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Mosses are one of the earliest diverging land plants that adapted to living on land. The BURP domain-containing proteins (BURP proteins) are plant-specific proteins that appeared when plants shifted from aquatic environments to land. Phylogenetic analysis revealed that the BURP domain of higher plants is originated from lower land plants and divergent because of motif conversion. To discover the function of BURP protein in moss, rice transgenics with ectopic expression of PpBURP2 were subjected to different abiotic stresses treatments. The results revealed that the ectopic expression of PpBURP2 enhanced the tolerance to osmotic and saline stresses at the seedling stage and drought stress at the adult stage. Further ectopic expression of PpBURP2 improved the cadmium (2+) (Cd2+) tolerance and reduced Cd2+ accumulation in rice leaves. Transcriptomic analysis of the transgenic PpBURP2 plants showed that the differentially expressed genes were involved in the metabolism of secondary metabolites, energy, oxidation-reduction process, and defense-related genes. Further experiments showed that the photosynthetic efficiency and resistance against bacterial leaf blight were obviously improved in transgenic plants. Yeast two-hybrid and bimolecular fluorescence complementation (BiFC) assays revealed the physical interaction of BURP domain protein from rice and moss with mitogen-activated protein kinase kinase (MKK) from rice. Therefore, our findings demonstrate that overexpressing PpBURP2 in rice confers resistance to abiotic stresses and bacterial leaf blight. They also suggested that the regulatory role of BURP-like proteins across lower and higher plants was evolutionary conservation of responses of different classes of plants to different environmental challenges.

Drought stress adversely affects crop growth and productivity worldwide. In response, plants have evolved several strategies in which numerous genes are induced to counter stress. High mobility group (HMG) proteins are the second most abundant family of chromosomal proteins. They play a crucial role in gene transcriptional regulation by modulating the chromatin/DNA structure. In this study, we isolated a novel HMG gene, OsHMGB707, one of the candidate genes localized in the quantitative trait loci (QTL) interval of rice drought tolerance, and examined its function on rice stress tolerance. The expression of OsHMGB707 was up-regulated by dehydration and high salt treatment. Its overexpression significantly enhanced drought tolerance in transgenic rice plants, whereas its knockdown through RNA interference (RNAi) did not affect the drought tolerance of the transgenic rice plants. Notably, OsHMGB707-GFP is localized in the cell nucleus, and OsHMGB707 is protein-bound to the synthetic four-way junction DNA. Several genes were up-regulated in OsHMGB707-overexpression (OE) rice lines compared to the wild-type rice varieties. Some of the genes encode stress-related proteins (e.g., DREB transcription factors, heat shock protein 20, and heat shock protein DnaJ). In summary, OsHMGB707 encodes a stress-responsive high mobility group protein and regulates rice drought tolerance by promoting the expression of stress-related genes.

Water deficit caused a serious threat to crops, especially panicle development at reproductive growth phase. We investigated grain yield components and gene expression profiles of panicle among tolerant and sensitive rice in response to drought stress. Panicle morphologies exhibited that secondary branches per panicle were more severely affected as compared to primary branches per panicle. Moreover, grain weight per panicle showed significant decrease for both tolerant and sensitive varieties except for MILT1444. Expression profile analysis revealed that 783 differentially expressed genes (DEGs) were identified to be drought-induced from young panicles in 2 cm length. Hierarchical clustering indicated that 76.8% of DEGs were up-regulated for all six rice varieties, and the percentage of down-regulated genes was higher in sensitive group than tolerant group. Biological process category revealed that the shared Gene Ontology (GO) terms were involved in response to abiotic stimulus and stress, whereas the specific GO terms in tolerant group were identified as regulation of biological quality, homeostatic process, cell growth, anatomical structure morphogenesis and development, and the unique terms in sensitive varieties were identified as lipid metabolic process and secondary metabolic process. Furthermore, the gene-based association analysis narrowed down list of DEGs, and four genes common to all six varieties were selected as candidate for breeders. Together, we found several shared and distinct biological processes between tolerant and sensitive varieties, and candidate stress-responsive genes. These findings provided insight into functional mechanisms regulating drought stress response in panicle development and may also help to crop tolerant improvement. [ABSTRACT FROM AUTHOR]