Cytokinins are involved in the regulation of many plant growth and development processes, and function in response to abiotic stress. Cytokinin signaling is similar to the prokaryotic two-component signaling systems and includes the transcriptional upregulation of type-A response regulators (RRs), which in turn act to inhibit cytokinin signal response via negative feedback. Cytokinin signaling consists of several gene families and only a handful full of genes is studied. In this study, we demonstrated the function of two highly identical type-A RR genes from rice, OsRR9 and OsRR10, which are induced by cytokinin and only OsRR10 repressed by salinity stress in rice. Loss-of-function mutations give rise to mutant genes, osrr9/osrr10, which have higher salinity tolerance than wild type rice seedlings. The transcriptomic analysis uncovered several ion transporter genes, which were upregulated in response to salt stress in the osrr9/osrr10 mutants relative to the wild type seedlings. These include high-affinity potassium transporters, such as OsHKT1;1, OsHKT1;3 and OsHKT2;1, which play an important role in sodium and potassium homeostasis. In addition, disruption of the genes OsRR9 and OsRR10 also affects the expression of multiple genes related to photosynthesis, transcription and phytohormone signaling. Taken together, these results suggest that the genes OsRR9 and OsRR10 function as negative regulators in response to salinity in rice.
The rice landrace Horkuch, endemic to the southern saline coast of Bangladesh, is known to have salt tolerance traits and can therefore contribute to a high yielding recipient for breeding purposes. In this study, we reciprocally crossed Horkuch with high yielding but salt sensitive IR29 to detect the complement of genes that were responsible for conferring salt tolerance versus sensitivity at the seedling developmental stage. We looked at tolerant and sensitive F3families from individual F2segregating plants and analyzed them for differential gene expressions using RNAseq. In general, we observed higher numbers of genes differentially expressed in leaves compared to root tissues. This included both upregulation and downregulation of gene expression across our experimental factors. Gene expression decreased in sensitive leaf after stress exposure where tolerant plants showed the opposite trend. In root, tolerant plants expression decreased at higher time points of stress exposure. We also observed a strong maternal cytoplasmic effect on gene expression and this was most evident in roots where there was upregulation in functional enrichments related to phosphorylation, electron carriers, transporter and cation transmembrane activities. Stress groups (tolerant and sensitive) response in F3families were distinctive in both cytoplasmic backgrounds and involved uniquely upregulated genes in tolerant progenies including membrane sensor proteins, enzymes involved with signaling pathways, such as those producing trehalose and G-protein coupled receptor proteins, photosynthesis-related enzymes and golgi body recycling as well as prolamin precursor proteins involved in refolding of proteins. On the other hand, sensitivity was found to be associated with differential upregulation of only a few redox proteins and higher number of apoptosis related genes compared to the tolerant response. Overall, our highly replicated experimental design was powerful and allowed the detection of relatively subtle differential expression. Our future goal is to correlate these expression differences with QTLs in this population, which would help identify the relative importance of specific genetic loci and provide a direct avenue for combining higher levels of salt tolerance with better agronomic traits in rice.
more » « less- NSF-PAR ID:
- 10154135
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Scientific Reports
- Volume:
- 9
- Issue:
- 1
- ISSN:
- 2045-2322
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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SUMMARY Cytokinin has strong connections to development and a growing role in the abiotic stress response. Here we show that CYTOKININ RESPONSE FACTOR 2 (CRF2) is additionally involved in the salt (NaCl) stress response. CRF2 promoter‐GUS expression indicates CRF2 involvement in the response to salt stress as well as the previously known cytokinin response. Interestingly, CRF2 mutant seedlings are quite similar to the wild type (WT) under non‐stressed conditions yet have many distinct changes in response to salt stress. Cytokinin levels measured by liquid chromatography–tandem mass spectrometry (LC‐MS/MS) that increased in the WT after salt stress are decreased in
crf2 , potentially from CRF2 regulation of cytokinin biosynthesis genes. Ion content measured by inductively coupled plasma optical emission spectrometry (ICP‐OES) was increased in the WT for Na, K, Mn, Ca and Mg after salt stress, whereas the corresponding Ca and Mg increases are lacking incrf2 . Many genes examined by RNA‐seq analysis were altered transcriptionally by salt stress in both the WT andcrf2 , yet interestingly approximately one‐third of salt‐modifiedcrf2 transcripts (2655) showed unique regulation. Different transcript profiles for salt stress incrf2 compared with the WT background was further supported through an examination of co‐expressed genes by weighted gene correlation network analysis (WGCMA) and principal component analysis (PCA). Additionally, Gene Ontology (GO) enrichment terms found from salt‐treated transcripts revealed most photosynthesis‐related terms as only being affected incrf2 , leading to an examination of chlorophyll levels and the efficiency of photosystem II (via the ratio of variable fluorescence to maximum fluorescence,F v/F m) as well as physiology after salt treatment. Salt stress‐treatedcrf2 plants had both reduced chlorophyll levels and lowerF v/F mvalues compared with the WT, suggesting that CRF2 plays a role in the modulation of salt stress responses linked to photosynthesis.
