Stefan de Folter

SUMMARY: The transcription factor WIP2/NO TRANSMITTING TRACT (WIP2/NTT) belongs to the WIP zinc finger family. Loss of WIP/NTT function in Arabidopsis thaliana causes alterations in specific tissues in the gynoecium. It also impairs root development, but only when combined with the loss of WIP4 and WIP5 function, due to redundancy. Certain mutant loss‐of‐function phenotypes can be recovered by cytokinin application, NTT interacts with cytokinin signaling components, and the phenotypes displayed by plants with increased WIP2/NTT expression also suggest a possible interaction with this pathway. Therefore, the objective of this study was to investigate the relationship between WIP2/NTT and the cytokinin pathway. To overcome the issue of genetic redundancy, we used a commonly used inducible system. We found that WIP2/NTT induction alters cytokinin levels and signaling in a tissue‐specific manner, as shown by cytokinin content measurements and TCSn::GFP reporter analysis. Transcriptome analyses revealed candidate target genes related to the cytokinin pathway. Yeast one‐hybrid and transactivation assays demonstrated direct NTT binding to regulatory regions of the cytokinin genes ISOPENTENYL TRANSFERASE 5 (IPT5) , ARABIDOPSIS HISTIDINE PHOSPHOTRANSFER PROTEIN 6 (AHP6) , and CYTOKININ OXIDASE/DEHYDROGENASE 7 (CKX7) involved in cytokinin biosynthesis, signaling, and degradation, respectively. Moreover, immunolocalization assays revealed that cytokinin distribution was altered in loss of function mutants and after NTT induction. The results of this work indicate that WIP2/NTT modulates cytokinin homeostasis.

Plant organ initiation requires precise spatial and temporal coordination of cellular behaviors. In Arabidopsis, the gynoecium, the female reproductive structure formed by two fused carpels, is initiated after the termination of the floral meristem. Proper initiation of the carpels is crucial for ovule protection, successful fertilization, and the formation of diverse fruit structures. While the phytohormones auxin and cytokinin are known to regulate organogenesis, their interplay during the earliest stages of carpel development is not fully understood. In particular, how auxin–cytokinin crosstalk influences growth patterns that shape the emerging gynoecium remains unknown. Here, we combined confocal live imaging, hormone treatments, and hormone reporters to capture at cellular resolution the dynamic processes of cell expansion and division that drive the onset of the carpel developmental program. We show that carpel primordia initiation is driven by growth differences between the fast-expanding peripheral and slow-growing central regions, transforming the dome-shaped floral meristem into two fused carpels connected by a continuous ring of cells. Ectopic cytokinin treatments increase cell growth and division to promote an increase in the size of the carpel primordia, whereas inhibition of auxin transport has the opposite effect. Our results suggest that the interplay between auxin and cytokinin is indispensable for establishing the correct organ geometry during carpel initiation.

The formation of plant organs requires a cascade of regulatory processes which triggers gene expression, protein synthesis, and biochemical reactions that shape cellular structures and functions. Central to these processes are proteins, often transcription factors, which rarely work alone, but in cooperation with other proteins to form dynamic interactions to achieve correct regulation. In this review, we explore the role of protein–protein interactions in flower and fruit development. For this, we start with transcription factors and how their functions are modulated through physical interactions with other proteins. We list a set of current techniques to study protein interactions in reproductive development, along with emerging methodologies. Additionally, we discuss key molecular mechanisms mediated by protein–protein interactions such as recognition specificity, DNA binding, and protein complex formation. Finally, we describe some current challenges and future directions in the study of flower development.

Main conclusion: We identified new players of male and female reproductive development using tissue-specific gynoecium transcriptome data of Arabidopsis. Reproductive success in angiosperms depends on the correct development of the male and female organs. Pollen grains will land and germinate on the stigma, followed by the growth of pollen tubes that pass through the transmitting tract system of the gynoecium to reach the ovules. After the fertilization process occurred, seed and fruit development initiates. Genetic networks direct these biological processes needed for flower and fruit development to occur. Although many genes have been identified, still genes are to be discovered also to be involved in these networks. The availability of transcriptomic data from specific tissues of the gynoecium in Arabidopsis allowed us to select genes for functional analysis. As a result, from the analysis of the mutant plants we found that the genes CLE19, TBL36, ATHB5, CYCP4;1, AT3G06035, and AT1G15760 affect fertility in Arabidopsis. The mutant plants showed gynoecia with aborted ovules and short fruits with a lower number of seeds compared to wild type. Furthermore, pollen development and pollen tube growth were affected in most of the mutants. These results help us know and understand the genes that contribute to flower development in Arabidopsis.

This article comments on: Álvarez-Urdiola R, Matus JT, González-Miguel VM, Bernardo-Faura M, Riechmann JL. 2025. Chronology of transcriptome and proteome expression during early Arabidopsis flower development. Journal of Experimental Botany 76, 2743–2762 https://doi.org/10.1093/jxb/eraf005

SUMMARY: In angiosperms, the gynoecium is the female reproductive structure, whose function is to contain the ovules and promote their fertilization. In Arabidopsis, the gynoecium develops from a small primordium with meristematic properties to a complex structure with internal and external specialized tissues. Due to its anatomical and developmental complexity, it is challenging to study in vivo the developmental processes of the gynoecium. Although efforts have been made, there are still unanswered questions, especially those related to cell proliferation of internal tissues. Here, we use confocal imaging to study the cell cycle, the proliferation of internal tissues, and the relationship with cytokinin signaling. We observed that early gynoecium proliferation is complex and with a long cell cycle dynamics. Moreover, we observed a relationship between the region of highest proliferation and maximum cytokinin signaling, a rise in proliferation attributed to BAP treatment, ectopic tissue formation with cytokinin signaling, and alterations in the gynoecium primordium in mutant lines. Together, these results provide insights into cell cycle dynamics, meristematic maintenance, and medial tissue development in the Arabidopsis gynoecium.

BOL/DRNL/ESR2, an AP2/ERF transcription factor, regulates early organ development in Arabidopsis (Arabidopsis thaliana). Its loss of function causes flower organ defects, while its overexpression induces green callus formation in roots without the addition of hormones. Jasmonates, plant hormones known as major players in stress responses, also regulate some aspects of organ development (e.g., stamen development and plant and organ growth). Here, we studied the interaction between BOL and the JA pathway. We found that exogenous application of methyl jasmonate (MeJA) partially rescued the stamen phenotypes in bol-cr mutants, linking BOL and JA-mediated stamen development. Moreover, MeJA treatments in wild-type plants partially mimicked some bol-D mutant phenotypes like reduced rosette and root size, while JA inhibition restored wild-type leaf curvature, suggesting an alteration in JA homeostasis in the gain-of-function mutant. BOL overexpression caused increased JA levels, whereas bol loss-of-function plants had reduced levels. Furthermore, inducible BOL activity led to downregulation of a JA-responsive marker. Finally, JA biosynthesis inhibition affected BOL-induced root callus formation and led to an expansion of the BOL expression domain in roots. Our findings indicate that BOL modulates parts of the JA pathway and that feedback from the JA pathway appears to affect expression of the transcription factor.