Molecular characterisation of a DREB gene from Sophora moorcroftiana, an endemic species of plateau

Estimation of morphological variation in seed traits of Sophora moorcroftiana using digital image analysis

Sophora moorcroftiana is a leguminous plant endemic to the Qinghai-Tibet Plateau. It has excellent abiotic stress tolerance and is considered an ideal species for local ecological restoration. However, the lack of genetic diversity in the seed traits of S. moorcroftiana hinders its conservation and utilization on the plateau. Therefore, in this study, genotypic variation and phenotypic correlations were estimated for nine seed traits among 15 accessions of S. moorcroftiana over two years, 2014 and 2019, respectively from 15 sample points. All traits evaluated showed significant (P< 0.05) genotypic variation. In 2014, accession mean repeatability was high for seed perimeter, length, width, and thickness, and 100-seed weight. In 2019, mean repeatability for seed perimeter and thickness, and 100-seed weight were high. The estimates of mean repeatability for seed traits across the two years ranged from 0.382 for seed length to 0.781 for seed thickness. Pattern analysis showed that 100-seed weight was significantly positively correlated with traits such as seed perimeter, length, width, and thickness, and identified populations with breeding pool potential. In the biplot, principal components 1 and 2 explained 55.22% and 26.72% of the total variation in seed traits, respectively. These accessions could produce breeding populations for recurrent selection to develop S. moorcroftiana varieties suitable for restoring the fragile ecological environment of the Qinghai-Tibet Plateau.

Geographic population genetic structure and diversity of Sophora moorcroftiana based on genotyping-by-sequencing (GBS)

Sophora moorcroftiana is a perennial leguminous low shrub endemic to the Yarlung Zangbo River basin in Tibet with irreplaceable economic and ecological value. To determine the drivers of evolution in this species, 225 individuals belonging to 15 populations from different geographic locations were sampled, and population genetics was studied using high-throughput genotyping-by-sequencing (GBS). Based on genetic diversity analysis, phylogenetic analysis, principal component analysis, and structure analysis, 15 natural populations were clustered into the following five subgroups: subgroup I (Shigatse subgroup) was located in the upper reaches of the Yarlung Zangbo River with a relatively high level of population genetic variation (means for PIC, Shannon and PI were 0.173, 0.326 and 0.0000305, respectively), and gene flow within the subgroup was also high (mean value for Nm was 4.67). Subgroup II (including Pop 7 and Pop 8; means for PIC, Shannon and PI were 0.182, 0.345 and 0.0000321, respectively), located in the middle reaches of the Yarlung Zangbo River had relatively high levels of gene flow with the populations distributed in the upper and lower reaches. The Nm between subgroup II with subgroups I and III was 3.271 and 2.894, respectively. Considering all the genetic diversity indices Pop 8 had relatively high genetic diversity. Subgroup III (the remaining mixed subgroup of Lhasa and Shannan) was located in the middle reaches of the Yarlung Zangbo River and the means for PIC, Shannon and PI were 0.172, 0.324 and 0.0000303, respectively. Subgroup IV (Nyingchi subgroup), located in the lower reaches of the Yarlung Zangbo River basin, showed a further genetic distance from the other subgroups and the means for PIC, Shannon and PI were 0.147, 0.277 and 0.0000263, respectively. Subgroup V (Nyingchi Gongbu Jiangda subgroup), located in the upper reaches of the Niyang River, had the lowest level of genetic variation (means for PIC, Shannon and PI were 0.106, 0.198 and 0.0000187, respectively) and gene flow with other populations (mean value for Nm was 0.42). According to the comprehensive analysis, the S. moorcroftiana populations generally expanded from upstream to downstream and displayed a high level of genetic differentiation in the populations in the upper and lower reaches. There were high levels of gene exchange between the central populations with upstream and downstream populations, and wind-induced seed dispersal was an important factor in the formation of this gene exchange mode.

Completed plastome sequence of Sophora moorcroftiana, an endemic shrub to the Qinghai-Tibet Plateau, China

Sophora moorcroftiana, an endemic Fabaceae species occurred in the Qinghai-Tibet plateau, China, has important economic value in local. Its completed plastome sequence is 148,930 bp in size, and comprises a pair of inverted repeat (IR) regions of 23,787 bp each, a large single-copy region of 83,342 bp and a small single-copy region of 18,014 bp. The GC content of the plastome was 30.2%. A total of 124 genes were identified, comprising 80 protein-coding genes, 36 tRNA genes and eight rRNA genes. There are 94 unique genes, with 15 genes duplicated in the IR regions. Phylogenetic tree shows that plastome of S. moorcroftiana is most related to that of S. alopecuroides. This plastome would be helpful for the study of molecular mechanism of photosynthesis, sustainable conservation, genetic improvement of S. moorcroftiana.

Ectopic Expression of OsDREB1G, a Member of the OsDREB1 Subfamily, Confers Cold Stress Tolerance in Rice

Plants adapt to adverse environmental conditions through physiological responses, such as induction of the abscisic acid signaling pathway, stomatal regulation, and root elongation. Altered gene expression is a major molecular response to adverse environmental conditions in plants. Several transcription factors function as master switches to induce the expression of stress-tolerance genes. To find out a master regulator for the cold stress tolerance in rice, we focused on functionally identifying DREB subfamily which plays important roles in cold stress tolerance of plants. Here, we characterized OsDREB1G (LOC_Os02g45450), a functionally unidentified member of the DREB1 subgroup. OsDREB1G is specifically induced under cold stress conditions among several abiotic stresses examined. This gene is dominantly expressed in leaf sheath, blade, node, and root. Transgenic rice overexpressing this gene exhibited strong cold tolerance and growth retardation, like transgenic rice overexpressing other OsDREB1 genes. However, unlike these rice lines, transgenic rice overexpressing OsDREB1G did not exhibit significant increases in drought or salt tolerance. Cold-responsive genes were highly induced in transgenic rice overexpressing DREB1G compared to wild type. In addition, OsDREB1G overexpression directly induced the expression of a reporter gene fused to the promoters of cold-induced genes in rice protoplasts. Therefore, OsDREB1G is a typical CBF/DREB1 transcription factor that specifically functions in the cold stress response. Therefore, OsDREB1G could be useful for developing transgenic rice with enhanced cold-stress tolerance.

Virus-Induced Gene Silencing (VIGS) in Aegilops tauschii and Its Use in Functional Analysis of AetDREB2

Among the available reverse genetic approaches for studying gene function, virus-induced gene silencing (VIGS) has several advantages. It allows rapid characterization of gene function independent of stable transformation, which is basically difficult to achieve in monocots, and offers the potential to silence individual or multiple genes of a gene family. In order to establish a VIGS system in Aegilops tauschii, modified vectors derived from Barley stripe mosaic virus (BSMV) were used for silencing a phytoene desaturase gene that provides a convenient visual reporter for silencing. The results demonstrated a high efficiency of BSMV-VIGS in A. tauschii. Moreover, the BSMV-VIGS system was used to target a 354 bp specific region of the Dehydration-responsive element-binding (AetDreb2) gene, resulting in successful silencing of the gene in A. tauschii plants, as verified by real-time qRT-PCR. Indeed, in comparison with plants that were inoculated with an empty vector (BSMV:00), a faster rate of wilting and a lower relative water content were observed in plants inoculated with BSMV:AetDreb2 when they were exposed to drought stress. Therefore, BSMV-VIGS can be efficiently employed as a novel tool for reverse genetics in A. tauschii. It can also be used to study the effects of polyploidization on the gene function by a comparative analysis between bread wheat and its diploid progenitor.

Expression of a populus histone deacetylase gene 84KHDA903 in tobacco enhances drought tolerance

Histone deacetylases (HDACs) play a key role in regulating plant growth, development and stress responses. However, functions of HDACs in woody plants are largely unknown. In this study, a novel gene encoding a RPD3/HDA1-type histone deacetylase was cloned from 84K poplar (Populus alba×Populus glandulosa) and designated as 84KHDA903. The 84KHDA903 encodes a protein composed of 500 amino acid residues, which contains a conserved HDAC domain. Transient expression of 84KHDA903 in onion epidermal cells suggested that it was exclusively localized in nucleus. The 84KHDA903 exhibited different expression patterns under drought, salt and ABA treatments. The expression of 84KHDA903 was responsive to drought and ABA but not to salt. To understand the function of 84KHDA903 in stress responses, the 84KHDA903 gene was transformed into tobacco. The expression of 84KHDA903 in tobacco increased the tolerance of transgenic seeds to mannitol but not to salt. In adult stage, the 84KHDA903-expressing tobacco exhibited drought tolerance and showed strong capacity to recover after drought. During the recovery period, the stress-responsive genes including NtDREB4, NtDREB3 and NtLEA5 were induced to be highly expressed in the 84KHDA903 transgenic plants in contrast to wild-type plants. Taken together, for the first time, we reported a RPD3/HDA1-type histone deacetylase from poplar, 84KHDA903, which acted as a positive regulator in drought stress responses.