MusaSAP1, a A20/AN1 zinc finger gene from banana functions as a positive regulator in different stress responses

Heterologous overexpression of the Suaeda glauca stress-associated protein (SAP) family genes enhanced salt tolerance in Arabidopsis transgenic lines

Stress-associated proteins (SAPs), characterized by zinc finger domains, play a crucial role in regulating plant responses to various stresses. These proteins modulate stress-related gene expression and are integral to enhancing plant immunity, development, cell proliferation, and hormone regulation. In this study, we conducted a genome-wide analysis of the SAP gene family in Suaeda glauca (S. glauca), identifying 15 SAP genes encoding A20/AN1 zinc finger proteins. Functional analyses of three candidate genes under salinity stress were performed, examining phenotypic and physiological responses to better understand their role in stress tolerance. Sequence alignment, conserved domain analysis, and gene structure analysis revealed high conservation among S. glauca SAPs. Phylogenetic analysis identified two major groups within the gene family, providing insights into their evolutionary relationships. Transcription profiling analysis demonstrated significant expression of most SAP genes in response to salt stress, with qPCR validation confirming the upregulation of specific genes. Notably, transgenic Arabidopsis lines heterologously overexpressing the candidate genes SgSAP4, SgSAP5, and SgSAP7 demonstrated enhanced tolerance to salinity stress. This was evident from improved seed germination, root elongation, and reduced levels of stress markers, including malondialdehyde and free proline, compared to wild-type plants. These findings highlight the potential of these SAP genes in breeding programs aimed at improving salinity tolerance in crops.

Transcriptome sequence reveal the roles of MaGME777 and MabHLH770 in drought tolerance in Musa acuminata

Banana, a globally cultivated fruit, faces significant constraints in distribution and sustainable production due to drought stress. This study investigated drought tolerance in Cavendish bananas using RNA-seq time-course analysis and molecular biology experiments. Plants were subjected to dehydration treatments, and physiological indicators such as electrolyte leakage, proline content, malonaldehyde, peroxidase activity, and hydrogen peroxide content were assessed. RNA-Seq and qRT-PCR were used to analyze transcriptional changes under drought. Weighted gene co-expression network (WGCNA) analysis identified thousands of differentially expressed genes (DEGs) at different time points, with a core set of 2660 DEGs consistently identified. KEGG enrichment analysis revealed MaGME777, a glycolysis/gluconeogenesis gene, as a potential drought resistance regulator. Virus-mediated gene silencing (VIGS) of MaGME777 reduced drought tolerance in bananas. Yeast one-hybrid (Y1H) and luciferase reporter assays demonstrated that the transcription factor MabHLH770 directly binds and activates the MaGME777 promoter. VIGS downregulation of MabHLH770 also reduced drought tolerance. In conclusion, this study revealed that MabHLH770 is a positive regulator of drought stress, by targeting MaGME777 promoter and activating their expression to enhance drought tolerance. These findings provide a foundation for developing drought-resistant banana cultivars through molecular breeding approaches.

Shaping the future of bananas: advancing genetic trait regulation and breeding in the postgenomics era

Bananas (Musa spp.) are among the top-produced food crops, serving as a primary source of food for millions of people. Cultivated bananas originated primarily from the wild diploid species Musa acuminata (A genome) and Musa balbisiana (B genome) through intra- and interspecific hybridization and selections via somatic variation. Following the publication of complete A- and B-genome sequences, prospects for complementary studies on S- and T-genome traits, key gene identification for yield, ripening, quality, and stress resistance, and advances in molecular breeding have significantly expanded. In this review, latest research progress on banana A, B, S, and T genomes is briefly summarized, highlighting key advances in banana cytoplasmic inheritance, flower and fruit development, sterility, and parthenocarpy, postharvest ripening and quality regulation, and biotic and abiotic stress resistance associated with desirable economic traits. We provide updates on transgenic, gene editing, and molecular breeding. We also explore future directions for banana breeding and genetic improvement.

Research progress on plant stress-associated protein (SAP) family: Master regulators to deal with environmental stresses

Every year, unfavorable environmental factors significantly affect crop productivity and threaten food security. Plants are sessile; they cannot move to escape unfavorable environmental conditions, and therefore, they activate a variety of defense pathways. Among them are processes regulated by stress-associated proteins (SAPs). SAPs have a specific zinc finger domain (A20) at the N-terminus and either AN1 or C2H2 at the C-terminus. SAP proteins are involved in many biological processes and in response to various abiotic or biotic constraints. Most SAPs play a role in conferring transgenic stress resistance and are stress-inducible. The emerging field of SAPs in abiotic or biotic stress response regulation has attracted the attention of researchers. Although SAPs interact with various proteins to perform their functions, the exact mechanisms of these interactions remain incompletely understood. This review aims to provide a comprehensive understanding of SAPs, covering their diversity, structure, expression, and subcellular localization. SAPs play a pivotal role in enabling crosstalk between abiotic and biotic stress signaling pathways, making them essential for developing stress-tolerant crops without yield penalties. Collectively, understanding the complex regulation of SAPs in stress responses can contribute to enhancing tolerance against various environmental stresses through several techniques such as transgenesis, classical breeding, or gene editing.

AoSAP8-P encoding A20 and/or AN1 type zinc finger protein in asparagus officinalis L. Improving stress tolerance in transgenic Nicotiana sylvestris

The full length CDS of an A20 and AN1 type zinc finger gene (named AoSAP8-P), located nearby the male specific Y chromosome (MSY) region of Asparagus officinalis (garden asparagus) was amplified by RT-PCR from purple passion. This gene, predicted as the stress associated protein (SAPs) gene families, encodes 172 amino acids with multiple cis elements including light, stress response box, MYB and ERF binding sites on its promoter. To analyze its function, the gene expression of different organs in different asparagus gender were analyzed and the overexpressed transgenic Nicotiana sylvestris lines were generated. The results showed the gene was highly expressed in both flower and root of male garden asparagus; the germination rate of seeds of the T2 transgenic lines (T2-5-4 and T2-7-1) under the stress conditions of 125 mM NaCl and 150 mM mannitol were significantly higher than the wild type (WT) respectively. When the potted T2-5-4, T2-7-1 lines and WT were subjected to drought stress for 24 days and the leaf discs immerged into 20 % PEG6000 and 300 mM NaCl solution for 48 h respectively, the T2-5-4 and T2-7-1 with AoSAP8-P expression showed stronger drought, salt and osmotic stress tolerance. When compared, the effects of AoSAP8-P overexpression on productive development showed that the flowering time of transgenic lines, were ∼ 9 day earlier with larger but fewer pollens than its WT counterparts. However, there were no significant differences in anthers, stigmas and pollen viability between the transgenic lines and WT. Our results suggested that, the AoSAP8-P gene plays a role in improving the stress resistance and shortening seeds generation time for perianal survival during the growth and development of garden asparagus.

MaDREB1F confers cold and drought stress resistance through common regulation of hormone synthesis and protectant metabolite contents in banana

Adverse environmental factors severely affect crop productivity. Improving crop resistance to multiple stressors is an important breeding goal. Although CBFs/DREB1s extensively participate in plant resistance to abiotic stress, the common mechanism underlying CBFs/DREB1s that mediate resistance to multiple stressors remains unclear. Here, we show the common mechanism for MaDREB1F conferring cold and drought stress resistance in banana. MaDREB1F encodes a dehydration-responsive element binding protein (DREB) transcription factor with nuclear localization and transcriptional activity. MaDREB1F expression is significantly induced after cold, osmotic, and salt treatments. MaDREB1F overexpression increases banana resistance to cold and drought stress by common modulation of the protectant metabolite levels of soluble sugar and proline, activating the antioxidant system, and promoting jasmonate and ethylene syntheses. Transcriptomic analysis shows that MaDREB1F activates or alleviates the repression of jasmonate and ethylene biosynthetic genes under cold and drought conditions. Moreover, MaDREB1F directly activates the promoter activities of MaAOC4 and MaACO20 for jasmonate and ethylene syntheses, respectively, under cold and drought conditions. MaDREB1F also targets the MaERF11 promoter to activate MaACO20 expression for ethylene synthesis under drought stress. Together, our findings offer new insight into the common mechanism underlying CBF/DREB1-mediated cold and drought stress resistance, which has substantial implications for engineering cold- and drought-tolerant crops.

OsSAP6 Positively Regulates Soda Saline-Alkaline Stress Tolerance in Rice

BACKGROUND

Soil salinization is a worldwide environmental problem, especially in the arid and semiarid regions of northeastern China, which are heavily affected by soda saline-alkaline stress. At present, there is an urgent need to improve the soda saline-alkaline stress tolerance of rice.

RESULTS

Stress-associated proteins are involved in regulating the abiotic stresses in plants. There are 18 members of the rice stress-associated protein (OsSAP) gene family. In this study, the expression levels of OsSAP6 in leaves and roots were upregulated with increasing NaHCO₃ stress duration. OsSAP6 was located in nucleus and cytoplasm. The bud length and total root length of OsSAP6 overexpression rice were significantly longer than those of Lj11 (Oryza sativa longjing11) during germination stage, and the survival rates, plant height and malondialdehyde content at the seedling stage showed tolerance growth of saline-alkaline stress. The expression of OsCu/Zn-SOD, OsAPX2, and OsCAT1 in transgenic lines was increased significantly under SAE (soda saline-alkali soil eluent) stress. OsSAP6 interacts with OsPK5 according to yeast two-hybrid screening and luciferase complementation experiments. The expression of OsPK5 increased under NaHCO₃ and H₂O₂ stress, and the overexpression of OsPK5 in rice improved soda saline-alkaline tolerance.

CONCLUSION

Overexpression of OsSAP6 in rice significantly enhanced saline-alkaline tolerance compared with the wild type. It is speculated that OsSAP6 responds to soda salinity stress and interacts with OsPK5 to positively regulate soda saline-alkaline tolerance through ROS homeostasis. This study revealed the features of OsSAP6 involved in response to soda saline-alkaline stress and the interaction with OsPK5, which provided resources for breeding aimed at improving the soda saline-alkaline stress tolerance of rice.

Comprehensive Identification and Functional Analysis of Stress-Associated Protein (SAP) Genes in Osmotic Stress in Maize

Stress-associated proteins (SAPs) are a kind of zinc finger protein with an A20/AN1 domain and contribute to plants' adaption to various abiotic and biological stimuli. However, little is known about the SAP genes in maize (Zea mays L.). In the present study, the SAP genes were identified from the maize genome. Subsequently, the protein properties, gene structure and duplication, chromosomal location, and cis-acting elements were analyzed by bioinformatic methods. Finally, their expression profiles under osmotic stresses, including drought and salinity, as well as ABA, and overexpression in Saccharomyces cerevisiae W303a cells, were performed to uncover the potential function. The results showed that a total of 10 SAP genes were identified and named ZmSAP1 to ZmSAP10 in maize, which was unevenly distributed on six of the ten maize chromosomes. The ZmSAP1, ZmSAP4, ZmSAP5, ZmSAP6, ZmSAP7, ZmSAP8 and ZmSAP10 had an A20 domain at N terminus and AN1 domain at C terminus, respectively. Only ZmSAP2 possessed a single AN1 domain at the N terminus. ZmSAP3 and ZmSAP9 both contained two AN1 domains without an A20 domain. Most ZmSAP genes lost introns and had abundant stress- and hormone-responsive cis-elements in their promoter region. The results of quantitative real-time PCR showed that all ZmSAP genes were regulated by drought and saline stresses, as well as ABA induction. Moreover, heterologous expression of ZmSAP2 and ZmSAP7 significantly improved the saline tolerance of yeast cells. The study provides insights into further underlying the function of ZmSAPs in regulating stress response in maize.

Genome-Wide Identification of the A20/AN1 Zinc Finger Protein Family Genes in Ipomoea batatas and Its Two Relatives and Function Analysis of IbSAP16 in Salinity Tolerance

Stress-associated protein (SAP) genes—encoding A20/AN1 zinc-finger domain-containing proteins—play pivotal roles in regulating stress responses, growth, and development in plants. They are considered suitable candidates to improve abiotic stress tolerance in plants. However, the SAP gene family in sweetpotato (Ipomoea batatas) and its relatives is yet to be investigated. In this study, 20 SAPs in sweetpotato, and 23 and 26 SAPs in its wild diploid relatives Ipomoea triloba and Ipomoea trifida were identified. The chromosome locations, gene structures, protein physiological properties, conserved domains, and phylogenetic relationships of these SAPs were analyzed systematically. Binding motif analysis of IbSAPs indicated that hormone and stress responsive cis-acting elements were distributed in their promoters. RT-qPCR or RNA-seq data revealed that the expression patterns of IbSAP, ItbSAP, and ItfSAP genes varied in different organs and responded to salinity, drought, or ABA (abscisic acid) treatments differently. Moreover, we found that IbSAP16 driven by the 35 S promoter conferred salinity tolerance in transgenic Arabidopsis. These results provided a genome-wide characterization of SAP genes in sweetpotato and its two relatives and suggested that IbSAP16 is involved in salinity stress responses. Our research laid the groundwork for studying SAP-mediated stress response mechanisms in sweetpotato.

Genome-wide in silico identification and characterization of the stress associated protein (SAP) gene family encoding A20/AN1 zinc-finger proteins in potato (Solanum tuberosum L.)

Stress associated proteins (SAPs) in plants have a key role in providing tolerance to multiple abiotic stresses. SAP gene family in Solanum tuberosum has not been fully studied before. This study identified 17 StSAP genes in S. tuberosum which code for A20/AN1 zinc-finger proteins. All the genes were distributed on ten different chromosomes and six segmental duplication events were identified. The SAPs in S. tuberosum and its orthologs in Arabidopsis thaliana were classified into six groups through the phylogenetic analysis. Introns across StSAP genes were identified in four genes. The promotor study of the StSAP genes showed different hormone and stress-related cis-elements that could potentially have a role in environmental stress response. The expression of StSAP genes in response to heat, mannitol, and salt were analyzed through in silico transcriptomic analysis. This study could potentially help in further understanding the functions of SAP genes in S. tuberosum.

Genome-Wide Analyses of Tea Plant Stress-Associated Proteins (SAPs) Reveal the Role of CsSAP12 in Increased Drought Tolerance in Transgenic Tomatoes

Plant stress-associated proteins (SAPs) contain A20/AN1 zinc finger domains and are involved in plant response to abiotic stresses. In this study, we aimed to explore the biological function of tea plant CsSAPs. A total of 14 CsSAP genes were identified in the tea plant genome using a reference genome database (Camellia sinensis var. sinensis). The CsSAPs were divided into the following two groups: Group I, containing one AN1 domain and/or one A20 domain; and Group II, containing two AN1 domains and/or two C2H2 domains. The sequence alignments and conserved domains analysis indicated that the CsSAPs were highly structurally conserved in terms of amino acid sequence and protein structure. The CsSAPs showed different transcript levels in spatio-temporal expression and in response to cold and drought stress in tea plants. Furthermore, the expression of CsSAP12 was considerably upregulated under drought stress. The overexpression of CsSAP12 in transgenic tomatoes showed increased tolerance to drought stress compared with the wild type. Altogether, the results showed that CsSAP12 might be involved in drought stress. Thus, CsSAP12 might be a target gene in genetic engineering to improve drought tolerance in tea plants.

A stress-associated protein OsSAP8 modulates gibberellic acid biosynthesis by reducing the promotive effect of transcription factor OsbZIP58 on OsKO2

Gibberellic acid (GA) is a vital phytohormone for plant growth and development. GA biosynthesis is a complex pathway regulated by various transcription factors. Here we report a stress-associated protein 8 (OsSAP8), negatively involved in GA biosynthesis. Overexpression of OsSAP8 in rice resulted in a semi-dwarfism phenotype and reduced endogenous GA3 content. In contrast, an OsSAP8 knockout mutant exhibited higher endogenous GA3 content and slightly increased plant height. Sub-cellular localization analysis of OsSAP8 showed that it could enter the nucleus. Based on electrophoretic mobility shift assay and yeast one hybrid experiments, OsSAP8 was found to bind to the cis-acting regulatory element GADOWNAT of ent-kaurene oxidases (KO2, KO3, KO5). The results from dual-luciferase reporter assays showed that OsSAP8 does not activate LUC reporter gene expression. However, it could interact with basic leucine zipper 58 (OsbZIP58), which has strong transcriptional activation potential on OsKO2. Moreover, the interaction between OsSAP8, rice lesion simulating disease 1-like 1 (OsLOL1), and OsbZIP58 could reduce the promotive effect of transcription factor OsbZIP58 on OsKO2. These results provide some new insights on the regulation of GA biosynthesis in rice.

Expression of Specific Alleles of Zinc-Finger Transcription Factors, HvSAP8 and HvSAP16, and Corresponding SNP Markers, Are Associated with Drought Tolerance in Barley Populations

Two genes, HvSAP8 and HvSAP16, encoding Zinc-finger proteins, were identified earlier as active in barley plants. Based on bioinformatics and sequencing analysis, six SNPs were found in the promoter regions of HvSAP8 and one in HvSAP16, among parents of two barley segregating populations, Granal × Baisheshek and Natali × Auksiniai-2. ASQ and Amplifluor markers were developed for HvSAP8 and HvSAP16, one SNP in each gene, and in each of two populations, showing simple Mendelian segregation. Plants of F6 selected breeding lines and parents were evaluated in a soil-based drought screen, revealing differential expression of HvSAP8 and HvSAP16 corresponding with the stress. After almost doubling expression during the early stages of stress, HvSAP8 returned to pre-stress level or was strongly down-regulated in plants with Granal or Baisheshek genotypes, respectively. For HvSAP16 under drought conditions, a high expression level was followed by either a return to original levels or strong down-regulation in plants with Natali or Auksiniai-2 genotypes, respectively. Grain yield in the same breeding lines and parents grown under moderate drought was strongly associated with their HvSAP8 and HvSAP16 genotypes. Additionally, Granal and Natali genotypes with specific alleles at HvSAP8 and HvSAP16 were associated with improved performance under drought via higher 1000 grain weight and more shoots per plant, respectively.

The regulation of DKGA2ox1 and miR171f_3 in scion dwarfing with Diospyros kaki Thunb. cv. 'Nan-tong-xiao-fang-shi' as interstocks

High-throughput sequencing and yeast one and two-hybrid library screening reveal that DKGA2ox1 and miR171f_3 are involved in the regulation of scion dwarfing with 'Nan-tong-xiao-fang-shi' as interstocks. Diospyros kaki Thunb. cv. Nan-tong-xiao-fang-shi ('Nan-tong-xiao-fang-shi') interstocks play a critical role in the scion dwarfing. However, the understanding of the molecular signaling pathways that regulate the scion dwarfing with 'Nan-tong-xiao-fang-shi' as interstocks remain unclear. In this work, the regulatory network in the scion dwarfing with 'Nan-tong-xiao-fang-shi' as interstocks was identified. Using a yeast one-hybrid library screening, luciferase activity analysis, luciferase complementation imaging assays and GFP signal detection, a SPL transcription factor named Diospyros kaki SPL (DKSPL), potentially functioning as a transcriptional activator of the Diospyros kaki GA2ox1 (DKGA2ox1) gene, was identified as a key stimulating factor in the persimmon growth and development. The DKSPL was found in the nucleus, and might play a role in the transcriptional regulation system. A microRNA named miR171f_3 was identified, which might act as a negative regulator of Diospyros kaki SCR (DKSCR) in persimmon. The interactions between DKSCR and seven proteins were experimentally validated with a yeast two-hybrid library screening. Compared to the non-grafted wildtype persimmon, the tissue section of graft union healed well due to the increased expression of cinnamyl-alcohol dehydrogenase. These results indicate that DKGA2ox1 and miR171f_3 may co-promote the scion dwarfing by plant hormone signal transduction pathways.

Comprehensive analysis of the stress associated protein (SAP) gene family in Tamarix hispida and the function of ThSAP6 in salt tolerance

Stress associated proteins (SAPs), a class of A20/AN1 zinc finger domain-containing proteins, are involved in a variety of biotic and abiotic stress responses in plants. However, little is known about the SAP gene family and their functions in Tamarix hispida. In this study, we isolated and characterized 11 SAPs from T. hispida. The expression patterns of ThSAPs were analyzed under various stresses (salt and drought) and phytohormone treatment (SA, ABA and MeJA) using real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR). Most ThSAPs exhibited transcriptional responses to abiotic stresses and phytohormones. Among these ThSAPs, ThSAP6 was significantly induced by salt stress. Gain-and loss-of-function analyses revealed that ThSAP6 was a positive regulator of salt stress response. Overexpression of ThSAP6 in T. hispida increased antioxidant enzymes activity and proline content and decreased reactive oxygen species (ROS) accumulation and cell membrane damage under salt stress, while the opposite physiological changes were observed in ThSAP6-RNAi (RNA interference) lines. This study provides a comprehensive description of the SAP gene family in T. hispida, and demonstrates that ThSAP6 is a potential candidate for biotechnological approaches to improve salt tolerance in plants.

Genomic characterization and expression profiles of stress-associated proteins (SAPs) in castor bean (Ricinus communis)

Stress-associated proteins (SAPs) are known as response factors to multiple abiotic and biotic stresses in plants. However, the potential physiological and molecular functions of SAPs remain largely unclear. Castor bean (Ricinus communis L.) is one of the most economically valuable non-edible woody oilseed crops, able to be widely cultivated in marginal lands worldwide because of its broad adaptive capacity to soil and climate conditions. Whether SAPs in castor bean plays a key role in adapting diverse soil conditions and stresses remains unknown. In this study, we used the castor bean genome to identify and characterize nine castor bean SAP genes (RcSAP). Structural analysis showed that castor bean SAP gene structures and functional domain types vary greatly, differing in intron number, protein sequence, and functional domain type. Notably, the AN1-C2H2-C2H2 zinc finger domain within RcSAP9 has not been often observed in other plant families. High throughput RNA-seq data showed that castor bean SAP gene profiles varied among different tissues. In addition, castor bean SAP gene expression varied in response to different stresses, including salt, drought, heat, cold and ABA and MeJA, suggesting that the transcriptional regulation of castor bean SAP genes might operate independently of each other, and at least partially independent from ABA and MeJA signal pathways. Cis-element analyses for each castor bean SAP gene showed that no common cis-elements are shared across the nine castor bean SAP genes. Castor bean SAPs were localized to different regions of cells, including the cytoplasm, nucleus, and cytomembrane. This study provides a comprehensive profile of castor bean SAP genes that advances our understanding of their potential physiological and molecular functions in regulating growth and development and their responses to different abiotic stresses.

Cloning and Characterization of TaSAP7-A, a Member of the Stress-Associated Protein Family in Common Wheat

Stress association proteins (SAPs) are A20/AN1 zinc-finger domain proteins, which play important roles in plant adaptation to abiotic stress and plant development. The functions of SAPs in some plants were reported, but little is known about it in wheat (Triticum aestivum L.). In this study, we characterized a novel 2AN1-type stress association protein gene TaSAP7-A, which was mapped to chromosome 5A in wheat. Subcellular localization indicated that TaSAP7-A was distributed in the nucleus and cytoplasm. Unlike previously known A20/AN1-type SAP genes, TaSAP7-A was negatively regulated to abiotic stress tolerance. Overexpressing TaSAP7-A Arabidopsis lines were hypersensitive to ABA, osmotic and salt stress at germination stage and post-germination stage. Overexpression of TaSAP7-A Arabidopsis plants accelerated the detached leaves' chlorophyll degradation. Association analysis of TaSAP7-A haplotypes and agronomic traits showed that Hap-5A-2 was significantly associated with higher chlorophyll content at jointing stage and grain-filling stage. These results jointly revealed that TaSAP7-A is related to the chlorophyll content in the leaves of Arabidopsis and wheat. Both in vivo and in vitro experiments demonstrated that TaSAP7-A interacted with TaS10B, which was the component of regulatory subunit in 26S proteasome. In general, TaSAP7-A was a regulator of chlorophyll content, and favorable haplotypes should be helpful for improving plant chlorophyll content and grain yield of wheat.

Using Genetic Engineering Techniques to Develop Banana Cultivars With Fusarium Wilt Resistance and Ideal Plant Architecture

Bananas (Musa spp.) are an important fruit crop worldwide. The fungus Fusarium oxysporum f. sp. cubense (Foc), which causes Fusarium wilt, is widely regarded as one of the most damaging plant diseases. Fusarium wilt has previously devastated global banana production and continues to do so today. In addition, due to the current use of high-density banana plantations, desirable banana varieties with ideal plant architecture (IPA) possess high lodging resistance, optimum photosynthesis, and efficient water absorption. These properties may help to increase banana production. Genetic engineering is useful for the development of banana varieties with Foc resistance and ideal plant architecture due to the sterility of most cultivars. However, the sustained immune response brought about by genetic engineering is always accompanied by yield reductions. To resolve this problem, we should perform functional genetic studies of the Musa genome, in conjunction with genome editing experiments, to unravel the molecular mechanisms underlying the immune response and the formation of plant architecture in the banana. Further explorations of the genes associated with Foc resistance and ideal architecture might lead to the development of banana varieties with both ideal architecture and pathogen super-resistance. Such varieties will help the banana to remain a staple food worldwide.

Identification and characterization of differentially expressed genes in the rice root following exogenous application of spermidine during salt stress

Salinity is a major limiting factor in crop production. Exogenous spermidine (spd) effectively ameliorates salt injury, though the underlying molecular mechanism is poorly understood. We have used a suppression subtractive hybridization method to construct a cDNA library that has identified up-regulated genes from rice root under the treatment of spd and salt. Total 175 high-quality ESTs of about 100-500 bp in length with an average size of 200 bp are isolated, clustered and assembled into a collection of 62 unigenes. Gene ontology analysis using the KEGG pathway annotation database has classified the unigenes into 5 main functional categories and 13 subcategories. The transcripts abundance has been validated using Real-Time PCR. We have observed seven different types of post-translational modifications in the DEPs. 44 transmembrane helixes are predicted in 6 DEPs. This above information can be used as first-hand data for dissecting the administrative role of spd during salinity.

An aquaporin gene MaPIP2-7 is involved in tolerance to drought, cold and salt stresses in transgenic banana (Musa acuminata L.)

Aquaporins (AQPs) transport water and other small molecules; however, their precise role in abiotic stress responses is not fully understood. In this study, we cloned and characterized the PIP2 group AQP gene, MaPIP2-7, in banana. MaPIP2-7 expression was upregulated after osmotic (mannitol), cold, and salt treatments. Overexpression of MaPIP2-7 in banana improved tolerance to multiple stresses such as drought, cold, and salt. MaPIP2-7 transgenic plants showed lower levels of malondialdehyde (MDA) and ion leakage (IL), but higher contents of chlorophyll, proline, soluble sugar, and abscisic acid (ABA) compared with wild type (WT) plants under stress and recovery conditions. Additionally, MaPIP2-7 overexpression decreased cellular contents of Na⁺ and K⁺ under salt and recovery conditions, and produced an elevated K⁺/Na⁺ ratio under recovery conditions. Finally, ABA biosynthetic and responsive genes exhibited higher expression levels in transgenic lines relative to WT under stress conditions. Taken together, our results demonstrate that MaPIP2-7 confers tolerance to drought, cold, and salt stresses by maintaining osmotic balance, reducing membrane injury, and improving ABA levels.

A Stress-Associated Protein, PtSAP13, From Populus trichocarpa Provides Tolerance to Salt Stress

The growth and production of poplars are usually affected by unfavorable environmental conditions such as soil salinization. Thus, enhancing salt tolerance of poplars will promote their better adaptation to environmental stresses and improve their biomass production. Stress-associated proteins (SAPs) are a novel class of A20/AN1 zinc finger proteins that have been shown to confer plants' tolerance to multiple abiotic stresses. However, the precise functions of SAP genes in poplars are still largely unknown. Here, the expression profiles of Populus trichocarpa SAPs in response to salt stress revealed that PtSAP13 with two AN1 domains was up-regulated dramatically during salt treatment. The β-glucuronidase (GUS) staining showed that PtSAP13 was accumulated dominantly in leaf and root, and the GUS signal was increased under salt condition. The Arabidopsis transgenic plants overexpressing PtSAP13 exhibited higher seed germination and better growth than wild-type (WT) plants under salt stress, demonstrating that overexpression of PtSAP13 increased salt tolerance. Higher activities of antioxidant enzymes were found in PtSAP13-overexpressing plants than in WT plants under salt stress. Transcriptome analysis revealed that some stress-related genes, including Glutathione peroxidase 8, NADP-malic enzyme 2, Response to ABA and Salt 1, WRKYs, Glutathione S-Transferase, and MYBs, were induced by salt in transgenic plants. Moreover, the pathways of flavonoid biosynthesis and metabolic processes, regulation of response to stress, response to ethylene, dioxygenase activity, glucosyltransferase activity, monooxygenase activity, and oxidoreductase activity were specially enriched in transgenic plants under salt condition. Taken together, our results demonstrate that PtSAP13 enhances salt tolerance through up-regulating the expression of stress-related genes and mediating multiple biological pathways.

Overexpression of native Musa-miR397 enhances plant biomass without compromising abiotic stress tolerance in banana

Plant micro RNAs (miRNAs) control growth, development and stress tolerance but are comparatively unexplored in banana, whose cultivation is threatened by abiotic stress and nutrient deficiencies. In this study, a native Musa-miR397 precursor harboring 11 copper-responsive GTAC motifs in its promoter element was identified from banana genome. Musa-miR397 was significantly upregulated (8-10) fold in banana roots and leaves under copper deficiency, correlating with expression of root copper deficiency marker genes such as Musa-COPT and Musa-FRO2. Correspondingly, target laccases were significantly downregulated (>-2 fold), indicating miRNA-mediated silencing for Cu salvaging. No significant expression changes in the miR397-laccase module were observed under iron stress. Musa-miR397 was also significantly upregulated (>2 fold) under ABA, MV and heat treatments but downregulated under NaCl stress, indicating universal stress-responsiveness. Further, Musa-miR397 overexpression in banana significantly increased plant growth by 2-3 fold compared with wild-type but did not compromise tolerance towards Cu deficiency and NaCl stress. RNA-seq of transgenic and wild type plants revealed modulation in expression of 71 genes related to diverse aspects of growth and development, collectively promoting enhanced biomass. Summing up, our results not only portray Musa-miR397 as a candidate for enhancing plant biomass but also highlight it at the crossroads of growth-defense trade-offs.

Functional domain analysis of LmSAP protein reveals the crucial role of the zinc-finger A20 domain in abiotic stress tolerance

Stress-associated proteins (SAPs), such as A20/AN1 zinc-finger domain-containing proteins, have emerged as a novel class of proteins involved in abiotic stress signaling, and they are important candidates for preventing the loss of yield caused by exposure to environmental stresses. In a previous report, it was found that the ectopic-expression of Lobularia maritima stress-associated protein, LmSAP, conferred tolerance to abiotic and heavy metal stresses in transgenic tobacco plants. This study aimed to investigate the functions of the A20 and AN1 domains of LmSAP in salt and osmotic stress tolerance. To this end, in addition to the full-length LmSAP gene, we have generated three LmSAP-truncated forms (LmSAPΔA20, LmSAPΔAN1, and LmSAPΔA20-ΔAN1). Heterologous expression in Saccharomyces cerevisiae of different truncated forms of LmSAP revealed that the A20 domain is essential to increase cell tolerance to salt, ionic, and osmotic stresses. Transgenic tobacco plants overexpressing LmSAP and LmSAPΔAN1 constructs exhibited higher tolerance to salt and osmotic stresses in comparison to the non-transgenic plants (NT) and lines transformed with LmSAPΔA20 and LmSAPΔA20-ΔAN1 constructs. Similarly, transgenic plants overexpressing the full-length LmSAP gene and LmSAPΔAN1 truncated domain maintained higher superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) enzymatic activities due to the high expression levels of the genes encoding these key antioxidant enzymes, MnSOD, POD, and CAT1, as well as accumulated lower levels of malondialdehyde (MDA) under salt and osmotic stresses compared to NT and LmSAPΔA20 and LmSAPΔA20-ΔAN1 forms. These findings provide insights into the pivotal role of A20 and AN1 domains of LmSAP protein in salt and osmotic stress tolerance.

Zinc finger protein transcription factors: Integrated line of action for plant antimicrobial activity

The plants resist/tolerate unfavorable conditions in their natural habitats by using different but aligned and integrated defense mechanisms. Such defense responses include not only morphological and physiological adaptations but also the genomic and transcriptomic reconfiguration. Microbial attack on plants activates multiple pro-survival pathways such as transcriptional reprogramming, hypersensitive response (HR), antioxidant defense system and metabolic remodeling. Up-regulation of these processes during biotic stress conditions directly relates with plant survival. Over the years, hundreds of plant transcription factors (TFs) belonging to diverse families have been identified. Zinc finger protein (ZFP) TFs have crucial role in phytohormone response, plant growth and development, stress tolerance, transcriptional regulation, RNA binding and protein-protein interactions. Recent research progress has revealed regulatory and biological functions of ZFPs in incrementing plant resistance to pathogens. Integration of transcriptional activity with metabolic modulations has miniaturized plant innate immunity. However, the precise roles of different zinc finger TFs in plant immunity to pathogens have not been thoroughly analyzed. This review consolidates the pivotal functioning of zinc finger TFs and proposes the integrative understanding as foundation for the plant growth and development including the stress responses.

Banana sRNAome and degradome identify microRNAs functioning in differential responses to temperature stress

Background

Temperature stress is a major environmental factor affecting not only plant growth and development, but also fruit postharvest life and quality. MicroRNAs (miRNAs) are a class of non-coding small RNAs that play important roles in various biological processes. Harvested banana fruit can exhibit distinct symptoms in response to different temperature stresses, but the underlying miRNA-mediated regulatory mechanisms remained unknown.

Results

Here, we profiled temperature-responsive miRNAs in banana, using deep sequencing and computational and molecular analyses. In total 113 known miRNAs and 26 novel banana-specific miRNAs were identified. Of these miRNAs, 42 miRNAs were expressed differentially under cold and heat stresses. Degradome sequencing identified 60 target genes regulated by known miRNAs and half of these targets were regulated by 15 temperature-responsive miRNAs. The correlative expression patterns between several miRNAs and their target genes were further validated via qRT-PCR. Our data showed that miR535 and miR156 families may derive from a common ancestor during evolution and jointly play a role in fine-tuning SPL gene expression in banana. We also identified the miRNA-triggered phased secondary siRNAs in banana and found miR393-TIR1/AFB phasiRNA production displaying cold stress-specific enrichment.

Conclusions

Our results provide a foundation for understanding the miRNA-dependent temperature stress response in banana. The characterized correlations between miRNAs and their response to temperature stress could serve as markers in the breeding programs or tools for improving temperature tolerance of banana.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5395-1) contains supplementary material, which is available to authorized users.

Water stress in Musa spp.: A systematic review

BACKGROUND

The cultivation of bananas and other plants is limited by environmental stresses caused by climate change. In order to recognize physiological, biochemical and molecular components indicated to confer tolerance to water stress in Musa spp. we present the first systematic review on the topic.

METHODS

A systematic literature review was conducted using four databases for academic research (Google Academic, Springer, CAPES Journal Portal and PubMed Central). In order to avoid publication bias, a previously established protocol and inclusion and exclusion criteria were used.

RESULTS

The drought tolerance response is genotype-dependent, therefore the most studied varieties are constituted by the "B" genome. Tolerant plants are capable of super-expressing genes related to reisistance and defense response, maintaining the osmotic equilibrium and elimination of free radicals. Furthermore, they have higher amounts of water content, chlorophyll levels, stomatic conductance and dry root matter, when compared to susceptible plants.

CONCLUSIONS

In recent years, few integrated studies on the effects of water stress on bananas have been carried out and none related to flood stress. Therefore, we highlight the need for new studies on the mechanisms of differentially expressed proteins in response to stress regulation, post-translational mechanisms and epigenetic inheritance in bananas.

A stress-associated protein, LmSAP, from the halophyte Lobularia maritima provides tolerance to heavy metals in tobacco through increased ROS scavenging and metal detoxification processes

Agricultural soil pollution by heavy metals is a severe global ecological problem. We recently showed that overexpression of LmSAP, a member of the stress-associated protein (SAP) gene family isolated from Lobularia maritima, in transgenic tobacco led to enhanced tolerance to abiotic stress. In this study, we characterised the response of LmSAP transgenic tobacco plants to metal stresses (cadmium (Cd), copper (Cu), manganese (Mn), and zinc (Zn)). In L. maritima, LmSAP expression increased after 12 h of treatment with these metals, suggesting its involvement in the plant response to heavy metal stress. LmSAP transgenic tobacco plants subjected to these stress conditions were healthy, experienced higher seedling survival rates, and had longer roots than non-transgenic plants (NT). However, they exhibited higher tolerance towards cadmium and manganese than towards copper and zinc. LmSAP-overexpressing tobacco seedlings accumulated more cadmium, copper, and manganese compared with NT plants, but displayed markedly decreased hydrogen peroxide (H2O2) and lipid peroxidation levels after metal treatment. Activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) were significantly higher in transgenic plants than in NT plants after exposure to metal stress. LmSAP overexpression also enhanced the transcription of several genes encoding metallothioneins (Met1, Met2, Met3, Met4, and Met5), a copper transport protein CCH, a Cys and His-rich domain-containing protein RAR1 (Rar1), and a ubiquitin-like protein 5 (PUB1), which are involved in metal tolerance in tobacco. Our findings indicate that LmSAP overexpression in tobacco enhanced tolerance to heavy metal stress by protecting the plant cells against oxidative stress, scavenging reactive oxygen species (ROS), and decreasing the intracellular concentration of free heavy metals through its effect on metal-binding proteins in the cytosol.

Ectopic expression of a Musa acuminata root hair defective 3 (MaRHD3) in Arabidopsis enhances drought tolerance

Genetic improvement is an important approach for crop improvement towards yield stability in stress-prone areas. Functional analysis of candidate stress response genes can provide key information to allow the selection and modification of improved crop varieties. In this study, the constitutive expression of a banana cDNA, MaRHD3 in Arabidopsis improved the ability of transgenic lines to adapt to drought conditions. Transgenic Arabidopsis plants expressing MaRHD3 had roots with enhanced branching and more root hairs when challenged with drought stress. The MaRHD3 plants had higher biomass accumulation, higher relative water content, higher chlorophyll content and an increase in activity of reactive oxygen species (ROS) scavenging enzymes; SOD, CAT, GR, POD and APX with reduced water loss rates compared to control plants. The analysis of oxidative damage indicated lower cell membrane damage in transgenic lines compared to control plants. These findings, together with data from higher expression of ABF-3 and higher ABA content of drought-stressed transgenic MaRHD3 expressing plants, support the involvement of the ABA signal pathway and ROS scavenging enzyme systems in MaRHD3 mediated drought tolerance.

Genome-Wide Analysis and Cloning of the Apple Stress-Associated Protein Gene Family Reveals MdSAP15, Which Confers Tolerance to Drought and Osmotic Stresses in Transgenic Arabidopsis

Stress-associated proteins (SAPs) are novel A20/AN1 zinc finger domain-containing proteins that are now favorable targets to improve abiotic stress tolerance in plants. However, the SAP gene family and their biological functions have not been identified in the important fruit crop apple (Malus × domestica Borkh.). We conducted a genome-wide analysis and cloning of this gene family in apple and determined that the overexpression of MdSAP15 enhances drought tolerance in Arabidopsis plants. We identified 30 SAP genes in the apple genome. Phylogenetic analysis revealed two major groups within that family. Results from sequence alignments and analyses of 3D structures, phylogenetics, genomics structure, and conserved domains indicated that apple SAPs are highly and structurally conserved. Comprehensive qRT-PCR analysis found various expression patterns for MdSAPs in different tissues and in response to a water deficit. A transgenic analysis showed that the overexpression of MdSAP15 in transgenic Arabidopsis plants markedly enhanced their tolerance to osmotic and drought stresses. Our results demonstrate that the SAP genes are highly conserved in plant species, and that MdSAP15 can be used as a target gene in genetic engineering approaches to improve drought tolerance.

Expression and functional evaluation of CaZNF830 during pepper response to Ralstonia solanacearum or high temperature and humidity

Extensive transcriptional reprogramming after pathogen attack determines immunity to these invaders and plant development. Zinc finger (ZNF) transcription factors regulate important processes in plants such as development, vegetative activities and plant immunity. Despite their immense significance, majority of ZNF transcription factors (TF) involved in pepper immunity and resistance to heat stress have not been focused much. Herein, we identified and functionally characterized CaZNF830 in pepper defense against Ralstonia solanacearum inoculation (RSI) and tolerance to high temperature and high humidity (HTHH). Transient expression analysis of CaZNF830-GFP fusion protein in tobacco leaves revealed its localization to the nucleus. Transcription of CaZNF830 is induced in pepper plants upon RSI or HTHH. Consistent with this, fluorometric GUS enzymatic assay driven by pCaZNF830 presented significantly enhanced activity under RSI and HTHH in comparison with the control plants. The silencing of CaZNF830 by virus induced gene silencing (VIGS) significantly compromised pepper immunity against RSI with enhanced growth of Ralstonia solanacearum in pepper plants. Silencing of CaZNF830 also impaired tolerance to HTHH coupled with decreased expression levels of immunity and thermo-tolerance associated marker genes including CaHIR1, CaNPR1, CaPR1, CaABR1 and CaHSP24. By contrast, the transient over-expression of CaZNF830 in pepper leaves by infiltration of GV3101 cells containing 35S::CaZNF830-HA induced HR mimic cell death, H2O2 accumulation and activated the transcriptions of the tested defense-relative or thermo-tolerance associated marker genes. RT-PCR and immune-blotting assay confirmed the stable expression of HA-tagged CaZNF830 mRNA and protein in pepper. All these results suggest that CaZNF830 acts as a positive regulator of plant immunity against RSI or tolerance to HTHH, it is induced by RSI or HTHH and consequently activate pepper immunity against RSI or tolerance to HTHH by directly or indirectly transcriptional modulation of many defense-linked genes.

The LmSAP gene isolated from the halotolerant Lobularia maritima improves salt and ionic tolerance in transgenic tobacco lines

The A20/AN1 zinc-finger domain-containing proteins of the stress-associated proteins (SAPs) family are fast emerging as potential candidates for biotechnological approaches to improve abiotic stress tolerance in plants. We identified LmSAP, one of the SAPs genes in Lobularia maritima (L.) Desv., a halophyte brassicaceae, through its transcript accumulation in response to salinity and ionic stresses. Sequence homology analysis revealed that LmSAP contains two conserved zinc-finger domains A20 and AN1. Phylogeny analyses showed that LmSAP exhibited high amino acid sequence identity to other plant SAPs. Heterologous expression of LmSAP in yeast increased cell tolerance to salt and osmotic stress. In addition, the overexpression of LmSAP conferred high salt and ionic tolerance to transgenic tobacco plants. Transgenic tobacco seedlings showed higher survival rates and antioxidant activities under salt and ionic stresses. Enhanced antioxidant activities paralleled lower malondialdehyde and superoxide anion O2- levels in the LmSAP transgenic seedlings. Overall, our results suggest that overexpression of LmSAP enhanced salt tolerance by maintaining ionic balance and limiting oxidative and osmotic stresses.

Overexpression of native ferritin gene MusaFer1 enhances iron content and oxidative stress tolerance in transgenic banana plants

Iron is an indispensable element for plant growth and defense and hence it is essential to improve the plant's ability to accumulate iron. Besides, it is also an important aspect for human health. In view of this, we attempted to increase the iron content in banana cultivar Rasthali using MusaFer1 as a candidate gene. Initially, the expression of all five genes of the MusaFer family (MusaFer1-5) was quantified under iron-excess and -deficient conditions. The supplementation of 250 and 350 μM iron enhanced expression of all MusaFer genes; however, MusaFer1 was increased maximally by 2- and 4- fold in leaves and roots respectively. Under iron deficient condition, all five MusaFer genes were downregulated, indicating their iron dependent regulation. In MusaFer1 overexpressing lines, iron content was increased by 2- and 3-fold in leaves and roots respectively, as compared with that of untransformed lines. The increased iron was mainly localized in the epidermal regions of petiole. The analysis of MusaFer1 promoter indicated that it might control the expression of iron metabolism related genes and also other genes of MusaFer family. MusaFer1 overexpression led to downregulated expression of MusaFer3, MusaFer4 and MusaFer5 in transgenic leaves which might be associated with the plant's compensatory mechanism in response to iron flux. Other iron metabolism genes like Ferric reductase (FRO), transporters (IRT, VIT and YSL) and chelators (NAS, DMAS and NAAT) were also differentially expressed in transgenic leaf and root, suggesting the multifaceted impact of MusaFer1 towards iron uptake and organ distribution. Additionally, MusaFer1 overexpression increased plant tolerance against methyl viologen and excess iron which was quantified in terms of photosynthetic efficiency and malondialdehyde content. Thus, the study not only broadens our understanding about iron metabolism but also highlights MusaFer1 as a suitable candidate gene for iron fortification in banana.

Molecular cloning and expression analysis of duplicated polyphenol oxidase genes reveal their functional differentiations in sorghum

Polyphenol oxidase (PPO) is believed to play a role in plant growth, reproduction, and resistance to pathogens and pests. PPO causes browning of grains in cereals. In this study, genetic mapping of sorghum grain for phenol color reaction (PHR) was performed using a recombinant inbred line population. Only one locus was detected between SSR markers SM06072 and Xtxp176 on chromosome 6. Two linked orthologous genes (Sb06PPO1 and Sb06PPO2) within the mapped region were discovered and cloned. Transformation experiments using Nipponbare (a PHR negative rice cultivar) showed that Sb06PPO1 from LTR108 and two Sb06PPO2 alleles from both varieties could complement Nipponbare, whereas Sb06PPO1 from 654 could not. Subsequent quantitative real-time PCR (qPCR) experiments showed that Sb06PPO1 and Sb06PPO2 functioned diversely, Sb06PPO1 was mainly expressed in young panicles before flowering. Sb06PPO2 was strongly expressed in flowering panicles, especially in hulls and branches at filling stage. Moreover, the expression of Sb06PPO1 was found to be significantly up-regulated by exogenous ABA and salt, whereas Sb06PPO2 was not changed significantly, further demonstrating functional differentiation between the two genes.

Genetic engineering strategies for biotic and abiotic stress tolerance and quality enhancement in horticultural crops: a comprehensive review

Genetic engineering technique offers myriads of applications in improvement of horticultural crops for biotic and abiotic stress tolerance, and produce quality enhancement. During last two decades, a large number of transgenic horticultural crops has been developed and more are underway. A number of genes including natural and synthetic Cry genes, protease inhibitors, trypsin inhibitors and cystatin genes have been used to incorporate insect and nematode resistance. For providing protection against fungal and bacterial diseases, various genes like chitinase, glucanase, osmotin, defensin and pathogenesis-related genes are being transferred to many horticultural crops world over. RNAi technique has been found quite successful in inducing virus resistance in horticultural crops in addition to coat protein genes. Abiotic stresses such as drought, heat and salinity adversely affect production and productivity of horticultural crops and a number of genes encoding for biosynthesis of stress protecting compounds including mannitol, glycine betaine and heat shock proteins have been employed for abiotic stress tolerance besides various transcription factors like DREB1, MAPK, WRKY, etc. Antisense gene and RNAi technologies have revolutionized the pace of improvement of horticultural crops, particularly ornamentals for color modification, increasing shelf-life and reducing post-harvest losses. Precise genome editing tools, particularly CRISPR/Cas9, have been efficiently applied in tomato, petunia, citrus, grape, potato and apple for gene mutation, repression, activation and epigenome editing. This review provides comprehensive overview to draw the attention of researchers for better understanding of genetic engineering advancements in imparting biotic and abiotic stress tolerance as well as on improving various traits related to quality, texture, plant architecture modification, increasing shelf-life, etc. in different horticultural crops.

Expression of the Aeluropus littoralis AlSAP Gene Enhances Rice Yield under Field Drought at the Reproductive Stage

We evaluated the yields of Oryza sativa L. 'Nipponbare' rice lines expressing a gene encoding an A20/AN1 domain stress-associated protein, AlSAP, from the halophyte grass Aeluropus littoralis under the control of different promoters. Three independent field trials were conducted, with drought imposed at the reproductive stage. In all trials, the two transgenic lines, RN5 and RN6, consistently out-performed non-transgenic (NT) and wild-type (WT) controls, providing 50-90% increases in grain yield (GY). Enhancement of tillering and panicle fertility contributed to this improved GY under drought. In contrast with physiological records collected during previous greenhouse dry-down experiments, where drought was imposed at the early tillering stage, we did not observe significant differences in photosynthetic parameters, leaf water potential, or accumulation of antioxidants in flag leaves of AlSAP-lines subjected to drought at flowering. However, AlSAP expression alleviated leaf rolling and leaf drying induced by drought, resulting in increased accumulation of green biomass. Therefore, the observed enhanced performance of the AlSAP-lines subjected to drought at the reproductive stage can be tentatively ascribed to a primed status of the transgenic plants, resulting from a higher accumulation of biomass during vegetative growth, allowing reserve remobilization and maintenance of productive tillering and grain filling. Under irrigated conditions, the overall performance of AlSAP-lines was comparable with, or even significantly better than, the NT and WT controls. Thus, AlSAP expression inflicted no penalty on rice yields under optimal growth conditions. Our results support the use of AlSAP transgenics to reduce rice GY losses under drought conditions.

Regulation of Banana Phytoene Synthase (MaPSY) Expression, Characterization and Their Modulation under Various Abiotic Stress Conditions

Phytoene synthase (PSY) is a key regulatory enzyme of carotenoid biosynthesis pathway in plants. The present study examines the role of PSY in carotenogenesis and stress management in banana. Germplasm screening of 10 Indian cultivars showed that Nendran (3011.94 μg/100 g dry weight) and Rasthali (105.35 μg/100 g dry weight) contained the highest and lowest amounts of β-carotene, respectively in ripe fruit-pulp. Nendran ripe pulp also showed significantly higher antioxidant activity as compared to Rasthali. Meta-analysis of three banana PSY genes (MaPSY1, MaPSY2, and MaPSY3) was performed to identify their structural features, subcellular, and chromosomal localization in banana genome. The distinct expression patterns of MaPSY1, MaPSY2, and MaPSY3 genes were observed in various tissues, and fruit developmental stages of these two contrasting cultivars, suggesting differential regulation of the banana PSY genes. A positive correlation was observed between the expression of MaPSY1 and β-carotene accumulation in the ripe fruit-peel and pulp of Nendran. The presence of stress responsive cis-regulatory motifs in promoter region of MaPSY genes were correlated with the expression pattern during various stress (abscisic acid, methyl jasmonate, salicylic acid and dark) treatments. The positive modulation of MaPSY1 noticed under abiotic stresses suggested its role in plant physiological functions and defense response. The amino acid sequence analysis of the PSY proteins in contrasting cultivars revealed that all PSY comprises conserved domains related to enzyme activity. Bacterial complementation assay has validated the functional activity of six PSY proteins and among them PSY1 of Nendran (Nen-PSY1) gave the highest activity. These data provide new insights into the regulation of PSY expression in banana by developmental and stress related signals that can be explored in the banana improvement programs.

Isolation and characterization of LcSAP, a Leymus chinensis gene which enhances the salinity tolerance of Saccharomyces cerevisiae

A number of members of the SAP ("stress-associated protein") gene family have been implicated in the plant stress response. Here, a SAP gene has been isolated using PCR RACE from the perennial grass Leymus chinensis, a species which has reputation for ecological adaptability. The 17.6 kDa LcSAP product comprised 161 residues, including both an A20 domain and an AN1 domain, a feature of type I SAPs. Using a semi-quantitative RT-PCR assay to profile its transcription, it was shown that LcSAP was more strongly transcribed in the leaf than in the root under control conditions. The level of LcSAP transcription began to rise 6 h after the plant's exposure to 400 mM NaCl, and the abundance of transcript remained stable for at least 24 h. Exposing the plant to 100 mM Na₂CO₃ also induced LcSAP transcription, but the abundance of SAP transcript faded after 6 h. When LcSAP was introduced into yeast cells, the transgenic cells grew better than wild type ones when the medium contained 1.4 M NaCl. The ability of LcSAP to respond to salinity stress in yeast suggests that it also makes a contribution to the stress tolerance shown by L. chinensis.

Genome-wide Expression Analysis and Metabolite Profiling Elucidate Transcriptional Regulation of Flavonoid Biosynthesis and Modulation under Abiotic Stresses in Banana

Flavonoid biosynthesis is largely regulated at the transcriptional level due to the modulated expression of genes related to the phenylpropanoid pathway in plants. Although accumulation of different flavonoids has been reported in banana, a staple fruit crop, no detailed information is available on regulation of the biosynthesis in this important plant. We carried out genome-wide analysis of banana (Musa acuminata, AAA genome) and identified 28 genes belonging to 9 gene families associated with flavonoid biosynthesis. Expression analysis suggested spatial and temporal regulation of the identified genes in different tissues of banana. Analysis revealed enhanced expression of genes related to flavonol and proanthocyanidin (PA) biosynthesis in peel and pulp at the early developmental stages of fruit. Genes involved in anthocyanin biosynthesis were highly expressed during banana fruit ripening. In general, higher accumulation of metabolites was observed in the peel as compared to pulp tissue. A correlation between expression of genes and metabolite content was observed at the early stage of fruit development. Furthermore, this study also suggests regulation of flavonoid biosynthesis, at transcriptional level, under light and dark exposures as well as methyl jasmonate (MJ) treatment in banana.

Identification of Differentially-Expressed Genes in Response to Mycosphaerella fijiensis in the Resistant Musa Accession 'Calcutta-4' Using Suppression Subtractive Hybridization

Bananas and plantains are considered an important crop around the world. Banana production is affected by several constraints, of which Black Sigatoka Disease, caused by the fungus Mycosphaerella fijiensis, is considered one of the most important diseases in banana plantations. The banana accession ‘Calcutta-4’ has a natural resistance to Black Sigatoka; however, the fruit is not valuable for commercialization. Gene identification and expression studies in ‘Calcutta-4’ might reveal possible gene candidates for resistant to the disease and elucidate mechanisms for resistance. A subtracted cDNA library was generated from leaves after 6, 9 and 12 days inoculated with M. fijiensis conidia on greenhouse banana plants of the accession ‘Calcutta-4’. Bioinformatic analysis revealed 99 good quality sequences. Blast2go analysis revealed that 31% of the sequences could not be categorized and, according to the Biological Process Category, 32 and 28 ESTs are related to general metabolic and cellular processes, respectively; while 10 ESTs response to stimulus. Seven sequences were redundant and one was similar to genes that may be involved in pathogen resistance including the putative disease resistance protein RGA1. Genes encoding zinc finger domains were identified and may play an important role in pathogen resistance by inducing the expression of downstream genes. Expression analysis of four selected genes was performed using RT-qPCR during the early stage of the disease development at 6, 9, 12 and 15 days post inoculation showing a peak of up regulation at 9 or 12 days post inoculation. Three of the four genes showed an up-regulation of expression in ‘Calcutta-4’ when compared to ‘Williams’ after inoculation with M. fijiensis, suggesting a fine regulation of specific gene candidates that may lead to a resistance response. The genes identified in early responses in a plant-pathogen interaction may be relevant for the resistance response of ‘Calcutta-4’ to Black Sigatoka. Genes with different functions may play a role in plant response to the disease. The present study suggests a fine up regulation of these genes that might be needed to perform an incompatible interaction. Further gene functional studies need to be performed to validate their use as candidate resistance genes in susceptible banana cultivars.

The Banana Transcriptional Repressor MaDEAR1 Negatively Regulates Cell Wall-Modifying Genes Involved in Fruit Ripening

Ethylene plays an essential role in many biological processes including fruit ripening via modulation of ethylene signaling pathway. Ethylene Response Factors (ERFs) are key transcription factors (TFs) involved in ethylene perception and are divided into AP2, RAV, ERF, and DREB sub-families. Although a number of studies have implicated the involvement of DREB sub-family genes in stress responses, little is known about their roles in fruit ripening. In this study, we identified a DREB TF with a EAR motif, designated as MaDEAR1, which is a nucleus-localized transcriptional repressor. Expression analysis indicated that MaDEAR1 expression was repressed by ethylene, with reduced levels of histone H3 and H4 acetylation at its regulatory regions during fruit ripening. In addition, MaDEAR1 promoter activity was also suppressed in response to ethylene treatment. More importantly, MaDEAR1 directly binds to the DRE/CRT motifs in promoters of several cell wall-modifying genes including MaEXP1/3, MaPG1, MaXTH10, MaPL3, and MaPME3 associated with fruit softening during ripening and represses their activities. These data suggest that MaDEAR1 acts as a transcriptional repressor of cell wall-modifying genes, and may be negatively involved in ethylene-mediated ripening of banana fruit. Our findings provide new insights into the involvement of DREB TFs in the regulation of fruit ripening.

Rice Stress Associated Protein 1 (OsSAP1) Interacts with Aminotransferase (OsAMTR1) and Pathogenesis-Related 1a Protein (OsSCP) and Regulates Abiotic Stress Responses

Stress associated proteins (SAPs) are the A20/AN1 zinc-finger containing proteins which can regulate the stress signaling in plants. The rice SAP protein, OsSAP1 has been shown to confer abiotic stress tolerance to plants, when overexpressed, by modulating the expression of endogenous stress-related genes. To further understand the mechanism of OsSAP1-mediated stress signaling, OsSAP1 interacting proteins were identified using yeast two-hybrid analysis. Two novel proteins, aminotransferase (OsAMTR1) and a SCP/TAPS or pathogenesis-related 1 class of protein (OsSCP) were found to interact with OsSAP1. The genes encoding OsAMTR1 and OsSCP were stress-responsive and showed higher expression upon abiotic stress treatments. The role of OsAMTR1 and OsSCP under stress was analyzed by overexpressing them constitutively in Arabidopsis and responses of transgenic plants were assessed under salt and water-deficit stress. The OsAMTR1 and OsSCP overexpressing plants showed higher seed germination, root growth and fresh weight than wild-type plants under stress conditions. Overexpression of OsAMTR1 and OsSCP affected the expression of many known stress-responsive genes which were not affected by the overexpression of OsSAP1. Moreover, the transcript levels of OsSCP and OsAMTR1 were also unaffected by the overexpression of OsSAP1. Hence, it was concluded that OsSAP1 regulates the stress responsive signaling by interacting with these proteins which further regulate the downstream stress responsive gene expression.

Genome-Wide Identification and Expression Analysis of Homeodomain Leucine Zipper Subfamily IV (HDZ IV) Gene Family from Musa accuminata

The homeodomain zipper family (HD-ZIP) of transcription factors is present only in plants and plays important role in the regulation of plant-specific processes. The subfamily IV of HDZ transcription factors (HD-ZIP IV) has primarily been implicated in the regulation of epidermal structure development. Though this gene family is present in all lineages of land plants, members of this gene family have not been identified in banana, which is one of the major staple fruit crops. In the present work, we identified 21 HDZIV encoding genes in banana by the computational analysis of banana genome resource. Our analysis suggested that these genes putatively encode proteins having all the characteristic domains of HDZIV transcription factors. The phylogenetic analysis of the banana HDZIV family genes further confirmed that after separation from a common ancestor, the banana, and poales lineages might have followed distinct evolutionary paths. Further, we conclude that segmental duplication played a major role in the evolution of banana HDZIV encoding genes. All the identified banana HDZIV genes expresses in different banana tissue, however at varying levels. The transcript levels of some of the banana HDZIV genes were also detected in banana fruit pulp, suggesting their putative role in fruit attributes. A large number of genes of this family showed modulated expression under drought and salinity stress. Taken together, the present work lays a foundation for elucidation of functional aspects of the banana HDZIV encoding genes and for their possible use in the banana improvement programs.

An A20/AN1-type zinc finger protein modulates gibberellins and abscisic acid contents and increases sensitivity to abiotic stress in rice (Oryza sativa)

The plant hormones gibberellins (GA) and abscisic acid (ABA) play important roles in plant development and stress responses. Here we report a novel A20/AN1-type zinc finger protein ZFP185 involved in GA and ABA signaling in the regulation of growth and stress response. ZFP185 was constitutively expressed in various rice tissues. Overexpression of ZFP185 in rice results in a semi-dwarfism phenotype, reduced cell size, and the decrease of endogenous GA3 content. By contrast, higher GA3 content was observed in RNAi plants. The application of exogenous GA3 can fully rescue the semi-dwarfism phenotype of ZFP185 overexpressing plants, suggesting the negative role of ZFP185 in GA biosynthesis. Besides GA, overexpression of ZFP185 decreased ABA content and expression of several ABA biosynthesis-related genes. Moreover, it was found that ZFP185, unlike previously known A20/AN1-type zinc finger genes, increases sensitivity to drought, cold, and salt stresses, implying the negative role of ZFP185 in stress tolerance. ZFP185 was localized in the cytoplasm and lacked transcriptional activation potential. Our study suggests that ZFP185 regulates plant growth and stress responses by affecting GA and ABA biosynthesis in rice.

Selection of reference genes for quantitative real-time PCR normalization in creeping bentgrass involved in four abiotic stresses

This study identified stable reference genes for normalization of gene expression data in qRT-PCR analysis of leaf and root tissues in creeping bentgrass under four abiotic stresses. Examination of gene expression using quantitative real-time PCR (qRT-PCR) in plant responses to abiotic stresses can provide valuable information for stress-tolerance improvement. Selecting stable reference genes for qRT-PCR analysis is critically important. The objective of this study was to determine the stability of expression for eight candidate reference genes (ACT, EF1a, TUB, UPL7, GAPDH, PP2A, PEPKR1, and CACS) in two tissues (roots and leaves) of a perennial grass species under four abiotic stresses (salt, drought, cold, and heat) using four programs (GeNorm, NormFinder, BestKeeper, and RefFinder). The results showed that (1) the combinations of CACS and UPL7 or PP2A and ACT were stably expressed in salt-treated roots or leaves; (2) the combinations of GAPDH and CACS or PP2A and PEPKR1 were stable in roots and leaves under drought stress; (3) CACS and PP2A exhibited stable expression in cold-treated roots and the combination of EF1a and UPL7 was also stable in cold-treated leaves; and (4) CACS and PP2A were the two most stable reference genes in heat-stressed roots and UPL7 combined with GAPDH and PP2A was stably expressed in heat-stressed leaves. The qRT-PCR analysis of a target gene, AsSAP expression patterns in response to salinity and drought stress, confirmed the reliability of those selected and stable reference genes. Identification of stable reference genes in creeping bentgrass will improve assay accuracy for selecting stress-tolerance genes and identifying molecular mechanisms conferring stress tolerance in this species.

Constitutive and stress-inducible overexpression of a native aquaporin gene (MusaPIP2;6) in transgenic banana plants signals its pivotal role in salt tolerance

High soil salinity constitutes a major abiotic stress and an important limiting factor in cultivation of crop plants worldwide. Here, we report the identification and characterization of a aquaporin gene, MusaPIP2;6 which is involved in salt stress signaling in banana. MusaPIP2;6 was firstly identified based on comparative analysis of stressed and non-stressed banana tissue derived EST data sets and later overexpression in transgenic banana plants was performed to study its tangible functions in banana plants. The overexpression of MusaPIP2;6 in transgenic banana plants using constitutive or inducible promoter led to higher salt tolerance as compared to equivalent untransformed control plants. Cellular localization assay performed using transiently transformed onion peel cells indicated that MusaPIP2;6 protein tagged with green fluorescent protein was translocated to the plasma membrane. MusaPIP2;6-overexpressing banana plants displayed better photosynthetic efficiency and lower membrane damage under salt stress conditions. Our results suggest that MusaPIP2;6 is involved in salt stress signaling and tolerance in banana.

A ripening-induced transcription factor MaBSD1 interacts with promoters of MaEXP1/2 from banana fruit

KEY MESSAGE

The ripening-induced MaBSD1 acts as a transcriptional activator, and might be involved in banana fruit ripening partly through directly activating the expression of two ripening-associated genes, MaEXP1/2. BSD (BTF2-like transcription factors, synapse-associated proteins and DOS2-like proteins) transcription factors are characterized by a typical BSD domain. However, little information is available concerning their possible roles in plant growth and development, especially in fruit ripening. In the present study, one BSD gene, designated as MaBSD1, was isolated from banana fruit. MaBSD1 has an open reading frame (ORF) of 921 bp which encodes a polypeptide of 306 amino acid residues with molecular weight of 34.80 kDa, and isoelectric point (pI) of 4.54. Subcellular localization and transcriptional activation assays showed that MaBSD1 was localized in both the nucleus and cytoplasm and possessed transcriptional activity. RT-qPCR and promoter activity analysis indicated that MaBSD1 was ethylene and ripening inducible, and the accumulation of MaBSD1 transcript was correlated well with the evolution of ethylene production and ripening process. Moreover, transient assay showed that MaBSD1 could activate the expression of two cell wall modification-related genes, MaEXP1/2, via directly interacting with their promoters. Together, these data suggest that ripening-induced MaBSD1 acts as a transcriptional activator and might be associated with banana fruit ripening, at least partially through directly activating the expression of MaEXP1/2, expanding the limited information concerning the BSD transcription factor in relation to fruit ripening.

OsiSAP1 overexpression improves water-deficit stress tolerance in transgenic rice by affecting expression of endogenous stress-related genes

OsiSAP1, an A20/AN1 zinc-finger protein, confers water-deficit stress tolerance at different stages of growth by affecting expression of several endogenous genes in transgenic rice. Transgenic lines have been generated from rice constitutively expressing OsiSAP1, an A20/AN1 zinc-finger containing stress-associated protein gene from rice, driven by maize UBIQUITIN gene promoter and evaluated for water-deficit stress tolerance at different stages of growth. Their seeds show early germination and seedlings grow better under water-deficit stress compared to non-transgenic (NT) rice. Leaves from transgenic seedlings showed lesser membrane damage and lipid peroxidation under water-deficit stress. Relatively lower rate of leaf water loss has been observed in detached intact leaves from transgenic plants during late vegetative stage. Delayed leaf rolling and higher relative water content were also observed in transgenic plants under progressive water-deficit stress during reproductive developmental stage. Although reduction in grain yield is observed under unstressed condition, the relative water-deficit stress-induced yield losses are lower in transgenic rice vis-à-vis NT plants thereby resulting in yield loss protection. Transcriptome analysis suggests that overexpression of OsiSAP1 in transgenic rice results in altered expression of several endogenous genes including those coding for transcription factors, membrane transporters, signaling components and genes involved in metabolism, growth and development. A total of 150 genes were found to be more than twofold up-regulated in transgenic rice of which 43 genes are known to be involved in stress response. Our results suggest that OsiSAP1 is a positive regulator of water-deficit stress tolerance in rice.

Rice SAPs are responsive to multiple biotic stresses and overexpression of OsSAP1, an A20/AN1 zinc-finger protein, enhances the basal resistance against pathogen infection in tobacco

Eukaryotic A20/AN1 zinc-finger proteins (ZFPs) play an important role in the regulation of immune and stress response. After elucidation of the role of first such protein, OsSAP1, in abiotic stress tolerance, 18 rice stress associated protein (SAP) genes have been shown to be regulated by multiple abiotic stresses. In the present study, expression pattern of all the 18 OsSAP genes have been analysed in response to different biotic stress simulators, in order to get insights into their possible involvement in biotic stress tolerance. Our results showed the upregulation of OsSAP1 and OsSAP11 by all biotic stress simulator treatments. Furthermore, the functional role of OsSAP1 in plant defence responses has been explored through overexpression in transgenic plants. Constitutive expression of OsSAP1 in transgenic tobacco resulted into enhanced disease resistance against virulent bacterial pathogen, together with the upregulation of known defence-related genes. Present investigation suggests that rice SAPs are responsive to multiple biotic stresses and OsSAP1 plays a key role in basal resistance against pathogen infection. This strongly supports the involvement of rice SAPs in cross-talk between biotic and abiotic stress signalling pathways, which makes them ideal candidate to design strategies for protecting crop plants against multiple stresses.