Plant hormones (Literature sources on phytohormones and plant signalling)

Authors: Yuyuan Ma, Yu Wang, Zhiqin Zhou, Runqin Zhang, Yiru Xie, Yihan Zhang, Yongming Bo, Xiaolong Lyu, Jinghua Yang, Mingfang Zhang and Zhongyuan Hu.

Theoretical and Applied Genetics (2024)

Key message: The ClLOG gene encoding a cytokinin riboside 5ʹ-monophosphate phosphoribohydrolase determines trichome length in watermelon, which is associated with its promoter variations.

Abstract: "Trichomes, which are differentiated from epidermal cells, are special accessory structures that cover the above-ground organs of plants and possibly contribute to biotic and abiotic stress resistance. Here, a bulked segregant analysis (BSA) of an F2 population with significant variations in trichome length was undertaken. A 1.84-Mb candidate region on chromosome 10 was associated with trichome length. Resequencing and fine-mapping analyses indicated that a 12-kb structural variation in the promoter of Cla97C10G203450 (ClLOG) led to a significant expression difference in this gene in watermelon lines with different trichome lengths. In addition, a virus-induced gene silencing analysis confirmed that ClLOG positively regulated trichome elongation. These findings provide new information and identify a potential target gene for controlling multicellular trichome elongation in watermelon."

Authors: Weikun Jing, Guoqin Liu, Feifei Gong, Yinglong Deng, Jiaqi Liu, Wenjing Yang, Xiaoming Sun, Yonghong Li, Junping Gao, Xiaofeng Zhou and Nan Ma.

Research Square (2022)

Abstract: "The size of lateral organs is determined by well-coordinated cell proliferation and cell expansion. The transition from cell proliferation to expansion remains a largely unknown question in plant biology. Here, we report that miR159, an evolutionarily conserved microRNA, plays a crucial role in the transition from cell proliferation to expansion in rose (Rosa hybrida) petals through governing rapid cytokinin catabolism. We uncovered that Cytokinin Oxidase/Dehydrogenase 6 (CKX6) is an authentic target of miR159 in petals. Knocking down miR159 levels resulted in the accumulation of CKX6 transcripts and precocious cytokinin clearance, consequently leading to an earlier transition to cell expansion and smaller petals. Conversely, knockdown of CKX6 caused excess cytokinin and delayed cell expansion, mimicking the effects of exogenous cytokinin application. MYB73, a R2R3-type MYB transcription repressor, recruited a co-repressor (TOPLESS) and a histone deacetylase (HDA19) to form a suppression complex, which governed the expression of MIR159 by modulating H3K9 acetylation levels at the MIR159 promoter. This work thus provides insights for ensuring correct timing of cell expansion and organ size via control of cytokinin catabolism."

Authors: Sumeera Asghar, Nida Ghori, Faisal Hyat, Yan Li and Chunli Chen

Plant Growth Regulation (2023)

Abstract: "Plant growth regulators (PGRs) enhance plants regeneration ability to form various organs and tissues by determining embryonic fate in vivo and boosting regeneration efficiency in vitro. Recent advances in molecular biology have identified that auxin and cytokinin biosynthesis, transportation, and signaling affect cell fate both transcriptionally and non-transcriptionally. Growth regulators have a key role in cell reprogramming. The ratio between auxin and cytokinin application in the plant tissue culture can control the state of cell di- or dedifferentiation. In this study, the different regenerative pathways of these PGRs are systematically overviewed for the first time, with the objective of better understanding somatic embryogenesis. Secondly, the different biosynthetic and signaling pathways of auxin and cytokinin interactions are thoroughly discussed. Finally, future research directions are identified for somatic embryogenesis. This review article provides a unique reference for a wide range of plant science communities to narrate the recent developments of auxin and cytokinin-related signaling and developmental pathways for a better understanding of the regeneration phenomena of somatic embryogenesis."

Authors: Lijun Gan, Mengying Song, Xuechun Wang, Na Yang, Hu Li, Xuexia Liu and Yi Li.

Horticulture Research (2022)

Abstract: "Although cytokinins (CKs) regulate fruit development, no direct genetic evidence supports the role of endogenous CKs in pericarp growth or development or fruit size. Here, we report that the reduction in endogenous active CKs level via overexpression of a CKs-inactivating enzyme gene AtCKX2 specifically in fruit tissues resulted in reduced pericarp thickness and smaller fruit size, compared to wild-type control fruits. The pericarp thickness and single fruit weight in transgenic plants were significantly reduced. Analysis of paraffin sections showed that the reduced pericarp thickness was due largely to a decreased number of cells, and thus decreased cell division. Transcriptome profiling showed that the expression of cell division– and expansion–related genes was reduced in AtCKX2-overexpressing fruits. In addition, the expression of auxin-signaling and gibberellin-biosynthetic genes was repressed, whereas that of gibberellin-inactivating genes was enhanced, in AtCKX2-overexpressing fruits. These results demonstrate that endogenous CKs regulate pericarp cell division and, subsequently, fruit size. They also suggest that CKs interact with auxin and gibberellins in regulating tomato pericarp thickness and fruit size."