with Arabidopsis TGA2 and TGA5 in the nucleus. Eliminated nuclear localization of MeGRXC3 failed to result mannitol-induced inhibition of seed germination and seedling growth in transgenic Arabidopsis. Mutation analysis of MeGRXC3 indicates the importance of conserved motifs for its transactivation activity in yeast. Additionally, these motifs are also indispensable for its functionality in regulating mannitol-induced inhibition of seed germination and enhancement of the stress-related transcription factors in transgenic Arabidopsis . Conclusions MeGRXC3 overexpression confers mannitol sensitivity in transgenic Arabidopsis possibly through interaction with TGA2/5 in the nucleus, and nuclear activity of MeGRXC3 is required for its function.

Background CC-type glutaredoxins (GRXs) are plant-specific glutaredoxin, play regulatory roles in response of biotic and abiotic stress. However, it is not clear whether the CC-type GRXs are involve in drought response in cassava ( Manihot esculenta ), an important tropical tuber root crop. Results Herein, genome-wide analysis identified 18 CC-type GRXs in the cassava genome, of which six (namely MeGRXC3, C4, C7, C14, C15 , and C18 ) were induced by drought stress in leaves of two cassava cultivars Argentina 7 (Arg7) and South China 124 (SC124). Exogenous abscisic acid (ABA) application induced the expression of all the six CC-type GRXs in leaves of both Arg7 and SC124 plants. Overexpression of MeGRXC15 in Arabidopsis (Col-0) increases tolerance of ABA on the sealed agar plates, but results in drought hypersensitivity in soil-grown plants. The results of microarray assays show that MeGRXC15 overexpression affected the expression of a set of transcription factors which involve in stress response, ABA, and JA/ET signalling pathway. The results of protein interaction analysis show that MeGRXC15 can interact with TGA5 from Arabidopsis and MeTGA074 from cassava. Conclusions CC-type glutaredoxins play regulatory roles in cassava response to drought possibly through ABA signalling pathway.

Global maize cultivation is often adversely affected by drought stress. The CC-type glutaredoxin (GRX) genes form a plant-specific subfamily that regulate plant growth and respond to environmental stresses. However, how maize CC-type GRX (ZmGRXCC) genes respond to drought stress remains unclear. We performed a TBLASTN search to identify ZmGRXCCs in the maize genome and verified the identified sequences using the NCBI conservative domain database (CDD). We further established a phylogenetic tree using Mega7 and surveyed known cis-elements in the promoters of ZmGRXCCs using the PlantCARE database. We found twenty-one ZmGRXCCs in the maize genome by a genome-wide investigation and compared their phylogenetic relationships with rice, maize, and Arabidopsis. The analysis of their redox active sites showed that most of the 21 ZmGRXCCs share similar structures with their homologs. We assessed their expression at young seedlings and adult leaves under drought stress and their expression profiles in 15 tissues, and found that they were differentially expressed, indicating that different ZmGRXCC genes have different functions. Notably, ZmGRXCC14 is up-regulated at seedling, V12, V14, V16, and R1 stages. Importantly, significant associations between genetic variation in ZmGRXCC14 and drought tolerance are found at the seedling stage. These results will help to advance the study of the function of ZmGRXCCs genes under drought stress and understand the mechanism of drought resistance in maize.

Glutaredoxins (GRXs) are small glutathione dependent oxidoreductases that belong to the Thioredoxin (TRX) superfamily and catalyze the reduction of disulfide bonds of their substrate proteins. Plant GRXs include three different groups based on the motif sequence, namely CPYC, CGFS, and CC-type proteins. The rice CC-type proteins, OsGRX6 was identified during the screening for genes whose expression changes depending on the level of available nitrate. Overexpression of OsGRX6 in rice displayed a semi-dwarf phenotype. The OsGRX6 overexpressors contain a higher nitrogen content than the wild type, indicating that OsGRX6 plays a role in homeostatic regulation of nitrogen use. Consistent with this, OsGRX6 overexpressors displayed delayed chlorophyll degradation and senescence compared to the wild type plants. To examine if the growth defect of these transgenic lines attribute to disturbed plant hormone actions, plant hormone levels were measured. The levels of two cytokinins (CKs), 2-isopentenyladenine and trans-zeatin, and gibberellin A1 (GA1) were increased in these lines. We also found that these transgenic lines were less sensitive to exogenously applied GA, suggesting that the increase in GA1 is a result of the feedback regulation. These data suggest that OsGRX6 affects hormone signaling and nitrogen status in rice plants.