Genome-wide investigation of the ZF-HD gene family in two varieties of alfalfa (Medicago sativa L.) and its expression pattern under alkaline stress

Molecular characterization of cassava zinc finger-homeodomain (ZF-HD) transcription factors reveals their role in disease resistance

The production of cassava (Manihot esculenta Crantz) is constantly threatened by cassava bacterial blight (CBB), caused by Xanthomonas phaseoli pv. manihotis (Xpm). Zinc finger-homeodomain (ZF-HD) belongs to a family of homozygous heterotypic cassette genes widely implicated in various developmental and physiological processes in plants. Despite their importance, a comprehensive analysis of ZF-HD genes, particularly those involved in disease resistance, has not been performed for cassava. In the present study, we utilized bioinformatics methods to identify 21 ZF-HD genes distributed across 11 chromosomes of cassava genome, with the majority exhibiting gene structure without introns. Phylogenetic analysis categorized these genes into two major groups (MIF and ZHD) with five subgroups. We observed fourteen pairs of duplicated genes, suggesting that segmental duplication has likely facilitated the expansion of the cassava ZF-HD gene family. Comparative orthologous analyses between cassava and other plant species shed light on the evolutionary trajectory of this gene family. Promoter analyses revealed multiple hormone- and stress-related elements, indicative of a functional role in stress responses. Expression profiling through RNA-seq and quantitative real-time PCR (qRT-PCR) demonstrated that certain cassava ZF-HD genes are up-regulated in response to Xpm infection, suggesting their involvement in defense mechanisms. Notably, MeZHD7 gene was identified via virus induced gene silencing (VIGS) as potentially crucial in conferring resistance against CBB. Results from subcellular localization experiments indicated that MeZHD7 was localized in the nucleus. The Luciferase reporter assay demonstrated an interaction between MeZHD7 and MeMIF5. These findings may lay the foundation for further cloning and functional analyses of cassava ZF-HD genes, particularly those associated with pathogen resistance.

NnSnRK1-NnATG1-mediated autophagic cell death governs flower bud abortion in shaded lotus

Many plants can terminate their flowering process in response to unfavourable environments, but the mechanisms underlying this response are poorly understood. In this study, we observed that the lotus flower buds were susceptible to abortion under shaded conditions. The primary cause of abortion was excessive autophagic cell death (ACD) in flower buds. Blockade of autophagic flux in lotus flower buds consistently resulted in low levels of ACD and improved flowering ability under shaded conditions. Further evidence highlights the importance of the NnSnRK1-NnATG1 signalling axis in inducing ACD in lotus flower buds and culminating in their timely abortion. Under shaded conditions, elevated levels of NnSnRK1 activated NnATG1, which subsequently led to the formation of numerous autophagosome structures in lotus flower bud cells. Excessive autophagy levels led to the bulk degradation of cellular material, which triggered ACD and the abortion of flower buds. NnSnRK1 does not act directly on NnATG1. Other components, including TOR (target of rapamycin), PI3K (phosphatidylinositol 3-kinase) and three previously unidentified genes, appeared to be pivotal for the interaction between NnSnRK1 and NnATG1. This study reveals the role of autophagy in regulating the abortion of lotus flower buds, which could improve reproductive success and act as an energy-efficient measure in plants.

Genome-wide identification and expression analysis of the ZF-HD gene family in pea (Pisum sativum L.)

Pea is a conventional grain-feed-grass crop in Tibet and the only high-protein legume in the region; therefore, it plays an important role in Tibetan food and grass security. Zinc finger-homeodomain (ZF-HD) belongs to a family of homozygous heterotypic cassette genes, which play an important role in plant growth, development, and response to adversity stress. Using a bioinformatics approach, 18 PsZF-HD family members were identified. These genes were distributed across seven chromosomes and two scaffold fragments, and evolutionary analysis classified them into two subgroups, MIF and ZHD. The MIF subgroup was subdivided into three subclasses (PsMIFⅠ-III), and the ZHD subgroup was subdivided into five subclasses (ZHDⅠ-V). The PsZF-HD members were named PsMIF1-PsMIF4 and PsZHD1-PsZHD14. Twelve conserved motifs and four conserved domains were identified from PsZF-HD family, of which MIF subgroup only contained one domain, while ZHD subgroup contained two types of domains. In addition, there were significant differences in the three-dimensional structures of the protein members of the two subgroups. Most PsZF-HD genes had no introns (13/18), and only five genes had one intron. Forty-five cis-acting elements were predicted and screened, involving four categories: light response, stress, hormone, and growth and development. Transcriptome analysis of different tissues during pea growth and development showed that PsZHD11, 8, 13, 14 and MIF4 were not expressed or were individually expressed in low amounts in the tissues, while the other 13 PsZF-HDs genes were differentially expressed and showed tissue preference, as seen in aboveground reproductive organs, where PsZHD6, 2, 10 and MIF1 (except immature seeds) were highly expressed. In the aerial vegetative organs, PsZHD6, 1, and 10 were significantly overexpressed, while in the underground root system, PsMIF3 was specifically overexpressed. The leaf transcriptome under a low-nitrogen environment showed that the expression levels of 17 PsZF-HDs members were upregulated in shoot organs. The leaf transcriptome analysis under a low-temperature environment showed stress-induced upregulation of PsZHD10 and one genes and down-regulation of PsZHD6 gene. These results laid the foundation for deeper exploration of the functions of the PsZF-HD genes and also improved the reference for molecular breeding for stress resistance in peas.

Genome-Wide Identification and Expression Analysis of HSF Transcription Factors in Alfalfa (Medicago sativa) under Abiotic Stress

Alfalfa (Medicago sativa) is one of the most important legume forage species in the world. It is often affected by several abiotic stressors that result in reduced yields and poor growth. Therefore, it is crucial to study the resistance of M. sativa to abiotic stresses. Heat shock transcription factors (HSF) are key players in a number of transcriptional regulatory pathways. These pathways play an essential role in controlling how plants react to different abiotic stressors. Studies on the HSF gene family have been reported in many species but have not yet undergone a thorough analysis in M. sativa. Therefore, in order to identify a more comprehensive set of HSF genes, from the genomic data, we identified 16 members of the MsHSF gene, which were unevenly distributed over six chromosomes. We also looked at their gene architectures and protein motifs, and phylogenetic analysis allowed us to divide them into 3 groups with a total of 15 subgroups. Along with these aspects, we then examined the physicochemical properties, subcellular localization, synteny analysis, GO annotation and enrichment, and protein interaction networks of amino acids. Finally, the analysis of 16 MsHSF genes' expression levels across all tissues and under four abiotic stresses using publicly available RNA-Seq data revealed that these genes had significant tissue-specific expression. Moreover, the expression of most MsHSF genes increased dramatically under abiotic stress, further validating the critical function played by the MsHSF gene family in abiotic stress. These results provided basic information about MsHSF gene family and laid a foundation for further study on the biological role of MsHSF gene in response to stress in M. sativa.

Physiological and transcriptomic analysis uncovers salinity stress mechanisms in a facultative crassulacean acid metabolism plant Dendrobium officinale

Dendrobium officinale is a precious medicinal Chinese herb that employs facultative crassulacean acid metabolism (CAM) and has a high degree of abiotic stress tolerance, but the molecular mechanism underlying the response of this orchid to abiotic stresses is poorly understood. In this study, we analyzed the root microstructure of D. officinale plantlets and verified the presence of chloroplasts by transmission electron microscopy. To obtain a more comprehensive overview of the molecular mechanism underlying their tolerance to abiotic stress, we performed whole-transcriptome sequencing of the roots of 10-month-old plantlets exposed to salt (NaCl) treatment in a time-course experiment (0, 4 and 12 h). The total of 7376 differentially expressed genes that were identified were grouped into three clusters (P < 0.05). Metabolic pathway analysis revealed that the expression of genes related to hormone (such as auxins, cytokinins, abscisic acid, ethylene and jasmonic acid) biosynthesis and response, as well as the expression of genes related to photosynthesis, amino acid and flavonoid metabolism, and the SOS pathway, were either up- or down-regulated after salt treatment. Additionally, we identified an up-regulated WRKY transcription factor, DoWRKY69, whose ectopic expression in Arabidopsis promoted seed germination under salt tress. Collectively, our findings provide a greater understanding of the salt stress response mechanisms in the roots of a facultative CAM plant. A number of candidate genes that were discovered may help plants to cope with salt stress when introduced via genetic engineering.