OsCKX2 regulates phosphate deficiency tolerance by modulating cytokinin in rice

Identification of CKX gene family in Morus indica cv K2 and functional characterization of MiCKX4 during abiotic stress

Cytokinin oxidase/dehydrogenase (CKX) is the key enzyme that has been observed to catalyze irreversible inactivation of cytokinins and thus modulate cytokinin levels in plants. CKX gene family is known to have few members which are, expanded in the genome mainly due to duplication events. A total of nine MiCKXs were identified in Morus indica cv K2 with almost similar gene structures and conserved motifs and domains. The cis-elements along with expression analysis of these MiCKXs revealed their contrasting and specific role in plant development across different developmental stages. The localization of these enzymes in ER and Golgi bodies signifies their functional specification and property of getting modified post-translationally to carry out their activities. The overexpression of MiCKX4, an ortholog of AtCKX4, displayed longer primary root and higher number of lateral roots. Under ABA stress also the transgenic lines showed higher number of lateral roots and tolerance against drought stress as compared to wild-type plants. In this study, the CKX gene family members were analyzed bioinformatically for their roles under abiotic stresses.

Comparative physiological and transcriptomic analysis of two salt-tolerant soybean germplasms response to low phosphorus stress: role of phosphorus uptake and antioxidant capacity

BACKGROUND

Phosphorus (P) and salt stress are common abiotic stressors that limit crop growth and development, but the response mechanism of soybean to low phosphorus (LP) and salt (S) combined stress remains unclear.

RESULTS

In this study, two soybean germplasms with similar salt tolerance but contrasting P-efficiency, A74 (salt-tolerant and P-efficient) and A6 (salt-tolerant and P-inefficient), were selected as materials. By combining physiochemical and transcriptional analysis, we aimed to elucidate the mechanism by which soybean maintains high P-efficiency under salt stress. In total, 14,075 differentially expressed genes were identified through pairwise comparison. PageMan analysis subsequently revealed several significantly enriched categories in the LP vs. control (CK) or low phosphorus + salt (LPS) vs. S comparative combination when compared to A6, in the case of A74. These categories included genes involved in mitochondrial electron transport, secondary metabolism, stress, misc, transcription factors and transport. Additionally, weighted correlation network analysis identified two modules that were highly correlated with acid phosphatase and antioxidant enzyme activity. Citrate synthase gene (CS), acyl-coenzyme A oxidase4 gene (ACX), cytokinin dehydrogenase 7 gene (CKXs), and two-component response regulator ARR2 gene (ARR2) were identified as the most central hub genes in these two modules.

CONCLUSION

In summary, we have pinpointed the gene categories responsible for the LP response variations between the two salt-tolerant germplasms, which are mainly related to antioxidant, and P uptake process. Further, the discovery of the hub genes layed the foundation for further exploration of the molecular mechanism of salt-tolerant and P-efficient in soybean.

Evaluation of Differentially Expressed Genes in Leaves vs. Roots Subjected to Drought Stress in Flax (Linum usitatissimum L.)

Drought stress is a common environmental challenge that plants face, severely constraining plant growth and reducing crop yield and quality. Several studies have highlighted distinct responses between monocotyledonous and dicotyledonous plants. However, the mechanisms underlying flax tolerance to abiotic stress, such as drought, remain unclear. In this study, we investigated the morphological, physiological, and biochemical characteristics and the genome-wide gene expression of oil flax and fiber flax in response to drought stress. The results revealed that drought stress caused significant wilting of flax leaves. Within the first 24 h of stress, various physiological and biochemical characteristics exhibited rapid responses. These included fresh weight, relative water content (RWC), proline, soluble protein, soluble sugar, superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in the leaves or roots of flax. Additionally, drought stress led to a significant rise in lignin content in fiber flax. In addition, the transcriptome analysis demonstrated genome-wide variations in gene expression induced by drought stress. Specifically, genes associated with photosynthesis, proline biosynthesis, and phytohormone metabolism exhibited significant differences in expression levels under stress conditions in flax. These findings highlight the rapid response of flax to drought stress within a short-term period. Our experiment also revealed that, although there were variations in the levels of small compound content or gene expression between Longya10 and Fany under drought stress, most stress-resistance responses were similar. Furthermore, the results provide additional evidence supporting the existence of mechanisms underlying the response to drought stress in plants.

Loss-function mutants of OsCKX gene family based on CRISPR-Cas systems revealed their diversified roles in rice

Cytokinin (CTK) is an important plant hormone that promotes cell division, controls cell differentiation, and regulates a variety of plant growth and development processes. Cytokinin oxidase/dehydrogenase (CKX) is an irreversible cytokinin-degrading enzyme that affects plant growth and development by regulating the dynamic balance of CTKs synthesis and degradation. There are presumed 11 members of the CKX gene family in rice (Oryza sativa L.), but limited members have been reported. In this study, based on CRISPR-Cas9 and CRISPR-Cas12a genome-editing technology, we established a complete set of OsCKX1-OsCKX11 single-gene mutants, as well as double-gene and triple-gene mutants of different OsCKXs gene combinations with high similarity. The results revealed that CRISPR-Cas12a outperformed Cas9 to generate biallelic mutations, multi-gene mutants, and more diverse genotypes. And then, we found, except the reported OsCKX2, OsCKX4, OsCKX9 and OsCKX11, OsCKX5, OsCKX6, OsCKX7, and OsCKX8 also had significant effects on agronomic traits such as plant height, panicle size, grain size, and grain number per panicle in rice. In addition, the different loss-of-function of the OsCKX genes also changed the seed appearance quality and starch composition. Interestingly, by comparing different combinations of multi-gene mutants, we found significant functional redundancy among OsCKX gene members in the same phylogenetic clade. These data collectively reveal the diversified regulating capabilities of OsCKX genes in rice, and also provide the valuable reference for further rice molecular breeding.

Modifications of Phytohormone Metabolism Aimed at Stimulation of Plant Growth, Improving Their Productivity and Tolerance to Abiotic and Biotic Stress Factors

Due to the growing human population, the increase in crop yield is an important challenge for modern agriculture. As abiotic and biotic stresses cause severe losses in agriculture, it is also crucial to obtain varieties that are more tolerant to these factors. In the past, traditional breeding methods were used to obtain new varieties displaying demanded traits. Nowadays, genetic engineering is another available tool. An important direction of the research on genetically modified plants concerns the modification of phytohormone metabolism. This review summarizes the state-of-the-art research concerning the modulation of phytohormone content aimed at the stimulation of plant growth and the improvement of stress tolerance. It aims to provide a useful basis for developing new strategies for crop yield improvement by genetic engineering of phytohormone metabolism.