Lilium pumilum stress-responsive NAC transcription factor LpNAC17 enhances salt stress tolerance in tobacco

WRKY Transcriptional Factor IlWRKY70 from Iris laevigata Enhances Drought and Salinity Tolerances in Nicotiana tabacum

Drought and high salinity greatly affect plant growth and development. WRKY transcription factors play a key role in plant tolerance to abiotic stress, but the functions of WRKYs in the ornamental monocotyledon Iris laevigata remain largely unexplored. In this study, we cloned IlWRKY70 and found that it is a Group III WRKY localized in the nucleus. The expression of IlWRKY70 was induced by NaCl and PEG-6000, which reached peaks (4.38 and 5.65 times) after 3 h and 1 h, respectively. The exogenous overexpression of IlWRKY70 in N. tabacum significantly improved the resistance under NaCl and drought treatments, as evidenced by higher germination rates, longer root lengths, and increased fresh weights compared to those of control plants. In addition, transgenic seedlings showed significantly reduced wilting, higher photosynthetic performance, higher Fv/Fm and chlorophyll content, and lower stomatal conductance. Moreover, transgenic lines showed higher antioxidant enzymatic activities, lower reactive oxygen species (ROS), and lower malondialdehyde contents. Accordingly, we also found higher expressions of antioxidant defense genes, including SOD, CAT, and POD, in transgenic lines compared to controls under salt and drought stresses. Thus, IlWRKY70 enhances the abilities of salt and drought tolerances in plants, at least partially, via ROS regulation and can be used for breeding I. laevigata possessing enhanced salt and drought resistances.

Genome-Wide Investigation of the NAC Transcription Factor Family in Apocynum venetum Revealed Their Synergistic Roles in Abiotic Stress Response and Trehalose Metabolism

NAC (NAM, ATAF1/2, and CUC2) transcription factors (TFs) are one of the most prominent plant-specific TF families and play essential roles in plant growth, development and adaptation to abiotic stress. Although the NAC gene family has been extensively characterized in many species, systematic analysis is still relatively lacking in Apocynum venetum (A. venetum). In this study, 74 AvNAC proteins were identified from the A. venetum genome and were classified into 16 subgroups. This classification was consistently supported by their gene structures, conserved motifs and subcellular localizations. Nucleotide substitution analysis (Ka/Ks) showed the AvNACs to be under the influence of strong purifying selection, and segmental duplication events were found to play the dominant roles in the AvNAC TF family expansion. Cis-elements analysis demonstrated that the light-, stress-, and phytohormone-responsive elements being dominant in the AvNAC promoters, and potential TFs including Dof, BBR-BPC, ERF and MIKC_MADS were visualized in the TF regulatory network. Among these AvNACs, AvNAC58 and AvNAC69 exhibited significant differential expression in response to drought and salt stresses. The protein interaction prediction further confirmed their potential roles in the trehalose metabolism pathway with respect to drought and salt resistance. This study provides a reference for further understanding the functional characteristics of NAC genes in the stress-response mechanism and development of A. venetum.

Transcriptome profiling revealed salt stress-responsive genes in Lilium pumilum bulbs

Lilium pumilum is an important ornamental, culinary and medicinal bulbous plants with salt tolerance. However, salt tolerance of lily, particularly the bulb, has been studied relatively little, which brings challenges to the cultivation of lily varieties with high salt tolerance. Here, we performed transcriptome sequencing on the bulb organs of L. pumilum under salt stress treatment, analyzed differential gene expressed levels and then identified several key genes associated with salt stress tolerance at genome-wide scale. For the first time, we revealed the obvious response against salt stress for L. pumilum bulb organs, while distinct from those for root organs. Several key genes obtained through transcriptome analysis and DEG screening include NF-YB3 transcription factor, metallothionein type 2 protein, vicilin like seed storage protein and bidirectional sugar transporter SWEET14. Rather than typical ROS scavengers like superoxide dismutase, peroxidase, and glutathione transferase, non-typical ROS scavengers such as the metallothionein type 2 protein, and vicilin like seed storage protein were upregulated in our work. The bidirectional sugar transporter SWEET14 protein and the hormone signaling proteins such as E3-ubiquitin protein ligases, PYL4 and protein phosphatase 2C were also upregulated, suggesting the role of sugars and hormones in the bulb organ responses to salt stress. Co-expression analysis of the DEGs further confirmed that NF-YB3 transcription factor acted as a hub gene, suggesting that salt stress can promote flowering of L. pumilum. Taken together, we identified important candidate genes associated with salt tolerance of the L. pumilum bulb organs, which may provide the excellent basis for further in-depth salt tolerance mechanisms of the lily bulbs.