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Climate change is predicted to be a major threat to crop yield due to increasing global temperatures and periods of unpredictable rainfall. Therefore, it is important to identify some new genes that can help plants cope with drought stress. In this study, a drought-induced homeodomain-leucine zipper (HD-Zip) I gene, ZmHDZ4, was isolated from maize and characterized for its role in drought stress. Transient expression experiments showed that ZmHDZ4 is localized to the nucleus. Yeast one-hybrid assays demonstrated that ZmHDZ4 has trans-activation activity, and that the minimal activation domain was ZmHDZ4-1. We found that overexpression of ZmHDZ4 in rice can enhance tolerance to drought and increase sensitivity to abscisic acid (ABA). Compared to wild-type plants, ZmHDZ4-expressing transgenic plants had lower relative electrolyte leakage (REL), lower malondialdehyde (MDA) levels, and increased proline contents under drought stress conditions, all of which may contribute to enhanced drought tolerance. Taken together, these results suggest that ZmHDZ4 functions as a transcriptional regulator that can positively affect plant drought tolerance. Thus, ZmHDZ4 is an excellent candidate gene with potential applications in molecular breeding to improve crop drought tolerance. [ABSTRACT FROM AUTHOR]

Key message: Overexpression in Arabidopsis of the maize shikimate kinase-like genes SKL1 and SKL2 enhances tolerance to drought stress. The shikimate pathway has been reported to play an important role in plant signaling, reproduction, and development. However, its role in abiotic stress has not yet been reported. Here, two shikimate kinase-like genes, SKL1 and SKL2, were cloned from maize and their functions in mediating drought tolerance were investigated. Transcript levels of ZmSKL1 and ZmSKL2 in roots and leaves were strongly induced by drought stress. Both proteins were localized in the chloroplast. Furthermore, compared to the wild-type, transgenic Arabidopsis plants overexpressing ZmSKL1 or ZmSKL2 exhibited improved drought stress tolerance through increases in relative water content and stomatal closure. Additionally, the transgenic lines showed reduced accumulation of reactive oxygen species as a results of increased antioxidant enzyme activity. Interestingly, overexpression of ZmSKL1 or ZmSKL2 also increased sensitivity to exogenous abscisic acid. In addition, the ROS-related and stress-responsive genes were activated in transgenic lines under drought stress. Moreover, ZmSKL1 and ZmSKL2 were found to separately interact with ZmASR3, which is an important regulatory protein in mediating drought tolerance, suggesting that ZmSKL1 and ZmSKL2, together with ZmASR3, are proteins that may confer drought tolerance as candidates in plant genetic breeding manipulations. [ABSTRACT FROM AUTHOR]

Abiotic stresses such as salinity and drought greatly impact the growth and production of crops worldwide. Here, a shikimate kinase-like 2 (SKL2) gene was cloned from rice and characterized for its regulatory function in salinity and drought tolerance. OsSKL2 was localized in the chloroplast, and its transcripts were significantly induced by drought and salinity stress as well as H2O2 and abscisic acid (ABA) treatment. Meanwhile, overexpression of OsSKL2 in rice increased tolerance to salinity, drought and oxidative stress by increasing antioxidant enzyme activity, and reducing levels of H2O2, malondialdehyde, and relative electrolyte leakage. In contrast, RNAi-induced suppression of OsSKL2 increased sensitivity to stress treatment. Interestingly, overexpression of OsSKL2 also increased sensitivity to exogenous ABA, with an increase in reactive oxygen species (ROS) accumulation. Moreover, OsSKL2 was found to physically interact with OsASR1, a well-known chaperone-like protein, which also exhibited positive roles in salt and drought tolerance. A reduction in ROS production was also observed in leaves of Nicotiana benthamiana showing transient co-expression of OsSKL2 with OsASR1. Taken together, these findings suggest that OsSKL2 together with OsASR1 act as important regulatory factors that confer salt and drought tolerance in rice via ROS scavenging. [ABSTRACT FROM AUTHOR]

High salinity seriously affects crop growth and yield. Abscisic acid-, stress-, and ripening-induced (ASR) proteins play an important role in plant responses to multiple abiotic stresses. In this study, we identified a new salt-induced ASR gene in rice (OsASR6) and functionally characterized its role in mediating salt tolerance. Transcript levels of OsASR6 were upregulated under salinity stress, H2O2 and abscisic acid (ABA) treatments. Nuclear and cytoplasmic localization of the OsASR6 protein were confirmed. Meanwhile, a transactivation activity assay in yeast demonstrated no self-activation ability. Furthermore, transgenic rice plants overexpressing OsASR6 showed enhanced salt and oxidative stress tolerance as a result of reductions in H2O2, malondialdehyde (MDA), Na/K and relative electrolyte leakage. In contrast, OsASR6 RNAi transgenic lines showed opposite results. A higher ABA content was also measured in the OsASR6 overexpressing lines compared with the control. Moreover, OsNCED1, a key enzyme of ABA biosynthesis, was found to interact with OsASR6. Collectively, these results suggest that OsASR6 serves primarily as a functional protein, enhancing tolerance to salt stress, representing a candidate gene for genetic manipulation of new salinity-resistant lines in rice. [ABSTRACT FROM AUTHOR]

Abscisic acid-, stress-, and ripening-induced (ASR) proteins in plants play a significant role in plant response to diverse abiotic stresses. However, the functions of ASR genes in maize remain unclear. In the present study, we identified a novel drought-induced ASR gene in maize (ZmASR1) and functionally characterized its role in mediating drought tolerance. The transcription of ZmASR1 was upregulated under drought stress and abscisic acid (ABA) treatment, and the ZmASR1 protein was observed to exhibit nuclear and cytoplasmic localization. Moreover, ZmASR1 knockout lines generated with the CRISPR–Cas9 system showed lower ROS accumulation, higher ABA content, and a higher degree of stomatal closure than wild-type plants, leading to higher drought tolerance. Transcriptome sequencing data indicated that the significantly differentially expressed genes in the drought treatment group were mainly enriched in ABA signal transduction, antioxidant defense, and photosynthetic pathway. Taken together, the findings suggest that ZmASR1 negatively regulates drought tolerance and represents a candidate gene for genetic manipulation of drought resistance in maize. • A novel ASR gene was firstly cloned and characterize from maize. • ZmASR1 knockout lines showed enhanced drought stress tolerance in maize. • ZmASR1 knockout lines showed altered the expression of stress-response related genes. [ABSTRACT FROM AUTHOR]

Abscisic acid (ABA)-, stress-, and ripening-induced (ASR) proteins are reported to be involved in drought stress responses. However, the function of maize ASR genes in enhancing drought tolerance is not known. Here, nine maize ASR members were cloned, and the molecular features of these genes were analyzed. Phenotype results of overexpression of maize ZmASR3 gene in Arabidopsis showed lower malondialdehyde (MDA) levels and higher relative water content (RWC) and proline content than the wild type under drought conditions, demonstrating that ZmASR3 can improve drought tolerance. Further experiments showed that ZmASR3-overexpressing transgenic lines displayed increased stomatal closure and reduced reactive oxygen species (ROS) accumulation by increasing the enzyme activities of superoxide dismutase (SOD) and catalase (CAT) under drought conditions. Moreover, overexpression of ZmASR3 in Arabidopsis increased ABA content and reduced sensitivity to exogenous ABA in both the germination and post-germination stages. In addition, the ROS-related, stress-responsive, and ABA-dependent pathway genes were activated in transgenic lines under drought stress. Taken together, these results suggest that ZmASR3 acts as a positive regulator of drought tolerance in plants. [ABSTRACT FROM AUTHOR]