Sugarcane ScOPR1 gene enhances plant disease resistance through the modulation of hormonal signaling pathways.

KEY MESSAGE: Transgenic plants stably overexpressing ScOPR1 gene enhanced disease resistance by increasing the accumulation of JA, SA, and GST, as well as up-regulating the expression of genes related to signaling pathways. 12-Oxo-phytodienoate reductase (OPR) is an oxidoreductase that depends on flavin mononucleotide (FMN) and catalyzes the conversion of 12-oxophytodienoate (12-OPDA) into jasmonic acid (JA). It plays a key role in plant growth and development, and resistance to adverse stresses. In our previous study, we have obtained an OPR gene (ScOPR1, GenBank Accession Number: MG755745) from sugarcane. This gene showed positive responses to methyl jasmonate (MeJA), salicylic acid (SA), abscisic acid (ABA), and Sporisorium scitamineum, suggesting its potential for pathogen resistance. Here, in our study, we observed that Nicotiana benthamiana leaves transiently overexpressing ScOPR1 exhibited weaker disease symptoms, darker 3,3-diaminobenzidine (DAB) staining, higher accumulation of reactive oxygen species (ROS), and higher expression of hypersensitive response (HR) and SA pathway-related genes after inoculation with Ralstonia solanacearum and Fusarium solanacearum var. coeruleum. Furthermore, the transgenic N. benthamiana plants stably overexpressing the ScOPR1 gene showed enhanced resistance to pathogen infection by increasing the accumulation of JA, SA, and glutathione S-transferase (GST), as well as up-regulating genes related to HR, JA, SA, and ROS signaling pathways. Transcriptome analysis revealed that the specific differentially expressed genes (DEGs) in ScOPR1-OE were significantly enriched in hormone transduction signaling and plant-pathogen interaction pathways. Finally, a functional mechanism model of the ScOPR1 gene in response to pathogen infection was depicted. This study provides insights into the molecular mechanism of ScOPR1 and presents compelling evidence supporting its positive involvement in enhancing plant disease resistance.

Key Factors of Quality Formation in Wuyi Black Tea during Processing Timing.

As the most consumed tea in the world, all kinds of black tea are developed from Wuyi black tea. In this study, quality components, regulatory gene expression, and key enzyme activity during the processing were analyzed to illustrate the taste formation of WBT. Withering mainly affected the content of amino acids, while catechins and tea pigments were most influenced by rolling and the pre-metaphase of fermentation. Notably, regulatory gene expression was significantly down-regulated after withering except for polyphenoloxidase1, polyphenoloxidase2, leucoanthocyanidin dioxygenase, chalcone isomerase, and flavonoid 3', 5'-hydroxylase. Co-expression of flavonoid pathway genes confirmed similar expression patterns of these genes in the same metabolic pathway. Interestingly, rolling and fermentation anaphase had a great effect on polyphenol oxidase, and fermentation pre-metaphase had the greatest effect on cellulase. Since gene regulation mainly occurs before picking, the influence of chemical reaction was greater during processing. It was speculated that polyphenol oxidase and cellulase, which promoted the transformation of quality components, were the key factors in the quality formation of WBT. The above results provide theoretical basis for the processing of WBT and the reference for producing high-quality black tea.

Theory to practice: a success in breeding sugarcane variety YZ08-1609 known as the King of Sugar.

Sugarcane, a significant cash crop in tropical and subtropical regions, contributes to 80% of sugar production and 40% of bioethanol production in the world. It is a key sugar crop, accounting for 85% of sugar production in China. Developing new varieties with high yield, high sugar, and better stress resistance is crucial for the sustainable growth of sugar industry. Hybrid breeding is the most widely used and effective method, with over 98% of Chinese sugarcane varieties resulting from this approach. Over the past two decades, Chinese breeders have developed the theory of high-heterogeneous composite high-sugar breeding, leading to the successful breeding of the fifth-generation sugarcane varieties. Among them, YZ08-1609, a complex hybrid of Saccharum spp., was developed by Sugarcane Research Institute (YSRI) of Yunnan Academy of Agricultural Sciences. The average cane yield of YZ08-1609 was 14.4% higher than ROC22. It is highly resistant to mosaic disease, and highly tolerant to drought stress, but moderately susceptible to smut disease. Notably, YZ08-1609 stands out with a sucrose content of 20.3%, setting an international record, earning the reputation as "King of Sugar". To summarize experience and inspire breeding, we provided here the detailed insights into the selection of parents, breeding process, and characteristics of YZ08-1609. Besides, the biological mechanisms underlying its high yield and high sugar was excavated at both transcriptional and metabolic levels. The challenges and prospects in breeding sugarcane varieties especially with high sugar were also discussed, offering a foundation for the future development of high-sugar varieties.

Sugarcane ScCAX4 is a Negative Regulator of Resistance to Pathogen Infection.

Calcium (Ca2+) is a second messenger in various physiological processes within plants. The significance of the Ca2+/H+ exchanger (CAX) has been established in facilitating Ca2+ transport in plants; however, disease resistance functions of the CAX gene remain elusive. In this study, we conducted sequence characterization and expression analysis for a sugarcane CAX gene, ScCAX4 (GenBank Accession Number: MW206380). In order to further investigate the disease resistance functions, this gene was then transiently overexpressed in Nicotiana benthamiana leaves, which were subsequently inoculated with Fusarium solani var. coeruleum. Results showed that ScCAX4 overexpression increased the susceptibility of N. benthamiana to pathogen infection by regulating the expression of genes related to salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) pathways, suggesting its negative role in disease resistance. Furthermore, we genetically transformed the ScCAX4 gene into N. benthamiana and obtained three positive T2 generation lines. Interestingly, the symptomatology of transgenic plants was consistent with that of transient overexpression after pathogen inoculation. Notably, the JA content in transgenic overexpression lines was significantly higher than that in the wild-type. RNA-seq revealed that ScCAX4 could mediate multiple signaling pathways, and the JA signaling pathway played a key role in modulating disease resistance. Finally, a regulatory model was depicted for the increased susceptibility to pathogen infection conferred by the ScCAX4 gene. This study provides genetic resources for sugarcane molecular breeding and the research direction for plant CAX genes.

Transcriptional Regulation of SugarCane Response to Sporisorium scitamineum: Insights from Time-Course Gene Coexpression and Ca2+ Signaling.

Sugarcane response to Sporisorium scitamineum is determined by multiple major genes and numerous microeffector genes. Here, time-ordered gene coexpression networks were applied to explore the interaction between sugarcane and S. scitamineum. Totally, 2459 differentially expressed genes were identified and divided into 10 levels, and several stress-related subnetworks were established. Interestingly, the Ca2+ signaling pathway was activated to establish the response to sugarcane smut disease. Accordingly, two CAX genes (ScCAX2 and ScCAX3) were cloned and characterized from sugarcane. They were significantly upregulated under ABA stress but inhibited by MeJA treatment. Furthermore, overexpression of ScCAX2 and ScCAX3 enhanced the susceptibility of transgenic plants to the pathogen infection, suggesting its negative role in disease resistance. A regulatory model for ScCAX genes in disease response was thus depicted. This work helps to clarify the transcriptional regulation of sugarcane response to S. scitamineum stress and the function of the CAX gene in disease response.

Sugarcane breeding: a fantastic past and promising future driven by technology and methods.

Sugarcane is the most important sugar and energy crop in the world. During sugarcane breeding, technology is the requirement and methods are the means. As we know, seed is the cornerstone of the development of the sugarcane industry. Over the past century, with the advancement of technology and the expansion of methods, sugarcane breeding has continued to improve, and sugarcane production has realized a leaping growth, providing a large amount of essential sugar and clean energy for the long-term mankind development, especially in the face of the future threats of world population explosion, reduction of available arable land, and various biotic and abiotic stresses. Moreover, due to narrow genetic foundation, serious varietal degradation, lack of breakthrough varieties, as well as long breeding cycle and low probability of gene polymerization, it is particularly important to realize the leapfrog development of sugarcane breeding by seizing the opportunity for the emerging Breeding 4.0, and making full use of modern biotechnology including but not limited to whole genome selection, transgene, gene editing, and synthetic biology, combined with information technology such as remote sensing and deep learning. In view of this, we focus on sugarcane breeding from the perspective of technology and methods, reviewing the main history, pointing out the current status and challenges, and providing a reasonable outlook on the prospects of smart breeding.

Molecular identification and functional characterization of a transcription factor GeRAV1 from Gelsemium elegans.

BACKGROUND: Gelsemium elegans is a traditional Chinese medicinal plant and temperature is one of the key factors affecting its growth. RAV (related to ABI3/VP1) transcription factor plays multiple roles in higher plants, including the regulation of plant growth, development, and stress response. However, RAV transcription factor in G. elegans has not been reported. RESULTS: In this study, three novel GeRAV genes (GeRAV1-GeRAV3) were identified from the transcriptome of G. elegans under low temperature stress. Phylogenetic analysis showed that GeRAV1-GeRAV3 proteins were clustered into groups II, IV, and V, respectively. RNA-sequencing (RNA-seq) and real-time quantitative PCR (qRT-PCR) analyses indicated that the expression of GeRAV1 and GeRAV2 was increased in response to cold stress. Furthermore, the GeRAV1 gene was successfully cloned from G. elegans leaf. It encoded a hydrophilic, unstable, and non-secretory protein that contained both AP2 and B3 domains. The amino acid sequence of GeRAV1 protein shared a high similarity of 81.97% with Camptotheca acuminata CaRAV. Subcellular localization and transcriptional self-activation experiments demonstrated that GeRAV1 was a nucleoprotein without self-activating activity. The GeRAV1 gene was constitutively expressed in the leaves, stems, and roots of the G. elegans, with the highest expression levels in roots. In addition, the expression of the GeRAV1 gene was rapidly up-regulated under abscisic acid (ABA), salicylic acid (SA), and methyl jasmonate (MeJA) stresses, suggesting that it may be involved in hormonal signaling pathways. Moreover, GeRAV1 conferred improved cold and sodium chloride tolerance in Escherichia coli Rosetta cells. CONCLUSIONS: These findings provided a foundation for further understanding on the function and regulatory mechanism of the GeRAV1 gene in response to low-temperature stress in G. elegans.

Complete mitogenome assembly of Selenicereus monacanthus revealed its molecular features, genome evolution, and phylogenetic implications.

BACKGROUND: Mitochondria are the powerhouse of the cell and are critical for plant growth and development. Pitaya (Selenicereus or Hylocereus) is the most important economic crop in the family Cactaceae and is grown worldwide, however its mitogenome is unreported. RESULTS: This study assembled the complete mitogenome of the red skin and flesh of pitaya (Selenicereus monacanthus). It is a full-length, 2,290,019 bp circular molecule encoding 59 unique genes that only occupy 2.17% of the entire length. In addition, 4,459 pairs of dispersed repeats (≥ 50 bp) were identified, accounting for 84.78% of the total length, and three repeats (394,588, 124,827, and 13,437 bp) mediating genomic recombination were identified by long read mapping and Sanger sequencing. RNA editing events were identified in all 32 protein-coding genes (PCGs), among which four sites (nad1-2, nad4L-2, atp9-copy3-223, and ccmFC-1309) were associated with the initiation or termination of PCGs. Seventy-eight homologous fragments of the chloroplast genome were identified in the mitogenome, the longest having 4,523 bp. In addition, evolutionary analyses suggest that S. monacanthus may have undergone multiple genomic reorganization events during evolution, with the loss of at least nine PCGs (rpl2, rpl10, rps2, rps3, rps10, rps11, rps14, rps19, and sdh3). CONCLUSIONS: This study revealed the genetic basis of the S. monacanthus mitogenome, and provided a scientific basis for further research on phenotypic traits and germplasm resource development.

Deep learning-empowered crop breeding: intelligent, efficient and promising.

Crop breeding is one of the main approaches to increase crop yield and improve crop quality. However, the breeding process faces challenges such as complex data, difficulties in data acquisition, and low prediction accuracy, resulting in low breeding efficiency and long cycle. Deep learning-based crop breeding is a strategy that applies deep learning techniques to improve and optimize the breeding process, leading to accelerated crop improvement, enhanced breeding efficiency, and the development of higher-yielding, more adaptive, and disease-resistant varieties for agricultural production. This perspective briefly discusses the mechanisms, key applications, and impact of deep learning in crop breeding. We also highlight the current challenges associated with this topic and provide insights into its future application prospects.

Assembly and analysis of the first complete mitochondrial genome of Punica granatum and the gene transfer from chloroplast genome.

Pomegranate (Punica granatum L.) is one of the oldest fruits with edible, medicinal and ornamental values. However, there is no report on the mitochondrial genome of pomegranate. In this study, the mitochondrial genome of P. granatum was sequenced, assembled and analyzed in detail, while the chloroplast genome was assembled using the same set of data. The results showed that the P. granatum mitogenome had a multi branched structure, using BGI + Nanopore mixed assembly strategy. The total genome length was 404,807 bp, with the GC content of 46.09%, and there were 37 protein coding genes, 20 tRNA genes and three rRNA genes. In the whole genome, 146 SSRs were identified. Besides, 400 pairs of dispersed repeats were detected, including 179 palindromic, 220 forward and one reverse. In the P. granatum mitochondrial genome, 14 homologous fragments of chloroplast genome were found, accounting for 0.54% of the total length. Phylogenetic analysis showed that among the published mitochondrial genomes of related genera, P. granatum had the closest genetic relationship with Lagerstroemia indica of Lythraceae. The 580 and 432 RNA editing sites were predicted on 37 protein coding genes of mitochondrial genome using BEDTools software and online website PREPACT respectively, but all were from C to U, of which ccmB and nad4 gene were most frequently edited, with 47 sites. This study provides a theoretical basis for understanding the evolution of higher plants, species classification and identification, and will also be useful for further utilization of pomegranate germplasm resources.

Deciphering the Atlas of Post-Translational Modification in Sugarcane.

In plants, lysine acetylation (Kac), 2-hydroxyisobutyrylation (Khib), and lysine lactylation (Kla), the three new types of post-translational modification (PTM), play very important roles in growth, development, and resistance to adverse environmental stresses. Herein, we report the first global acetylome, 2-hydroxyisobutyrylome, and lactylome in sugarcane. A total of 8573 Kac, 4637 Khib, and 215 Kla sites across 3903, 1507, and 139 modified proteins were identified. Besides, homology analyses revealed the Kac, Khib, and Kla sites on histones were conserved between sugarcane and rice or poplar. Functional annotations demonstrated that the Kac, Khib, and Kla proteins were mainly involved in energy metabolism. In addition, a number of modified transcription factors and stress-related proteins, which were constitutively expressed in different tissues of sugarcane and induced by drought, cold or Sporisorium scitamineum stress, were identified. Finally, a proposed working mode on how PTM functions in sugarcane was depicted. We thus concluded that PTM should play a role in sugarcane growth, development, and response to biotic and abiotic stresses, but the mechanisms require further investigation. The present study provided the all-new comprehensive profile of proteins Kac, Khib, and Kla and a new perspective to understand the molecular mechanisms of protein PTMs in sugarcane.

Transcriptomic and Proteomic Landscape of Sugarcane Response to Biotic and Abiotic Stressors.

Sugarcane, a C4 plant, provides most of the world's sugar, and a substantial amount of renewable bioenergy, due to its unique sugar-accumulating and feedstock properties. Brazil, India, China, and Thailand are the four largest sugarcane producers worldwide, and the crop has the potential to be grown in arid and semi-arid regions if its stress tolerance can be improved. Modern sugarcane cultivars which exhibit a greater extent of polyploidy and agronomically important traits, such as high sugar concentration, biomass production, and stress tolerance, are regulated by complex mechanisms. Molecular techniques have revolutionized our understanding of the interactions between genes, proteins, and metabolites, and have aided in the identification of the key regulators of diverse traits. This review discusses various molecular techniques for dissecting the mechanisms underlying the sugarcane response to biotic and abiotic stresses. The comprehensive characterization of sugarcane's response to various stresses will provide targets and resources for sugarcane crop improvement.

Grapevine double cropping: a magic technology.

Grapevine is one of the most important fruit trees in the world, but it is often threatened by various biotic and abiotic stresses in production, resulting in decreased yield and quality. Grapevine double cropping in one year is a kind of preparatory and artificial control technology, which can not only save the loss of natural disasters, but also plays an important role in staggering the peak to market, thus increasing yield and improving the quality of grape fruit. This perspective provides a concise discussion of the physiological basis, the main determinants, and their impacts on yield and fruit quality of grapevine double cropping. We also highlight the current challenges around this theme and prospect its application in the future.

Dissecting the features of TGA gene family in Saccharum and the functions of ScTGA1 under biotic stresses.

Sugarcane is an important sugar and energy crop and smut disease caused by Sporisorium scitamineum is a major fungal disease which can seriously reduce the yield and quality of sugarcane. In plants, TGACG motif binding (TGA) transcription factors are involved in the regulation of salicylic acid (SA) and methyl jasmonate (MeJA) signaling pathways, as well as in response to various biotic and abiotic stresses. However, no TGA-related transcription factor has been reported in Saccharum. In the present study, 44 SsTGA genes were identified from Saccharum spontaneum, and were assorted into three clades (I, II, III). Cis-regulatory elements (CREs) analysis revealed that SsTGA genes may be involved in hormone and stress response. RNA-seq data and RT-qPCR analysis indicated that SsTGAs were constitutively expressed in different tissues and induced by S. scitamineum stress. In addition, a ScTGA1 gene (GenBank accession number ON416997) was cloned from the sugarcane cultivar ROC22, which was homologous to SsTGA1e in S. spontaneum and encoded a nucleus protein. It was constitutively expressed in sugarcane tissues and up-regulated by SA, MeJA and S. scitamineum stresses. Furthermore, transient overexpression of ScTGA1 in Nicotiana benthamiana could enhance its resistance to the infection of Ralstonia solanacearum and Fusarium solani var. coeruleum, by regulating the expression of immune genes related to hypersensitive response (HR), ethylene (ET), SA and jasmonic acid (JA) pathways. This study should contribute to our understanding on the evolution and function of the SsTGA gene family in Saccharum, and provide a basis for the functional identification of ScTGA1 under biotic stresses.

Identification and Expression Analysis of Hexokinases Family in Saccharum spontaneum L. under Drought and Cold Stresses.

In plants, the multi-gene family of dual-function hexokinases (HXKs) plays an important role in sugar metabolism and sensing, that affects growth and stress adaptation. Sugarcane is an important sucrose crop and biofuel crop. However, little is known about the HXK gene family in sugarcane. A comprehensive survey of sugarcane HXKs, including physicochemical properties, chromosomal distribution, conserved motifs, and gene structure was conducted, identifying 20 members of the SsHXK gene family that were located on seven of the 32 Saccharum spontaneum L. chromosomes. Phylogenetic analysis showed that the SsHXK family could be divided into three subfamilies (group I, II and III). Motifs and gene structure were related to the classification of SsHXKs. Most SsHXKs contained 8-11 introns which was consistent with other monocots. Duplication event analysis indicated that HXKs in S. spontaneum L. primarily originated from segmental duplication. We also identified putative cis-elements in the SsHXK promoter regions which were involved in phytohormone, light and abiotic stress responses (drought, cold et al.). During normal growth and development, 17 SsHXKs were constitutively expressed in all ten tissues. Among them, SsHXK2, SsHXK12 and SsHXK14 had similar expression patterns and were more highly expressed than other genes at all times. The RNA-seq analysis showed that 14/20 SsHXKs had the highest expression level after cold stress for 6 h, especially SsHXK15, SsHXK16 and SsHXK18. As for drought treatment, 7/20 SsHXKs had the highest expression level after drought stress for 10 days, 3/20 (SsHKX1, SsHKX10 and SsHKX11) had the highest expression level after 10 days of recovery. Overall, our results revealed the potential biological function of SsHXKs, which may provide information for in-depth functional verification.

Identification of QTLs and critical genes related to sugarcane mosaic disease resistance.

Mosaic viral diseases affect sugarcane productivity worldwide. Mining disease resistance-associated molecular markers or genes is a key component of disease resistance breeding programs. In the present study, 285 F1 progeny were produced from a cross between Yuetang 93-159, a moderately resistant variety, and ROC22, a highly susceptible variety. The mosaic disease symptoms of these progenies, with ROC22 as the control, were surveyed by natural infection under 11 different environmental conditions in the field and by artificial infections with a mixed sugarcane mosaic virus (SCMV) and sorghum mosaic virus (SrMV) inoculum. Analysis of consolidated survey data enabled the identification of 29 immune, 55 highly resistant, 70 moderately resistant, 62 susceptible, and 40 highly susceptible progenies. The disease response data and a high-quality SNP genetic map were used in quantitative trait locus (QTL) mapping. The results showed that the correlation coefficients (0.26~0.91) between mosaic disease resistance and test environments were significant (p< 0.001), and that mosaic disease resistance was a highly heritable quantitative trait (H2 = 0.85). Seven mosaic resistance QTLs were located to the SNP genetic map, each QTL accounted for 3.57% ~ 17.10% of the phenotypic variation explained (PVE). Furthermore, 110 pathogen response genes and 69 transcription factors were identified in the QTLs interval. The expression levels of nine genes (Soffic.07G0015370-1P, Soffic.09G0015410-2T, Soffic.09G0016460-1T, Soffic.09G0016460-1P, Soffic.09G0017080-3C, Soffic.09G0018730-3P, Soffic.09G0018730-3C, Soffic.09G0019920-3C and Soffic.03G0019710-2C) were significantly different between resistant and susceptible progenies, indicating their key roles in sugarcane resistance to SCMV and SrMV infection. The seven QTLs and nine genes can provide a certain scientific reference to help sugarcane breeders develop varieties resistant to mosaic diseases.

Mapping of QTLs and Screening Candidate Genes Associated with the Ability of Sugarcane Tillering and Ratooning.

The processes of sugarcane tillering and ratooning, which directly affect the yield of plant cane and ratoon, are of vital importance to the population establishment and the effective stalk number per unit area. In the present study, the phenotypic data of 285 F1 progenies from a cross of sugarcane varieties YT93-159 × ROC22 were collected in eight environments, which consisted of plant cane and ratoon cultivated in three different ecological sites. The broad sense heritability (H2) of the tillering and the ratoon sprouting was 0.64 and 0.63, respectively, indicating that they were middle to middle-high heritable traits, and there is a significantly positive correlation between the two traits. Furthermore, a total of 26 quantitative trait loci (QTLs) related to the tillering ability and 11 QTLs associated with the ratooning ability were mapped on two high-quality genetic maps derived from a 100K SNP chip, and their phenotypic variance explained (PVE) ranged from 4.27-25.70% and 6.20-13.54%, respectively. Among them, four consistent QTLs of qPCTR-R9, qPCTR-Y28, qPCTR-Y60/qRSR-Y60 and PCTR-Y8-1/qRSR-Y8 were mapped in two environments, of which, qPCTR-Y8-1/qRSR-Y8 had the PVEs of 11.90% in the plant cane and 7.88% in the ratoon. Furthermore, a total of 25 candidate genes were identified in the interval of the above four consistent QTLs and four major QTLs of qPCTR-Y8-1, qPCTR-Y8-2, qRSR-R51 and qRSR-Y43-2, with the PVEs from 11.73-25.70%. All these genes were associated with tillering, including eight transcription factors (TFs), while 15 of them were associated with ratooning, of which there were five TFs. These QTLs and genes can provide a scientific reference for genetic improvement of tillering and ratooning traits in sugarcane.

Genome-wide characterization of sugarcane catalase gene family identifies a ScCAT1 gene associated disease resistance.

In plants, catalase (CAT) mainly scavenges H2O2 from reactive oxygen species (ROS) and regulates the growth and development. So far, genome-wide identification of CAT gene family in Saccharum has not yet been reported. Here, 16 SsCAT genes were identified based on a Saccharum spontaneum genome. They were clustered into three subfamilies, with closer genes sharing similar structures. Most SsCAT proteins contained three conserved amino acids, one active catalytic site, one heme-ligand signature, and three peroxisomal targeting signal 1 (PTS1) sequences. The cis-regulatory element prediction revealed that SsCAT genes were involved in growth and development, and in response to various hormones and stresses. RNA-Seq databases showed that SsCAT genes were differentially expressed in Saccharum tissues and under cold, drought, and Sporisorium scitamineum stresses. The ScCAT1 gene transcript (GenBank accession number KF664183) and relevant CAT activity were up-regulated under S. scitamineum stress. Overexpression of ScCAT1 gene in Nicotiana benthamiana could enhance its resistance to pathogen infection through scavenging of excessive toxic ROS and up-regulated expressions of genes related to hypersensitive response (HR), ROS and salicylic acid (SA) pathways. This study provides comprehensive information for the CAT gene family and sets up a basis for its function identification in sugarcane.

Ectopic Expression of Sugarcane ScAMT1.1 Has the Potential to Improve Ammonium Assimilation and Grain Yield in Transgenic Rice under Low Nitrogen Stress.

In China, nitrogen (N) fertilizer is excessively used in sugarcane planting areas, while the nitrogen use efficiency (NUE) of sugarcane is relatively low. Mining and identifying the key genes in response to low N stress in sugarcane can provide useful gene elements and a theoretical basis for developing sugarcane varieties with high NUE. In our study, RNA-Seq combined with qRT-PCR analysis revealed that the ScAMT1.1 gene responded positively to low N stress, resulting in the stronger low N tolerance and high NUE ability of sugarcane cultivar ROC22. Then, ScAMT1.1 was cloned from sugarcane. The full-length cDNA of the ScAMT1.1 gene is 1868 bp, containing a 1491 bp open reading frame (ORF), and encoding 496 amino acids. ScAMT1.1 belongs to the AMT superfamily and shares 91.57% homologies with AMT1.1 from Oryza sativa. Furthermore, it was stably overexpressed in rice (O. sativa). Under low N treatment, the plant height and the fresh weight of the ScAMT1.1-overexpressed transgenic rice were 36.48% and 51.55% higher than that of the wild-type, respectively. Both the activity of ammonium assimilation key enzymes GS and GDH, and the expression level of ammonium assimilation key genes, including GS1.1, GS1.2, GDH, Fd-GOGAT, and NADH-GOGAT2 in the transgenic plants, were significantly higher than that of the wild-type. The grain number and grain yield per plant in the transgenic rice were 6.44% and 9.52% higher than that of the wild-type in the pot experiments, respectively. Taken together, the sugarcane ScAMT1.1 gene has the potential to improve ammonium assimilation ability and the yield of transgenic rice under low N fertilizer conditions. This study provided an important functional gene for improving sugarcane varieties with high NUE.

Identification and characterization of WAK gene family in Saccharum and the negative roles of ScWAK1 under the pathogen stress.

Wall-associated kinase (WAK) is widely involved in signal transduction, reproductive growth, responses to pathogen infection and metal ion stress in plants. In this study, 19, 12, and 37 SsWAK genes were identified in Saccharum spontaneum, Saccharum hybrid and Sorghum bicolor, respectively. Phylogenetic tree showed that they could be divided into three groups. These WAK genes contained multiple cis-acting elements related to stress, growth and hormone response. RNA-seq analysis demonstrated that SsWAK genes were constitutively expressed in different sugarcane tissues and involved in response to smut pathogen (Sporisorium scitamineum) stress. Additionally, ScWAK1 (GenBank Accession No. OP479864), was then isolated from sugarcane cultivar ROC22. It was highly expressed in leaves and roots and its expression could be induced under SA and MeJA stress. Besides, ScWAK1 was significantly downregulated in both smut-resistant and susceptible sugarcane cultivars in response to S. scitamineum infection. ScWAK1 was a membrane protein without self-activating activity. Furthermore, transient expression of ScWAK1 in Nicotiana benthamiana enhanced the susceptibility of tobacco to the inoculation of Ralstonia solanacearum and Fusarium solani var. coeruleum, suggesting its negative role in disease resistance. The present study reveals the origin, distribution and evolution of WAK gene family and provides potential gene resources for sugarcane molecular breeding.