Synthetic cytokinins control persimmon fruit shape, size and quality

Study on exogenous application of thidiazuron on seed size of Brassica napus L

Thidiazuron (TDZ) is a novel and efficient cytokinin commonly used in tissue culture, and numerous studies have demonstrated that TDZ can increase berry size. However, no study to date has explored the effect of TDZ on seed size of Brassica napus and the mechanism. To shed light on the effect of TDZ on the seed size of B. napus, four different concentrations of TDZ were applied to B. napus. Results indicated that TDZ treatment could increase the seed diameter and silique length of B. napus to varying degrees and 100 and 200 μmol/L TDZ treatments were the most effective with a 3.6 and 4.6% increase in seed diameter, respectively. In addition, the yield of B. napus was also substantially increased under TDZ treatment. On the other hand, confocal micrographs of embryos and cotyledon cells suggested that embryos and their cotyledon epidermal cells treated with 200 μmol/L TDZ were obviously larger in size than the control. Furthermore, TDZ promoted the upregulation of some key maternal tissue growth-related genes, including two G-protein signaling genes (AGG3 and RGA1) and two transcriptional regulators (ANT and GS2). The expression analysis of genes related to the auxin metabolic pathways, G-protein signaling, endosperm growth and transcriptional regulators confirmed that treatment with TDZ negatively regulated the key genes ABI5, AGB1, AP2, ARF2, and ARF18 during bud development stage and florescence. The results strongly suggested that TDZ might regulate the transcriptional levels of key genes involved in auxin metabolic pathways, G-protein signaling, endosperm growth and transcriptional regulators, which resulted in bigger cotyledon epidermal cells and seed size in B. napus. This study explored the mechanism of TDZ treatment on the seed size of B. napus and provided an important reference for improving rapeseed yield.

Applications of Cytokinins in Horticultural Fruit Crops: Trends and Future Prospects

Cytokinins (CKs) are a chemically diverse class of plant growth regulators, exhibiting wide-ranging actions on plant growth and development, hence their exploitation in agriculture for crop improvement and management. Their coordinated regulatory effects and cross-talk interactions with other phytohormones and signaling networks are highly sophisticated, eliciting and controlling varied biological processes at the cellular to organismal levels. In this review, we briefly introduce the mode of action and general molecular biological effects of naturally occurring CKs before highlighting the great variability in the response of fruit crops to CK-based innovations. We present a comprehensive compilation of research linked to the application of CKs in non-model crop species in different phases of fruit production and management. By doing so, it is clear that the effects of CKs on fruit set, development, maturation, and ripening are not necessarily generic, even for cultivars within the same species, illustrating the magnitude of yet unknown intricate biochemical and genetic mechanisms regulating these processes in different fruit crops. Current approaches using genomic-to-metabolomic analysis are providing new insights into the in planta mechanisms of CKs, pinpointing the underlying CK-derived actions that may serve as potential targets for improving crop-specific traits and the development of new solutions for the preharvest and postharvest management of fruit crops. Where information is available, CK molecular biology is discussed in the context of its present and future implications in the applications of CKs to fruits of horticultural significance.

Evolution of Lineage-Specific Gene Networks Underlying the Considerable Fruit Shape Diversity in Persimmon

The shapes of plant organs reflect the evolution of each lineage and have been diversified according to lineage-specific adaptations to environment. Research on the molecular pathways responsible for organ shapes has traditionally been focused mainly on leaves or flowers. Thus, little is known about the pathways controlling fruit shapes, despite their diversity in some plant species. In this study, we analyzed oriental persimmon (Diospyros kaki), which exhibits considerable diversity in fruit shapes among cultivars, to elucidate the underlying molecular mechanism using transcriptomic data and quantitative evaluation. First, to filter the candidate genes associated with persimmon fruit shapes, the whole gene expression patterns obtained using mRNA-Seq analysis from 100 individuals, including a segregated population and various cultivars, were assessed to detect correlations with principal component scores for fruit shapes characterized with elliptic Fourier descriptors. Next, a gene co-expression network analysis with weighted gene co-expression network analysis (WGCNA) package revealed that class 1 KNOX family genes and SEEDSTICK function as integrators along with some phytohormone-related genes, to regulate the fruit shape diversity. On the other hand, the OVATE family genes also contribute to fruit shape diversity, of which pathway would be potentially shared with other plant species. Evolutionary aspects suggest that acquisition of a high lineage-specific and variable expression of class 1 KNOX gene, knotted-like homeobox of Arabidopsis thaliana 1 (KNAT1), in young fruit is important for establishing the persimmon-specific mechanism that determines fruit shape diversity.

Changes in transcription of cytokinin metabolism and signalling genes in grape (Vitis vinifera L.) berries are associated with the ripening-related increase in isopentenyladenine

BACKGROUND

Cytokinins are known to play an important role in fruit set and early fruit growth, but their involvement in later stages of fruit development is less well understood. Recent reports of greatly increased cytokinin concentrations in the flesh of ripening kiwifruit (Actinidia deliciosa (A. Chev.) C.F. Liang & A.R. Ferguson) and grapes (Vitis vinifera L.) have suggested that these hormones are implicated in the control of ripening-related processes.

RESULTS

A similar pattern of isopentenyladenine (iP) accumulation was observed in the ripening fruit of several grapevine cultivars, strawberry (Fragaria ananassa Duch.) and tomato (Solanum lycopersicum Mill.), suggesting a common, ripening-related role for this cytokinin. Significant differences in maximal iP concentrations between grapevine cultivars and between fruit species might reflect varying degrees of relevance or functional adaptations of this hormone in the ripening process. Grapevine orthologues of five Arabidopsis (Arabidopsis thaliana L.) gene families involved in cytokinin metabolism and signalling were identified and analysed for their expression in developing grape berries and a range of other grapevine tissues. Members of each gene family were characterised by distinct expression profiles during berry development and in different grapevine organs, suggesting a complex regulation of cellular cytokinin activities throughout the plant. The post-veraison-specific expression of a set of biosynthesis, activation, perception and signalling genes together with a lack of expression of degradation-related genes during the ripening phase were indicative of a local control of berry iP concentrations leading to the observed accumulation of iP in ripening grapes.

CONCLUSIONS

The transcriptional analysis of grapevine genes involved in cytokinin production, degradation and response has provided a possible explanation for the ripening-associated accumulation of iP in grapes and other fruit. The pre- and post-veraison-specific expression of different members from each of five gene families suggests a highly complex and finely-tuned regulation of cytokinin concentrations and response to different cytokinin species at particular stages of fruit development. The same complexity and specialisation is also reflected in the distinct expression profiles of cytokinin-related genes in other grapevine organs.