Analysis of the APX, PGD1 and R1G1B constitutive gene promoters in various organs over three homozygous generations of transgenic rice plants

CRISPR-Cas technology secures sustainability through its applications: a review in green biotechnology

The CRISPR-Cas system's applications in biotechnology offer a promising avenue for addressing pressing global challenges, such as climate change, environmental pollution, the energy crisis, and the food crisis, thereby advancing sustainability. The ever-growing demand for food due to the projected population of around 9.6 billion by 2050 requires innovation in agriculture. CRISPR-Cas technology emerges as a powerful solution, enhancing crop varieties, optimizing yields, and improving resilience to stressors. It offers multiple gene editing, base editing, and prime editing, surpassing conventional methods. CRISPR-Cas introduces disease and herbicide resistance, high-yielding, drought-tolerant, and water-efficient crops to address rising water utilization and to improve the efficiency of agricultural practices which promise food sustainability and revolutionize agriculture for the benefit of future generations. The application of CRISPR-Cas technology extends beyond agriculture to address environmental challenges. With the adverse impacts of climate change and pollution endangering ecosystems, there is a growing need for sustainable solutions. The technology's potential in carbon capture and reduction through bio-sequestration is a pivotal strategy for combating climate change. Genomic advancements allow for the development of genetically modified organisms, optimizing biofuel and biomaterial production, and contributing to a renewable and sustainable energy future. This study reviews the multifaceted applications of CRISPR-Cas technology in the agricultural and environmental fields and emphasizes its potential to secure a sustainable future.

Rice NAC17 transcription factor enhances drought tolerance by modulating lignin accumulation

Land plants have developed a comprehensive system to cope with the drought stress, and it is operated by intricate signaling networks, including transcriptional regulation. Herein, we identified the function of OsNAC17, a member of NAC (NAM, ATAF, and CUC2) transcription factor family, in drought tolerance. OsNAC17 is localized to the nucleus, and its expression was significantly induced under drought conditions. A transactivation assay in yeast revealed that the OsNAC17 is a transcriptional activator, harboring an activation domain in the C-terminal region. Overexpressing (OsNAC17^OX) transgenic plants showed drought-tolerant, and knock-out (OsNAC17^KO) plants exhibited drought susceptible phenotype compared to non-transgenic plants. Further investigation revealed that OsNAC17 positively regulates several lignin biosynthetic genes and promotes lignin accumulation in leaves and roots. Together, our results show that OsNAC17 contributes to drought tolerance through lignin biosynthesis in rice.

Tissue-specific enhancement of OsRNS1 with root-preferred expression is required for the increase of crop yield

INTRODUCTION

Root development is a fundamental process that supports plant survival and crop productivity. One of the essential factors to consider when developing biotechnology crops is the selection of a promoter that can optimize the spatial-temporal expression of introduced genes. However, there are insufficient cases of suitable promoters in crop plants, including rice.

OBJECTIVES

This study aimed to verify the usefulness of a new rice root-preferred promoter to optimize the function of a target gene with root-preferred expression in rice.

METHODS

osrns1 mutant had defects in root development based on T-DNA insertional mutant screening and CRISPR technology. To optimize the function of OsRNS1, we generated OsRNS1-overexpression plants under two different promoters: a whole-plant expression promoter and a novel root-preferred expression promoter. Root growth, yield-related agronomic traits, RNA-seq, and reactive oxygen species (ROS) accumulation were analyzed for comparison.

RESULTS

OsRNS1 was found to be involved in root development through T-DNA insertional mutant analysis and gene editing mutant analysis. To understand the gain of function of OsRNS1, pUbi1::OsRNS1 was generated for the whole-plant expression, and both root growth defects and overall growth defects were found. To overcome this problem, a root-preferential overexpression line using Os1-CysPrxB promoter (Per) was generated and showed an increase in root length, plant height, and grain yield compared to wild-type (WT). RNA-seq analysis revealed that the response to oxidative stress-related genes was significantly up-regulated in both overexpression lines but was more obvious in pPer::OsRNS1. Furthermore, ROS levels in the roots were drastically decreased in pPer::OsRNS1 but were increased in the osrns1 mutants compared to WT.

CONCLUSION

The results demonstrated that the use of a root-preferred promoter effectively optimizes the function of OsRNS1 and is a useful strategy for improving root-related agronomic traits as well as ROS regulation.

Transcriptional activation of rice CINNAMOYL-CoA REDUCTASE 10 by OsNAC5, contributes to drought tolerance by modulating lignin accumulation in roots

Drought is a common abiotic stress for terrestrial plants and often affects crop development and yield. Recent studies have suggested that lignin plays a crucial role in plant drought tolerance; however, the underlying molecular mechanisms are still largely unknown. Here, we report that the rice (Oryza sativa) gene CINNAMOYL-CoA REDUCTASE 10 (OsCCR10) is directly activated by the OsNAC5 transcription factor, which mediates drought tolerance through regulating lignin accumulation. CCR is the first committed enzyme in the monolignol synthesis pathway, and the expression of 26 CCR genes was observed to be induced in rice roots under drought. Subcellular localisation assays revealed that OsCCR10 is a catalytically active enzyme that is localised in the cytoplasm. The OsCCR10 transcript levels were found to increase in response to abiotic stresses, such as drought, high salinity, and abscisic acid (ABA), and transcripts were detected in roots at all developmental stages. In vitro enzyme activity and in vivo lignin composition assay suggested that OsCCR10 is involved in H- and G-lignin biosynthesis. Transgenic rice plants overexpressing OsCCR10 showed improved drought tolerance at the vegetative stages of growth, as well as higher photosynthetic efficiency, lower water loss rates, and higher lignin content in roots compared to non-transgenic (NT) controls. In contrast, CRISPR/Cas9-mediated OsCCR10 knock-out mutants exhibited reduced lignin accumulation in roots and less drought tolerance. Notably, transgenic rice plants with root-preferential overexpression of OsCCR10 exhibited higher grain yield than NT controls plants under field drought conditions, indicating that lignin biosynthesis mediated by OsCCR10 contributes to drought tolerance.

Production of a structurally validated cyclotide in rice suspension cells is enabled by a supporting biosynthetic enzyme

We demonstrate the production of a structurally correct cyclotide in rice suspension cells with co-expression of a ligase-type AEP, which unlocks monocotyledons as production platforms to produce cyclotides. Cyclotides are a class of backbone-cyclic plant peptides that harbor a cystine knot composed of three disulfide bonds. These structural features make cyclotides particularly stable, and thus they have attracted significant attention for their use in biotechnological applications such as drug design. Currently, chemical synthesis is the predominant strategy to produce cyclotides for research purposes. However, synthetic production becomes costly both economically and environmentally at large scale. Plants offer an attractive alternative to chemical synthesis because of their lower cost and environmental footprint. In this study, rice suspension cells were engineered to produce the prototypical cyclotide, kalata B1 (kB1), a cyclotide with insecticidal properties from the African plant Oldenlandia affinis. Engineered rice cells produced structurally validated kB1 at yields of 64.21 µg/g (DW), which was dependent on the co-expression of a peptide ligase-competent asparaginyl endopeptidase OaAEP1_b from O. affinis. Without co-expression, kB1 was predominantly produced as linear peptide. Through HPLC-MS co-elution, reduction, alkylation, enzymatic digestion, and proton NMR analysis, kB1 produced in rice was shown to be structurally identical to native kB1. This study reports the first example of an engineered plant suspension cell culture with the required molecular machinery for efficient production and cyclisation of a heterologous cyclotide.

Overexpression of OsC3H10, a CCCH-Zinc Finger, Improves Drought Tolerance in Rice by Regulating Stress-Related Genes

CCCH zinc finger proteins are members of the zinc finger protein family, and are known to participate in the regulation of development and stress responses via the posttranscriptional regulation of messenger RNA in animals and yeast. However, the molecular mechanism of CCCHZF-mediated drought tolerance is not well understood. We analyzed the functions of OsC3H10, a member of the rice CCCHZF family. OsC3H10 is predominantly expressed in seeds, and its expression levels rapidly declined during seed imbibition. The expression of OsC3H10 was induced by drought, high salinity and abscisic acid (ABA). Subcellular localization analysis revealed that OsC3H10 localized not only in the nucleus but also to the processing bodies and stress granules upon stress treatment. Root-specific overexpression of OsC3H10 was insufficient to induce drought tolerance, while the overexpression of OsC3H10 throughout the entire plant enhanced the drought tolerance of rice plants. Transcriptome analysis revealed that OsC3H10 overexpression elevated the expression levels of genes involved in stress responses, including LATE EMBRYOGENESIS ABUNDANT PROTEINs (LEAs), PATHOGENESIS RELATED GENEs (PRs) and GERMIN-LIKE PROTEINs (GLPs). Our results demonstrated that OsC3H10 is involved in the regulation of the drought tolerance pathway by modulating the expression of stress-related genes.

Overexpression of Rice Expansin7 (Osexpa7) Confers Enhanced Tolerance to Salt Stress in Rice

Expansins are key regulators of cell-wall extension and are also involved in the abiotic stress response. In this study, we evaluated the function of OsEXPA7 involved in salt stress tolerance. Phenotypic analysis showed that OsEXPA7 overexpression remarkably enhanced tolerance to salt stress. OsEXPA7 was highly expressed in the shoot apical meristem, root, and the leaf sheath. Promoter activity of OsEXPA7:GUS was mainly observed in vascular tissues of roots and leaves. Morphological analysis revealed structural alterations in the root and leaf vasculature of OsEXPA7 overexpressing (OX) lines. OsEXPA7 overexpression resulted in decreased sodium ion (Na⁺) and accumulated potassium ion (K⁺) in the leaves and roots. Under salt stress, higher antioxidant activity was also observed in the OsEXPA7-OX lines, as indicated by lower reactive oxygen species (ROS) accumulation and increased antioxidant activity, when compared with the wild-type (WT) plants. In addition, transcriptional analysis using RNA-seq and RT-PCR revealed that genes involved in cation exchange, auxin signaling, cell-wall modification, and transcription were differentially expressed between the OX and WT lines. Notably, salt overly sensitive 1, which is a sodium transporter, was highly upregulated in the OX lines. These results suggest that OsEXPA7 plays an important role in increasing salt stress tolerance by coordinating sodium transport, ROS scavenging, and cell-wall loosening.

Cloning and Functional Analysis of Phosphoethanolamine Methyltransferase Promoter from Maize (Zea mays L.)

Betaine, a non-toxic osmoprotectant, is believed to accumulate considerably in plants under stress conditions to maintain the osmotic pressure and promote a variety of processes involved in growth and development. Phosphoethanolamine N-methyltransferase (PEAMT), a key enzyme for betaine synthesis, is reported to be regulated by its upstream promoter. In the present investigation, by using the transgenic approach, a 1048 bp long promoter region of ZmPEAMT gene from Zea mays was cloned and functionally characterized in tobacco. Computational analysis affirmed the existence of abiotic stress responsive cis-elements like ABRE, MYC, HST, LST etc., as well as pathogen, wound and phytohormone responsive motifs. For transformation in tobacco, four 5′-deletion constructs of 826 bp (P2), 642 bp (P3), 428 bp (P4) and 245 bp (P5) were constructed from the 1048 bp (P1) promoter fragment. The transgenic plants generated through a single event exhibited a promising expression of GUS reporter protein in the leaf tissues of treated with salt, drought, oxidative and cold stress as well as control plants. The GUS expression level progressively reduced from P1 to P5 in the leaf tissues, whereas a maximal expression was observed with the P3 construct in the leaves of control plants. The expression of GUS was noted to be higher in the leaves of osmotically- or salt-treated transgenic plants than that in the untreated (control) plants. An effective expression of GUS in the transgenic plants manifests that this promoter can be employed for both stress-inducible and constitutive expression of gene(s). Due to this characteristic, this potential promoter can be effectively used for genetic engineering of several crops.

Overexpression of OsNAC14 Improves Drought Tolerance in Rice

Plants have evolved to have sophisticated adaptation mechanisms to cope with drought stress by reprograming transcriptional networks through drought responsive transcription factors. NAM, ATAF1-2, and CUC2 (NAC) transcription factors are known to be associated with various developmental processes and stress tolerance. In this study, we functionally characterized the rice drought responsive transcription factor OsNAC14. OsNAC14 was predominantly expressed at meiosis stage but is induced by drought, high salinity, ABA, and low temperature in leaves. Overexpression of OsNAC14 resulted in drought tolerance at the vegetative stage of growth. Field drought tests demonstrated that OsNAC14 overexpressing transgenic rice lines exhibited higher number of panicle and filling rate compared to non-transgenic plants under drought conditions. RNA-sequencing analysis revealed that OsNAC14 overexpression elevated the expression of genes for stress response, DNA damage repair, defense related, and strigolactone biosynthesis. In addition, chromatin immunoprecipitation analysis confirmed the direct interaction of OsNAC14 with the promoter of OsRAD51A1, a key component in homologous recombination in DNA repair system. Collectively, these results indicate that OsNAC14 mediates drought tolerance by recruiting factors involved in DNA damage repair and defense response resulting in improved tolerance to drought.

Overexpression of OsERF48 causes regulation of OsCML16, a calmodulin-like protein gene that enhances root growth and drought tolerance

The AP2/ERF family is a plant-specific transcription factor family whose members have been associated with various developmental processes and stress tolerance. Here, we functionally characterized the drought-inducible OsERF48, a group Ib member of the rice ERF family with four conserved motifs, CMI-1, -2, -3 and -4. A transactivation assay in yeast revealed that the C-terminal CMI-1 motif was essential for OsERF48 transcriptional activity. When OsERF48 was overexpressed in an either a root-specific (ROX^OsERF48 ) or whole-body (OX^OsERF48 ) manner, transgenic plants showed a longer and denser root phenotype compared to the nontransgenic (NT) controls. When plants were grown on a 40% polyethylene glycol-infused medium under in vitro drought conditions, ROX^OsERF48 plants showed a more vigorous root growth than OX^OsERF48 and NT plants. In addition, the ROX^OsERF48 plants exhibited higher grain yield than OX^OsERF48 and NT plants under field-drought conditions. We constructed a putative OsERF48 regulatory network by cross-referencing ROX^OsERF48 root-specific RNA-seq data with a co-expression network database, from which we inferred the involvement of 20 drought-related genes in OsERF48-mediated responses. These included genes annotated as being involved in stress signalling, carbohydrate metabolism, cell-wall proteins and drought responses. They included, OsCML16, a key gene in calcium signalling during abiotic stress, which was shown to be a direct target of OsERF48 by chromatin immunoprecipitation-qPCR analysis and a transient protoplast expression assay. Our results demonstrated that OsERF48 regulates OsCML16, a calmodulin-like protein gene that enhances root growth and drought tolerance.

SP-LL-37, human antimicrobial peptide, enhances disease resistance in transgenic rice

Human LL-37 is a multifunctional antimicrobial peptide of cathelicidin family. It has been shown in recent studies that it can serve as a host's defense against influenza A virus. We now demonstrate in this study how signal peptide LL-37 (SP-LL-37) can be used in rice resistance against bacterial leaf blight and blast. We synthesized LL-37 peptide and subcloned in a recombinant pPZP vector with pGD1 as promoter. SP-LL-37 was introduced into rice plants by Agrobacterium mediated transformation. Stable expression of SP-LL-37 in transgenic rice plants was confirmed by RT-PCR and ELISA analyses. Subcellular localization of SP-LL-37-GFP fusion protein showed evidently in intercellular space. Our data on testing for resistance to bacterial leaf blight and blast revealed that the transgenic lines are highly resistant compared to its wildtype. Our results suggest that LL-37 can be further explored to improve wide-spectrum resistance to biotic stress in rice.

Principales promotores utilizados en la transformación genética de plantas

El conocimiento pleno de los promotores determina el éxito en la obtención de nuevos cultivares de plantas a través de técnicas biotecnológicas, ya que dicha secuencia del ADN regula la transcripción de otras regiones adyacentes o cercanas, encontrándose los siguientes promotores: constitutivos, tejido-específicos o estadio-específicos, inducibles y sintéticos. En esta revisión se resume de manera precisa los conceptos, ventajas y limitaciones de los distintos tipos de promotores, con ejemplos claros de ello.Palabras clave: promotor, biotecnología vegetal, transcripción genética.

A novel cis-acting element in the GmERF3 promoter contributes to inducible gene expression in soybean and tobacco after wounding

KEY MESSAGE

Using in silico and functional analyses, we cloned and validated the expression profile of an inducible soybean promoter (GmERF3) along with its novel wound-induced and delayed expression (WIDE) element. Promoters and their contributing promoter elements are the main regulators of gene expression at the transcriptional level. Although the Ethylene Response Factor (ERF) gene family is one of the most well-studied stress-responsive gene families in plants, their promoter regions have received little attention. In this study, we investigated the expression patterns driven by the soybean (Glycine max) GmERF3 promoter and its cis-acting elements in soybean and tobacco. Transcriptomic data revealed that the native GmERF3 gene was differentially expressed in organs and tissues of plants. In transgenic soybeans containing a 1.3 kb GmERF3 promoter fused to the green fluorescent protein (gfp) gene, organ- and tissue-specificity was observed in untreated plants while mechanical wounding led to induction of GFP expression. Further in silico and in planta analyses of the GmERF3 promoter sequence in soybean revealed different cis-acting elements, including a novel cis-acting element, which contributed to increased expression, 1-2 days after mechanical wounding. We have named this DNA motif the wound-induced and delayed expression element (GGATTCAAGTTTAACC). A synthetic promoter containing a tetrameric repeat of this element showed high but late wound-induced GFP expression in leaves of transgenic tobacco. Our study expands the toolbox of inducible promoters and promoter elements for potential use in basic and applied research.

OsIAA6, a member of the rice Aux/IAA gene family, is involved in drought tolerance and tiller outgrowth

Auxin signaling is a fundamental part of many plant growth processes and stress responses and operates through Aux/IAA protein degradation and the transmission of the signal via auxin response factors (ARFs). A total of 31 Aux/IAA genes have been identified in rice (Oryza sativa), some of which are induced by drought stress. However, the mechanistic link between Aux/IAA expression and drought responses is not well understood. In this study we found that the rice Aux/IAA gene OsIAA6 is highly induced by drought stress and that its overexpression in transgenic rice improved drought tolerance, likely via the regulation of auxin biosynthesis genes. We observed that OsIAA6 was specifically expressed in the axillary meristem of the basal stem, which is the tissue that gives rise to tillers. A knock-down mutant of OsIAA6 showed abnormal tiller outgrowth, apparently due to the regulation of the auxin transporter OsPIN1 and the rice tillering inhibitor OsTB1. Our results confirm that the OsIAA6 gene is involved in drought stress responses and the control of tiller outgrowth.

The activities of four constitutively expressed promoters in single-copy transgenic rice plants for two homozygous generations

We have characterized four novel constitutive promoters ARP1, H3F3, HSP and H2BF3 that are active in all tissues/stages of transgenic plants and stable over two homozygous generations. Gene promoters that are active and stable over several generations in transgenic plants are valuable tools for plant research and biotechnology. In this study, we characterized four putative constitutive promoters (ARP1, H3F3, HSP and H2BF3) in transgenic rice plants. Promoter regions were fused to the green fluorescence protein (GFP) reporter gene and transformed into rice. Single-copy transgenic lines were then selected and promoter activity was analyzed in various organs and tissues of two successive homozygous generations. All four promoters showed a broad expression profile in most tissues and developmental stages, and indeed the expression of the ARP1 and H3F3 promoters was even greater than that of the PGD1 promoter, a previously described constitutive promoter that has been used in transgenic rice. This observation was based on expression levels in leaves, roots, dry seeds and flowers in both the T2 and T3 generations. Each promoter exhibited comparable levels of activity over two homozygous generations with no sign of transgene silencing, which is an important characteristic of promoters to be used in crop biotechnology applications. These promoters therefore have considerable potential value for the stable and constitutive expression of transgenes in monocotyledonous crops.

Plant promoters: an approach of structure and function

With current advances in genomics, several technological processes have been generated, resulting in improvement in different segments of molecular research involving prokaryotic and eukaryotic systems. A widely used contribution is the identification of new genes and their functions, which has led to the elucidation of several issues concerning cell regulation and interactions. For this, increase in the knowledge generated from the identification of promoters becomes considerably relevant, especially considering that to generate new technological processes, such as genetically modified organisms, the availability of promoters that regulate the expression of new genes is still limited. Considering that this issue is essential for biotechnologists, this paper presents an updated review of promoters, from their structure to expression, and focuses on the knowledge already available in eukaryotic systems. Information on current promoters and methodologies available for studying their expression are also reported.

Identification and validation of promoters and cis-acting regulatory elements

Studies of promoters that largely regulate gene expression at the transcriptional level are crucial for improving our basic understanding of gene regulation and will expand the toolbox of available promoters for use in plant biotechnology. In this review, we present a comprehensive analysis of promoters and their underlying mechanisms in transcriptional regulation, including epigenetic marks and chromatin-based regulation. Large-scale prediction of promoter sequences and their contributing cis-acting elements has become routine due to recent advances in transcriptomic technologies and genome sequencing of several plants. However, predicted regulatory sequences may or may not be functional and demonstration of the contribution of the element to promoter activity is essential for confirmation of regulatory sequences. Synthetic promoters and introns provide useful approaches for functional validation of promoter sequences. The development and improvement of gene expression tools for rapid, efficient, predictable, and high-throughput analysis of promoter components will be critical for confirmation of the functional regulatory element sequences identified through transcriptomic and genomic analyses.

Genetic engineering of crops: a ray of hope for enhanced food security

Crop improvement has been a basic and essential chase since organized cultivation of crops began thousands of years ago. Abiotic stresses as a whole are regarded as the crucial factors restricting the plant species to reach their full genetic potential to deliver desired productivity. The changing global climatic conditions are making them worse and pointing toward food insecurity. Agriculture biotechnology or genetic engineering has allowed us to look into and understand the complex nature of abiotic stresses and measures to improve the crop productivity under adverse conditions. Various candidate genes have been identified and transformed in model plants as well as agriculturally important crop plants to develop abiotic stress-tolerant plants for crop improvement. The views presented here are an attempt toward realizing the potential of genetic engineering for improving crops to better tolerate abiotic stresses in the era of climate change, which is now essential for global food security. There is great urgency in speeding up crop improvement programs that can use modern biotechnological tools in addition to current breeding practices for providing enhanced food security.

Enhanced transgene expression in rice following selection controlled by weak promoters

BACKGROUND

Techniques that enable high levels of transgene expression in plants are attractive for the commercial production of plant-made recombinant pharmaceutical proteins or other gene transfer related strategies. The conventional way to increase the yield of desired transgenic products is to use strong promoters to control the expression of the transgene. Although many such promoters have been identified and characterized, the increase obtainable from a single promoter is ultimately limited to a certain extent.

RESULTS

In this study, we report a method to magnify the effect of a single promoter by using a weak promoter-based selection system in transgenic rice. tCUP1, a fragment derived from the tobacco cryptic promoter (tCUP), was tested for its activity in rice by fusion to both a β-glucuronidase (GUS) reporter and a hygromycin phosphotransferase (HPT) selectable marker. The tCUP1 promoter allowed the recovery of transformed rice plants and conferred tissue specific expression of the GUS reporter, but was much weaker than the CaMV 35S promoter in driving a selectable marker for growth of resistant calli. However, in the resistant calli and regenerated transgenic plants selected by the use of tCUP1, the constitutive expression of green fluorescent protein (GFP) was dramatically increased as a result of the additive effect of multiple T-DNA insertions. The correlation between attenuated selection by a weak promoter and elevation of copy number and foreign gene expression was confirmed by using another relatively weak promoter from nopaline synthase (Nos).

CONCLUSIONS

The use of weak promoter derived selectable markers leads to a high T-DNA copy number and then greatly increases the expression of the foreign gene. The method described here provides an effective approach to robustly enhance the expression of heterogenous transgenes through copy number manipulation in rice.

OsNAC5 overexpression enlarges root diameter in rice plants leading to enhanced drought tolerance and increased grain yield in the field

Drought conditions are among the most serious challenges to crop production worldwide. Here, we report the results of field evaluations of transgenic rice plants overexpressing OsNAC5, under the control of either the root-specific (RCc3) or constitutive (GOS2) promoters. Field evaluations over three growing seasons revealed that the grain yield of the RCc3:OsNAC5 and GOS2:OsNAC5 plants were increased by 9%-23% and 9%-26% under normal conditions, respectively. Under drought conditions, however, RCc3:OsNAC5 plants showed a significantly higher grain yield of 22%-63%, whilst the GOS2:OsNAC5 plants showed a reduced or similar yield to the nontransgenic (NT) controls. Both the RCc3:OsNAC5 and GOS2:OsNAC5 plants were found to have larger roots due to an enlarged stele and aerenchyma at flowering stage. Cell numbers per cortex layer and stele of developing roots were higher in both transgenic plants than NT controls, contributing to the increase in root diameter. The root diameter was enlarged to a greater extent in the RCc3:OsNAC5, suggesting the importance of this phenotype for enhanced drought tolerance. Microarray experiments identified 25 up-regulated genes by more than three-fold (P < 0.01) in the roots of both transgenic lines. Also identified were 19 and 18 up-regulated genes that are specific to the RCc3:OsNAC5 and GOS2:OsNAC5 roots, respectively. Of the genes specifically up-regulated in the RCc3:OsNAC5 roots, GLP, PDX, MERI5 and O-methyltransferase were implicated in root growth and development. Our present findings demonstrate that the root-specific overexpression of OsNAC5 enlarges roots significantly and thereby enhances drought tolerance and grain yield under field conditions.