GTL1 keeps cell growth and nuclear ploidy under control

A cotton endoreduplication gene, GaTOP6B, regulates trichome branching development

Trichomes are specialized epidermal structures that protect plants from biotic and abiotic stresses by synthesizing, storing, and secreting defensive compounds. This study investigates the role of the Gossypium arboreum DNA topoisomerase VI subunit B gene (GaTOP6B) in trichome development and branching. Sequence alignment revealed a high similarity between GaTOP6B and AtTOP6B, suggesting a conserved function in trichome regulation. Although AtTOP6B acts as a positive regulator of trichome development, functional analyses showed contrasting effects: Virus-induced gene silencing (VIGS) of GaTOP6B in cotton increased trichome density, while its overexpression in Arabidopsis decreased trichome density but enhanced branching. This demonstrates that GaTOP6B negatively regulates trichome number, indicating species-specific roles in trichome initiation and branching between cotton and Arabidopsis. Overexpression of the GaTOP6B promotes jasmonic acid synthesis, which in turn inhibits the G1/S or G2/M transitions, stalling the cell cycle. On the other hand, it suppresses brassinolide synthesis and signaling while promoting cytokinin degradation, further inhibiting mitosis. These hormonal interactions facilitate the transition of cells from the mitotic cycle to the endoreduplication cycle. As the level of endoreduplication increases, trichomes develop an increased number of branches. These findings highlight GaTOP6B's critical role as a regulator of trichome development, providing new genetic targets for improving cotton varieties in terms of enhanced adaptability and resilience.

Yellowhorn Xso-miR5149-XsGTL1 enhances water-use efficiency and drought tolerance by regulating leaf morphology and stomatal density

Yellowhorn (Xanthoceras sorbifolium) is a unique edible woody oil tree species in China. Drought stress is the major yield-limiting factor of yellowhorn. MicroRNAs play an important role in regulating the response of woody plants to drought stress. However, the regulatory function of miRNAs in yellowhorn remains unclear. Here, we first constructed coregulatory networks integrated with miRNAs and their target genes. According to GO function and expression pattern analysis, we selected the Xso-miR5149-XsGTL1 module for further study. Xso-miR5149 is a key regulator of leaf morphology and stomatal density by directly mediating the expression of the transcription factor XsGTL1. Downregulation of XsGTL1 in yellowhorn led to increased leaf area and reduced stomatal density. RNA-seq analysis indicated that downregulation of XsGTL1 increased the expression of genes involved in the negative control of stomatal density, leaf morphology, and drought tolerance. After drought stress treatments, the XsGTL1-RNAi yellowhorn plants were less damaged and had higher water-use efficiency than the WT plants, while destruction of Xso-miR5149 or overexpression of XsGTL1 had the opposite effect. Our findings indicated that the Xso-miR5149-XsGTL1 regulatory module plays a critical role in controlling leaf morphology and stomatal density; hence, it's a potential candidate module for engineering enhanced drought tolerance in yellowhorn.

Comparative transcriptome atlases reveal altered gene expression modules between two Cleomaceae C3 and C4 plant species

C(4) photosynthesis outperforms the ancestral C(3) state in a wide range of natural and agro-ecosystems by affording higher water-use and nitrogen-use efficiencies. It therefore represents a prime target for engineering novel, high-yielding crops by introducing the trait into C(3) backgrounds. However, the genetic architecture of C(4) photosynthesis remains largely unknown. To define the divergence in gene expression modules between C(3) and C(4) photosynthesis during leaf ontogeny, we generated comprehensive transcriptome atlases of two Cleomaceae species, Gynandropsis gynandra (C(4)) and Tarenaya hassleriana (C(3)), by RNA sequencing. Overall, the gene expression profiles appear remarkably similar between the C(3) and C(4) species. We found that known C(4) genes were recruited to photosynthesis from different expression domains in C(3), including typical housekeeping gene expression patterns in various tissues as well as individual heterotrophic tissues. Furthermore, we identified a structure-related module recruited from the C(3) root. Comparison of gene expression patterns with anatomy during leaf ontogeny provided insight into genetic features of Kranz anatomy. Altered expression of developmental factors and cell cycle genes is associated with a higher degree of endoreduplication in enlarged C(4) bundle sheath cells. A delay in mesophyll differentiation apparent both in the leaf anatomy and the transcriptome allows for extended vein formation in the C(4) leaf.