A Constitutively Active Cytokinin Receptor Variant Increases Cambial Activity and Stem Growth in Poplar

Deletion of the PtrDJ1C gene leads to increased branching in poplar

The PtrDJ1C gene is essential for poplar growth and early chloroplast development. Disruption of PtrDJ1C expression results in an albino leaf phenotype and increased branching. However, the underlying mechanism for the increased branching remains unknown. In this study, we employed integrated approaches to investigate the function of PtrDJ1C in the branch-increasing phenotype. Our results revealed that levels of indole-3-acetic acid (IAA), gibberellin (GA), and abscisic acid (ABA) were significantly reduced in ptrdj1c mutants, while cytokinin (CK) levels were slightly increased. Transcriptomic and proteomic analyses identified several key genes and proteins involved in hormone regulation and branching development that were differentially expressed. Specifically, the expression levels of TAA, ZEP, and GA20ox-genes involved in IAA, GA, and ABA biosynthesis-were significantly reduced in ptrdj1c, while IPT and LOG, which regulate CK synthesis, were upregulated. Moreover, immunoblot analysis further validated reduced levels of key biosynthetic enzymes for IAA, GA, and ABA, alongside increased levels of IPT and LOG enzymes. Interestingly, our findings suggest that hormone signaling pathways act in concert with the transcription factor WUSCHEL (WUS) to synergistically promote branching development. These results provide novel insight into the regulatory role of PtrDJ1C in hormone balance and its downstream effects on poplar branching.

Cytokinin and reproductive shoot architecture: bigger and better?

Cytokinin (CK) is a key plant hormone, but one whose effects are often misunderstood, partly due to reliance on older data from before the molecular genetic age of plant science. In this mini-review, we examine the role of CK in controlling the reproductive shoot architecture of flowering plants. We begin with a long overdue re-examination of the role of CK in shoot branching, and discuss the relatively paucity of genetic evidence that CK does play a major role in this process. We then examine the role of CK in determining the number of inflorescences, flowers, fruit and seed that plants initiate during reproductive development, and how these are arranged in space and time. The genetic evidence for a major role of CK in controlling these processes is much clearer, and CK has profound effects in boosting the size and number of most reproductive structures. Conversely, the attenuation of CK levels during the reproductive phase likely contributes to reduced organ size seen later in flowering, and the ultimate arrest of inflorescence meristems during end-of-flowering. We finish by discussing how this information can potentially be used to improve crop yields.

Wood of trees: Cellular structure, molecular formation, and genetic engineering

Wood is an invaluable asset to human society due to its renewable nature, making it suitable for both sustainable energy production and material manufacturing. Additionally, wood derived from forest trees plays a crucial role in sequestering a significant portion of the carbon dioxide fixed during photosynthesis by terrestrial plants. Nevertheless, with the expansion of the global population and ongoing industrialization, forest coverage has been substantially decreased, resulting in significant challenges for wood production and supply. Wood production practices have changed away from natural forests toward plantation forests. Thus, understanding the underlying genetic mechanisms of wood formation is the foundation for developing high-quality, fast-growing plantation trees. Breeding ideal forest trees for wood production using genetic technologies has attracted the interest of many. Tremendous studies have been carried out in recent years on the molecular, genetic, and cell-biological mechanisms of wood formation, and considerable progress and findings have been achieved. These studies and findings indicate enormous possibilities and prospects for tree improvement. This review will outline and assess the cellular and molecular mechanisms of wood formation, as well as studies on genetically improving forest trees, and address future development prospects.