Exogenous Application Of Cytokinin Research Articles

Induced Water Deficit Tolerance in Hexaploid Wheat through Exogenous Application of Trehalose and Cytokinins: Water Relations and Physiological Changes

Induced Water Deficit Tolerance in Hexaploid Wheat through Exogenous Application of Trehalose and Cytokinins: Water Relations and Physiological Changes

Rice bundle sheath cell shape is regulated by the timing of light exposure during leaf development.

Plant leaves contain multiple cell types which achieve distinct characteristics whilst still coordinating development within the leaf. The bundle sheath possesses larger individual cells and lower chloroplast content than the adjacent mesophyll, but how this morphology is achieved remains unknown. To identify regulatory mechanisms determining bundle sheath cell morphology we tested the effects of perturbing environmental (light) and endogenous signals (hormones) during leaf development of Oryza sativa (rice). Total chloroplast area in bundle sheath cells was found to increase with cell size as in the mesophyll but did not maintain a 'set-point' relationship, with the longest bundle sheath cells demonstrating the lowest chloroplast content. Application of exogenous cytokinin and gibberellin significantly altered the relationship between cell size and chloroplast biosynthesis in the bundle sheath, increasing chloroplast content of the longest cells. Delayed exposure to light reduced the mean length of bundle sheath cells but increased corresponding leaf length, whereas premature light reduced final leaf length but did not affect bundle sheath cells. This suggests that the plant hormones cytokinin and gibberellin are regulators of the bundle sheath cell-chloroplast relationship and that final bundle sheath length may potentially be affected by light-mediated control of exit from the cell cycle.

Transcription factor FveMYB117a inhibits axillary bud outgrowth by regulating cytokinin homeostasis in woodland strawberry.

Shoot branching affects plant architecture. In strawberry (Fragaria L.), short branches (crowns) develop from dormant axillary buds to form inflorescences and flowers. While this developmental transition contributes greatly to perenniality and yield in strawberry, its regulatory mechanism remains unclear and understudied. In the woodland strawberry (Fragaria vesca), we identified and characterized two independent mutants showing more crowns. Both mutant alleles reside in FveMYB117a, a R2R3-MYB transcription factor gene highly expressed in shoot apical meristems, axillary buds and young leaves. Transcriptome analysis revealed that the expression of several cytokinin pathway genes was altered in the fvemyb117a mutant. Consistently, active cytokinins were significantly increased in the axillary buds of the fvemyb117a mutant. Exogenous application of cytokinin enhanced crown outgrowth in the wild type, whereas the cytokinin inhibitors suppressed crown outgrowth in the fvemyb117a mutant. FveMYB117a binds directly to the promoters of the cytokinin homeostasis genes FveIPT2 encoding an isopentenyltransferase and FveCKX1 encoding a cytokinin oxidase to regulate their expression. Conversely, the type-B Arabidopsis response regulators FveARR1 and FveARR2b can directly inhibit the expression of FveMYB117a, indicative of a negative feedback regulation. In conclusion, we identified FveMYB117a as a key repressor of crown outgrowth by inhibiting cytokinin accumulation and provide a mechanistic basis for bud fate transition in an herbaceous perennial plant.

OsRR26, a type-B response regulator, modulates salinity tolerance in rice via phytohormone-mediated ROS accumulation in roots and influencing reproductive development.

OsRR26 is a cytokinin-responsive response regulator that promotes phytohormone-mediated ROS accumulation in rice roots, regulates seedling growth, spikelet fertility, awn development, represses NADPH oxidases, and negatively affects salinity tolerance. Plant two-component systems (TCS) play a pivotal role in phytohormone signaling, stress responses, and circadian rhythm. However, a significant knowledge gap exists regarding TCS in rice. In this study, we utilized a functional genomics approach to elucidate the role of OsRR26, a type-B response regulator in rice. Our results demonstrate that OsRR26 is responsive to cytokinin, ABA, and salinity stress, serving as the ortholog of Arabidopsis ARR11. OsRR26 primarily localizes to the nucleus and plays a crucial role in seedling growth, spikelet fertility, and the suppression of awn development. Exogenous application of cytokinin led to distinct patterns of reactive oxygen species (ROS) accumulation in the roots of both WT and transgenic plants (OsRR26OE and OsRR26KD), indicating the potential involvement of OsRR26 in cytokinin-mediated ROS signaling in roots. The application of exogenous ABA resulted in varied cellular compartmentalization of ROS between the WT and transgenic lines. Stress tolerance assays of these plants revealed that OsRR26 functions as a negative regulator of salinity stress tolerance across different developmental stages in rice. Physiological and biochemical analyses unveiled that the knockdown of OsRR26 enhances salinity tolerance, characterized by improved chlorophyll retention and the accumulation of soluble sugars, K+ content, and amino acids, particularly proline.

Response of Bread Wheat Cultivars to Terminal Water Stress and Cytokinin Application from a Grain Phenotyping Perspective

A better understanding of the responsiveness of grain phenotypic indices to terminal water stress (TWS) in wheat might help explain grain weight variations and determine which grain traits are most affected. A two-year field experiment (2020–2021 and 2021–2022) was conducted to identify how TWS and exogenous cytokinin application might affect grain weight and grain dimensions in three bread wheat cultivars using high-throughput digital image phenotyping. The results showed that the effects of growing seasons, irrigation, and cultivars were significant on grain weight and phenotypic indices. In our study, TWS significantly reduced thousand grain weight (24.62%, 14.65%) and grain development in the width directions MinFeret, i.e., minimum caliper diameter (10.70%, 6.64%) and Minor, i.e., the minor axes of the best fitted ellipses to the grains (10.91%, 6.65%), or synthesized indices including Area/Perim. (9.01%, 5.42%), Area × Circ. (17.30%, 10.13%), Minor/Solid. (10.26%, 6.32%), MinFeret/Solid. (10.01%, 6.11%), Area × Solid (13.94%, 7.96%), Perim. × Circ. (9.07%, 5.42%), A1 (29.99%, 17.09%), and A2 (30.20%, 17.27%) in each growing season, respectively. Regardless of the factors causing these variations, a sustained relationship was found between thousand grain weight and phenotypic indices, with significant positive correlations. The stronger positive correlation between thousand grain weight and grain width indices (r ≥ 0.965) showed important implications for grain development and filling. The Torabi cultivar performed better than the Sirvan and Pishgam in both growing season conditions. In addition, the technical advantages of developing phenotyping approaches, the present study could contribute to a better physiological evaluation of wheat cultivars in multivariate environments.

Petal size is controlled by the MYB73/TPL/HDA19-miR159-CKX6 module regulating cytokinin catabolism in Rosa hybrida

The size of plant lateral organs is determined by well-coordinated cell proliferation and cell expansion. Here, we report that miR159, an evolutionarily conserved microRNA, plays an essential role in regulating cell division in rose (Rosa hybrida) petals by modulating cytokinin catabolism. We uncover that Cytokinin Oxidase/Dehydrogenase6 (CKX6) is a target of miR159 in petals. Knocking down miR159 levels results in the accumulation of CKX6 transcripts and earlier cytokinin clearance, leading to a shortened cell division period and smaller petals. Conversely, knocking down CKX6 causes cytokinin accumulation and a prolonged developmental cell division period, mimicking the effects of exogenous cytokinin application. MYB73, a R2R3-type MYB transcription repressor, recruits a co-repressor (TOPLESS) and a histone deacetylase (HDA19) to form a suppression complex, which regulates MIR159 expression by modulating histone H3 lysine 9 acetylation levels at the MIR159 promoter. Our work sheds light on mechanisms for ensuring the correct timing of the exit from the cell division phase and thus organ size regulation by controlling cytokinin catabolism.

Response of sugarcane plants with modified cytokinin homeostasis under water deficit conditions

Cytokinins (CK) are one of the main phytohormones involved in plant growth and development and play a role in plant adaptation to stress. In this study, the response to water deficit stress was investigated in sugarcane (Saccharum spp. hybrids) plants after exogenous application of CK and partial silencing of endogenous cytokinin oxidase/dehydrogenase (CKX) gene expression in transgenic plants. The CKX enzyme is responsible for CK breakdown in plant cells. A foliar drench of N6-benzyladenin on leaves (100 μM) resulted in plants that survived more than 10 days of water deficit stress compared with the untreated control plants, which displayed senescence and leaf wilting after 10 days without water. Furthermore, after 10 days without water, the treated plants maintained a high efficiency of the photosystem II (PSII) and displayed higher levels of chlorophyll and relative water content, and after 20 days without water, high catalase activity and proline content when compared with the untreated controls. In addition, sugarcane calli were transformed with a recombinant vector containing a 237 bp sugarcane ShCKX target sequence which included a conserved CK binding domain cloned in sense and antisense orientations. Partial silencing of CKX expression in the transgenic plants resulted in significantly lower salicylic acid levels after 21 days of deficit stress compared with untransformed controls. Stressed transgenic plants accumulated less H2O2, more antioxidants (superoxide dismutase and catalase) and proline when compared with the wild type (WT) plants. Moreover, the transgenic plants were able to retain high levels of chlorophyll and most maintained the efficiency of PSII after watering was stopped. The transgenic genotype with the highest level of CKX silencing displayed delayed leaf senescence and maintained high leaf water content under water deficit stress compared with the WT plants. Both the exogenous application of CK and the partial silencing of CKX expression enabled the plants to resprout after re-watering following the stress period. The results indicate that the manipulation of CK levels, either by increasing CK exogenously or deceasing their break down by partial silencing of the CKX gene, in sugarcane positively affects the response to water deficit stress through a variety of physiological mechanisms.

Phytohormonal impacts on fatty acid profiles in Chlorella vulgaris Beijerinck: endogenous identification and exogenous application of cytokinins and abscisic acid

Phytohormonal impacts on fatty acid profiles in Chlorella vulgaris Beijerinck: endogenous identification and exogenous application of cytokinins and abscisic acid

Application of exogenous cytokinin regulates cytokinin oxidase and antioxidant activity to maintain chlorophyll pigment during ripening of banana fruit

Banana fruit ripening is accompanied by changes in activity of chlorophyll degradation. Herein, the application of exogenous cytokinin of forchlorfenuron (CPPU) to delay the ripening process by retarding degradation of chlorophyll was investigated. The changes in peel color, hue angle, chlorophyll fluorescence, and chlorophyll content were significantly inhibited by exogenous application of cytokinin. Content of endogenous cytokinin of t-zeatin was maintained and the increase of cytokinin oxidase (CKX) activity was retarded. Similar change trends were verified in the isolated peel tissues treated with CPPU. Relative expression level of the genes involved in cytokinin synthesis (MaIPT1/12) were upregulated, and CKX-related (MaCKX1/12) and chlorophyll degradation-related catabolism (MaPAO1, MaCLH1, MaSGR1, MaRCCR1, and MaRCCR12) were downregulated during storage. In addition, the scavenging activity of free radicals and membrane integrity were stabilized. Application of exogenous cytokinin of CPPU was proposed to competitively inhibit CKX activity to maintain endogenous cytokinin level, which further delayed chlorophyll degradation during banana fruit ripening.

Cloning and Functional Analysis of the VfRR17 Gene from tung tree (Vernicia fordii).

Tung tree (Vernicia fordii) is one of the four major woody oilseed species in China. However, its fruit yield is severely hampered by the low number of female flowers and the imbalanced male-to-female flower ratio, which is a problem that restricts the development of the oilseed industry. Previous research has demonstrated that the exogenous application of cytokinins can significantly augment the number of female flowers, although the underlying regulatory mechanism remains elusive. To elucidate the involvement of VfRR17, a member of the A-type ARRs family, in the exogenous cytokinin regulation of flower sexual differentiation in tung tree, this study conducted a comprehensive bioinformatic analysis of the physicochemical properties, structural characteristics, and evolutionary relationships of the protein encoded by VfRR17. Additionally, gene function analysis was performed using subcellular localization, qRT-PCR, and genetic transformation techniques. The findings revealed that the VfRR17 gene's coding region spanned 471 bp, encoding an unstable protein of 156 amino acids with a relative molecular mass of 17.4 kDa. Phylogenetic analysis demonstrated a higher similarity between VfRR17 of the tung tree and the RR17 gene of Jatropha curcas, Ricinus communis, Hevea brasiliensis, and other species within the Euphorbiaceae family compared to other species, with the greatest similarity of 86% observed with the RR17 gene of Jatropha curcas. The qRT-PCR analysis indicated that VfRR17 exhibited high expression levels during the early stage of tung tree inflorescence buds following 6-BA treatment, peaking at 24 h and displaying a 3.47-fold increase compared to that at 0 h. In female and male flowers of the tung tree, the expression in female flowers during the 1 DBF period was significantly higher than in male flowers, exhibiting a difference of approximately 47.91-fold. Furthermore, notable differential expression was observed in the root, leaf, and petiole segments of the tung tree under low-temperature stress at the 12-h time point. In transgenic Arabidopsis, the VfRR17 lines and wild-type lines exhibited significantly different flowering times under an exogenous 6-BA treatment at a concentration of 2 mg/L, with the VfRR17 lines experiencing an 11-day delay compared to the wild-type lines. Additionally, the number of fruit pods in VfRR17 transgenic Arabidopsis lines was significantly reduced by 28 compared to the wild-type lines at a 6-BA concentration of 3 mg/L. These findings suggest that VfRR17 likely plays a critical role in regulating flower development in response to exogenous 6-BA, providing valuable insights into the mechanisms underlying exogenous 6-BA-mediated regulation of female flower development in the tung tree.

Cytokinins act synergistically with heat acclimation to enhance rice thermotolerance affecting hormonal dynamics, gene expression and volatile emission

Heat stress is a frequent environmental constraint. Phytohormones can significantly affect plant thermotolerance. This study compares the effects of exogenous cytokinin meta-topolin-9-(tetrahydropyran-2-yl)purine (mT9THP) on rice (Oryza sativa) under control conditions, after acclimation by moderate temperature (A; 37 °C, 2h), heat stress (HS; 45 °C, 6h) and their combination (AHS). mT9THP is a stable cytokinin derivative that releases active meta-topolin gradually, preventing the rapid deactivation reported after exogenous cytokinin application. Under control conditions, mT9THP negatively affected jasmonic acid in leaves and abscisic and salicylic acids in crowns (meristematic tissue crucial for tillering). Exogenous cytokinin stimulated the emission of volatile organic compounds (VOC), especially 2,3-butanediol. Acclimation upregulated trans-zeatin, expression of stress- and hormone-related genes, and VOC emission. The combination of acclimation and mT9THP promoted the expression of stress markers and antioxidant enzymes and moderately increased VOC emission, including 2-ethylhexyl salicylate or furanones. AHS and HS responses shared some common features, namely, increase of ethylene precursor aminocyclopropane-1-carboxylic acid (ACC), cis-zeatin and cytokinin methylthio derivatives, as well as the expression of heat shock proteins, alternative oxidases, and superoxide dismutases. AHS specifically induced jasmonic acid and auxin indole-3-acetic acid levels, diacylglycerolipids with fewer double bonds, and VOC emissions [e.g., acetamide, lipoxygenase (LOX)-derived volatiles]. Under direct HS, exogenous cytokinin mimicked some positive acclimation effects. The combination of mT9THP and AHS had the strongest thermo-protective effect, including a strong stimulation of VOC emissions (including LOX-derived ones). These results demonstrate for the first time the crucial contribution of volatiles to the beneficial effects of cytokinin and AHS on rice thermotolerance.

Shoot differentiation from Dendrocalamus brandisii callus and the related physiological roles of sugar and hormones during shoot differentiation.

Only a few calli regeneration systems of bamboos were successfully established, which limited the research on the physiological mechanism of callus differentiation. In this study, we successfully established the callus differentiation systems of Dendrocalamus brandisii (Munro) via seeds. The results showed that the best medium for the callus induction of D. brandisii seeds was basal Murashige and Skoog (1962) (MS) media amended with 5.0mgl-1 2,4-D and 0.5mgl-1 kinetin (KT), and the optimal medium for shoot differentiation was the basal MS media supplemented with 4.0mgl-1 6-benzylaminopurine (6-BA) and 0.5mgl-1 1-Naphthaleneacetic acid (NAA). Callus tissues had apparent polarity in cell arrangement and developed their own meristematic cell layers. Alpha-amylase (α-amylase), starch phosphorylase (STP) and sucrose synthase (SUSY) played a dominant role in carbohydrate degradation in callus during shoot differentiation. The pentose phosphate pathway (PPP) and TCA pathways were up-regulated in the shoot-differentiated calli. The dynamics of 6-BA and KT contents in calli were consistent with their concentrations applied in medium. Indoleacetic acid (IAA) synthesis and the related signal transduction were down-regulated, whereas the endogenous CTK contents were up-regulated by the exogenous cytokinin (CTK) application in shoot-differentiated calli, and their related synthesis, transport and signal transduction pathways were also up-regulated. The down-regulated signal transduction pathways of IAA and abscisic acid (ABA) revealed that they did not play the key role in the shoot differentiation of bamboos. Gibberellins (GAs) also played a role in shoot differentiation based on the down-regulation of DELLA and the up-regulation of PIF4 genes. The overexpression of DbSNRK2 and DbFIF4 genes further confirmed the negative role of ABA and the positive role of GAs in shoot differentiation.

Absence of Arabidopsis Polyamine Oxidase 5 Influences the Cytokinin-Induced Shoot Meristem Formation from Lateral Root Primordia.

Lateral root primordia (LRPs) of Arabidopsis can be directly converted to shoot meristems (SMs) by the application of exogenous cytokinin. Here, we report that Arabidopsis POLYAMINE OXIDASE 5 (AtPAO5) contributes to this process, since the rate of SM formation from LRPs was significantly lower in the pao5-2 knockout mutant. Furthermore, the presented experiments showed that AtPAO5 influences SM formation via controlling the thermospermine (T-Spm) level. Gene expression analyses supported the view that the pao5-2 mutation as well as exogenous T-Spm downregulate the expression of the class 3 haemoglobin coding genes AtGLB1 and AtGLB2. AtGLB1 and 2 have been reported to augment cytokinin sensitivity, indirectly inhibiting the expression of type-A ARABIDOPSIS RESPONSE REGULATORs (ARRs). In agreement, the same ARR-coding genes were found to be upregulated in the pao5-2 mutant. Although GLB proteins might also control cytokinin-induced nitric oxide (NO) accumulation, we could not find experimental evidence for it. Rather, the negative effect of NO-donor treatment on AtPAO5 gene expression and SM formation was seen. Nevertheless, a hypothetical pathway is set up explaining how AtPAO5 may affect direct shoot meristem formation, controlling cytokinin sensitivity through T-Spm and GLBs.

Physiological interventions in induction of parthenocarpy with fruits and vegetables: A Review

Seedless fruits have gained importance in the present era of the Horticulture Industry. One of the scientific reasons behind that seedlessness is parthenocarpy i.e. production of fruits without pollination and fertilization. The processes of positive and negative signaling that occur after pollination and fertilization are fundamentally dependent on plant growth hormones. These hormones are necessary for the growth and development of seeds and fruit. Exogenous application of different concentrated plant growth regulators, particularly auxin, cytokinins, and gibberellins, or combinations of these, prior to floral induction can also result in seedless fruit. It has been documented in a number of fruit and vegetable crops, including cucumber, tomato, brinjal, apple, and pears. A tight control between these two growth hormones can be seen in the early phases of fruit development, where auxin application promotes gibberellin biosynthesis and gibberellin application increases auxin content. Synthetic cytokinins are applied to pre-anthesis ovaries to activate cell division, which leads to the production of parthenocarpic fruit.

RAV1 mediates cytokinin signaling for regulating primary root growth in Arabidopsis.

Root growth dynamics is an outcome of complex hormonal crosstalk. The primary root meristem size, for example, is determined by antagonizing actions of cytokinin and auxin. Here we show that RAV1, a member of the AP2/ERF family of transcription factors, mediates cytokinin signaling in roots to regulate meristem size. The rav1 mutants have prominently longer primary roots, with a meristem that is significantly enlarged and contains higher cell numbers, compared with wild-type. The mutant phenotype could be restored on exogenous cytokinin application or by inhibiting auxin transport. At the transcript level, primary cytokinin-responsive genes like ARR1, ARR12 were significantly downregulated in the mutant root, indicating impaired cytokinin signaling. In concurrence, cytokinin induced regulation of SHY2, an Aux/IAA gene, and auxin efflux carrier PIN1 was hindered in rav1, leading to altered auxin transport and distribution. This effectively altered root meristem size in the mutant. Notably, CRF1, another member of the AP2/ERF family implicated in cytokinin signaling, is transcriptionally repressed by RAV1 to promote cytokinin response in roots. Further associating RAV1 with cytokinin signaling, our results demonstrate that cytokinin upregulates RAV1 expression through ARR1, during post-embryonic root development. Regulation of RAV1 expression is a part of secondary cytokinin response that eventually represses CRF1 to augment cytokinin signaling. To conclude, RAV1 functions in a branch pathway downstream to ARR1 that regulates CRF1 expression to enhance cytokinin action during primary root development in Arabidopsis.

Exogenous methyl jasmonate and cytokinin antagonistically regulate lignin biosynthesis by mediating CsHCT expression in Camellia sinensis.

Tea plant, an important beverage crop, is cultivated worldwide. Lignification can improve the hardness of tea plant, which is of great significance for tea quality. Jasmonates (JAs) and cytokinin are plant hormones that control processes of plant development and secondary metabolite accumulation. Hydroxycinnamoyl-CoA shikimate/quinate hydroxycinnamoyl transferase (HCT) is primarily involved in lignin biosynthesis. The effects of exogenous application of JAs and cytokinin on lignin biosynthesis and related HCT gene expression profiles in tea plants are still unclear. In order to investigate the effects of exogenous JAs and cytokinin on lignin accumulation, anatomical structures, and CsHCT gene profiles in tea plants, we treated tea plants with methyl jasmonate (MeJA) and cytokinin (6-BA). MeJA and 6-BA treatments triggered the lignification at 6 and 12d in tea leaves. The combined treatment resulted in an increase in lignin content at 6d, which was 1.32 times of that at 0d for 'Mengshan 9.' The CsHCTs in clade 2 (CsHCT5, CsHCT6, CsHCT7, and CsHCT8) were mainly expressed in leaves. We found that exogenous MeJA and cytokinin might be able to antagonistically regulate tea plant lignin accumulation through the mediation of CsHCT expression. This study revealed that HCTs play potential important roles involved in lignin biosynthesis of tea plant development and hormonal stimuli.

Cytokinin biosynthesis in cyanobacteria: Insights for crop improvement.

Cytokinins, a type of phytohormones that induce division of cytoplasm, have considerable value in agriculture due to their influences on several physiological processes of plants such as morphogenesis, development of chloroplast, seed dormancy, leaf senescence, etc. Previously, it was assumed that plants obtain cytokinin from the soil produced by microbes as these hormones were first discovered in soil-inhabiting bacteria i.e., Agrobacterium tumefaciens. Later, the cytokinin biosynthesis gene, i.e., ipt gene, has been reported in plants too. Though plants synthesize cytokinins, several studies have reported that the exogenous application of cytokinins has numerous beneficial effects including the acceleration of plant growth and boosting economic yield. Cyanobacteria may be employed in the soil not only as the source of cytokinins but also as the source of other plant growth-promoting metabolites. These organisms biosynthesize the cytokinins using the enzyme isopentenyl transferases (IPTs) in a fashion similar to the plants; however, there are few differences in the biosynthesis mechanism of cytokinins in cyanobacteria and plants. Cytokinins are important for the establishment of interaction between plants and cyanobacteria as evidenced by gene knockout experiments. These hormones are also helpful in alleviating the adverse effects of abiotic stresses on plant development. Cyanobacterial supplements in the field result in the induction of adventitious roots and shoots on petiolar as well as internodal segments. The leaf, root, and stem explants of certain plants exhibited successful regeneration when treated with cyanobacterial extract/cell suspension. These successful regeneration practices mark the way of cyanobacterial deployment in the field as a great move toward the goal of sustainable agriculture.

MdIPT8, an isopentenyl transferase enzyme, enhances the resistance of apple to Colletotrichum gloeosporioides infection

• Cytokinin enhances resistance to anthracnose in apple. • MdIPT8 responses C. gloeosporioides infection. • Overexpression of MdIPT8 increases apple resistance to C. gloeosporioides infection. Apple ( Malus domestica ) is a delicious fruit of high economic value. However, numerous destructive fungi affect apples, greatly limiting their production. Many studies have shown that salicylic acid and jasmonic acid improve plant resistance to fungal diseases, but the potential mechanisms of cytokinin action and fungal diseases remain largely unreported. The IPT gene family encodes the proteins required for cytokinin biosynthesis and plays a central role in plant biological progresses. In our previous study, we found that the disease resistance in autotetraploid apple was much better than ‘Hanfu’ diploid and analyzed the transcriptome data between ‘Hanfu’ diploid and autotetraploid apple. We found that the MdIPT8 gene was significantly differentially expressed. Therefore, we focused on gene family functions in cytokinin biosynthesis and biotic stress responses. We identified ten IPT genes in the ‘Hanfu’ whole genome that are unevenly distributed across the five apple chromosomes. Phylogenetic analysis indicated that this gene family belonged to two groups. Transcriptional analysis of the ten IPT genes indicated that MdIPT8 could be induced under Colletotrichum gloeosporioides infection in apple leaves. The MdIPT8 protein, when fused to the green fluorescent protein, identified the chloroplast as the site of protein localization. Finally, we confirmed that overexpression of MdIPT8 increased the resistance of C. gloeosporioides infection. Taken together, we have identified that the endogenous cytokinin content of ‘Hanfu’ leaves increased during C. gloeosporioides infection and the application of exogenous cytokinin improved the resistance of apple leaves to C. gloeosporioides and found that MdIPT8 can increase apple anthracnose resistance by improving the biosynthesis of cytokinin.

Genome-wide identification and expression analysis of the TaRRA gene family in wheat (Triticum aestivum L.).

Cytokinin is an important endogenous hormone in plants performing a wide spectrum of biological roles. The type-A response regulators (RRAs) are primary cytokinin response genes, which are important components of the cytokinin signaling pathway and are involved in the regulation of plant growth and development. By analysis of the whole genome sequence of wheat, we identified 20 genes encoding RRAs which were clustered into eight homologous groups. The gene structure, conserved motifs, chromosomal location, and cis-acting regulatory elements of the TaRRAs were analyzed. Quantitative real-time polymerase chain reaction (qRT-PCR) results showed that the expression levels of most of the TaRRAs increased rapidly on exogenous cytokinin application. Moreover, the TaRRA family members displayed different expression profiles under the stress treatments of drought, salt, cold, and heat. This study provides valuable insights into the RRA gene family in wheat and promotes the potential application of these genes in wheat genetic improvement.

OsDOF11 Promotes Crown Root Formation via Cytokinin in Oryza Sativa.

Crown root is the main part of root system, which performs an important role in rice growth and development, especially in nutrition and water assimilation. Previously, we reported negative feedback regulation loop between Oryza sativa DNA BINDING WITH ONE FINGER 11 (OsDOF11) and cytokinin by Oryza sativa CYTOKININ OXIDASE/DEHYDROGENASE 4 (OsCKX4) in rice development. Reverse transcription quantitative RT-PCR analyses was used to analyze the related gene transcript level. Nitrogen and hormone were measured by CHN-Nitrogen analyser and Liquid chromatography mass spectrometer, respectively. Exogenous application of cytokinin and [13C] sucrose labeled stable isotope uptake experiments help us to explain the relationship between OsDOF11 and cytokinin. We demonstrate the role of OsDOF11 in root development. We note that the loss function of OsDOF11 displays the reduced crown roots number, low activity of nitrogen assimilation and low content of cytokinin and auxin. The expression level of WUSCHEL-related homeobox (OsWOX11), A-type response regulator 2 (OsRR2), OsRR3, and OsCKX4 were decreased in osdof11-1, as well as in OsDOF11 RNA interference 9 mutants (RNAi-9 lines). Through Exogenous application of multiple concentrations of cytokinin as treatment to osdof11-1 mutant, RNAi-9 lines, and wild type (WT). We found that the crown roots number of osdof11-1 plants were rescued as the cytokinin concentration increased gradually from 1 μM to 10 μM, but the effect was weaker in RNAi-9 line. And cytokinin inhibited sucrose uptake activity from Murashige-Skoog medium with 3.0% sucrose (MS30) by OsDOF11 in rice root. OsDOF11 promotes crown root formation via cytokinin in oryza sativa. These results provide a physiological basis for further analysis of the OsDOF11 function of in rice root development.