Positive regulatory role of strigolactone in plant responses to drought and salt stress.

This report provides direct evidence that strigolactone (SL) positively regulates drought and high salinity responses in Arabidopsis. Both SL-deficient and SL-response [more axillary growth (max)] mutants exhibited hypersensitivity to drought and salt stress, which was associated with shoot- rather than root-related traits. Exogenous SL treatment rescued the drought-sensitive phenotype of the SL-deficient mutants but not of the SL-response mutant, and enhanced drought tolerance of WT plants, confirming the role of SL as a positive regulator in stress response. In agreement with the drought-sensitive phenotype, max mutants exhibited increased leaf stomatal density relative to WT and slower abscisic acid (ABA)-induced stomatal closure. Compared with WT, the max mutants exhibited increased leaf water loss rate during dehydration and decreased ABA responsiveness during germination and postgermination. Collectively, these results indicate that cross-talk between SL and ABA plays an important role in integrating stress signals to regulate stomatal development and function. Additionally, a comparative microarray analysis of the leaves of the SL-response max2 mutant and WT plants under normal and dehydrative conditions revealed an SL-mediated network controlling plant responses to stress via many stress- and/or ABA-responsive and cytokinin metabolism-related genes. Our results demonstrate that plants integrate multiple hormone-response pathways for adaptation to environmental stress. Based on our results, genetic modulation of SL content/response could be applied as a potential approach to reduce the negative impact of abiotic stress on crop productivity.

Characterization of the newly developed soybean cultivar DT2008 in relation to the model variety W82 reveals a new genetic resource for comparative and functional genomics for improved drought tolerance.

Soybean (Glycine max) productivity is adversely affected by drought stress worldwide, including Vietnam. In the last few years, we have made a great effort in the development of drought-tolerant soybean cultivars by breeding and/or radiation-induced mutagenesis. One of the newly developed cultivars, the DT2008, showed enhanced drought tolerance and stable yield in the field conditions. The purpose of this study was to compare the drought-tolerant phenotype of DT2008 and Williams 82 (W82) by assessing their water loss and growth rate under dehydration and/or drought stress conditions as a means to provide genetic resources for further comparative and functional genomics. We found that DT2008 had reduced water loss under both dehydration and drought stresses in comparison with W82. The examination of root and shoot growths of DT2008 and W82 under both normal and drought conditions indicated that DT2008 maintains a better shoot and root growth rates than W82 under both two growth conditions. These results together suggest that DT2008 has better drought tolerance degree than W82. Our results open the way for further comparison of DT2008 and W82 at molecular levels by advanced omic approaches to identify mutation(s) involved in the enhancement of drought tolerance of DT2008, contributing to our understanding of drought tolerance mechanisms in soybean. Mutation(s) identified are potential candidates for genetic engineering of elite soybean varieties to improve drought tolerance and biomass.

The auxin response factor transcription factor family in soybean: genome-wide identification and expression analyses during development and water stress.

In plants, the auxin response factor (ARF) transcription factors play important roles in regulating diverse biological processes, including development, growth, cell division and responses to environmental stimuli. An exhaustive search of soybean genome revealed 51 GmARFs, many of which were formed by genome duplications. The typical GmARFs (43 members) contain a DNA-binding domain, an ARF domain and an auxin/indole acetic acid (AUX/IAA) dimerization domain, whereas the remaining eight members lack the dimerization domain. Phylogenetic analysis of the ARFs from soybean and Arabidopsis revealed both similarity and divergence between the two ARF families, as well as enabled us to predict the functions of the GmARFs. Using quantitative real-time polymerase chain reaction (qRT-PCR) and available soybean Affymetrix array and Illumina transcriptome sequence data, a comprehensive expression atlas of GmARF genes was obtained in various organs and tissues, providing useful information about their involvement in defining the precise nature of individual tissues. Furthermore, expression profiling using qRT-PCR and microarray data revealed many water stress-responsive GmARFs in soybean, albeit with different patterns depending on types of tissues and/or developmental stages. Our systematic analysis has identified excellent tissue-specific and/or stress-responsive candidate GmARF genes for in-depth in planta functional analyses, which would lead to potential applications in the development of genetically modified soybean cultivars with enhanced drought tolerance.