Stromules

Introduction to Plastid Stromules

Stromules, which are slender tubular structures that extend from the surface of plastids, were first observed by Haberland in Selaginella kraussiana cells during the 19th century. Although Wildman and colleagues contributed to their documentation in the 1960s, stromules remained largely neglected until recently. These stroma-filled protrusions have gained significance for researchers as they offer potential insights into both communication between plant organelles and regulation of plastid function. The term „stromules“ was initially used to describe these structures and continues to be utilized today when discussing them academically. Electron microscopy has revealed that stromules are double-membrane structures consisting of both outer and inner envelopes of plastids. While more abundant in non-photosynthetic tissues, stromules have also been detected in plastids of various cell types and plant species.

Stromule Formation and Function

Despite their ubiquity, the precise function of stromules remains unknown. They are believed to perform conserved roles in plastid biology, and the morphology and frequency of stromules have been found to be tightly regulated with developmental stages, physiological conditions, and cellular contexts. Diverse functions have been proposed for stromules, including de novo extensions from the plastid surface, tubular connections that link recently divided or actively dividing plastids, and tubular extensions that shed globular, stroma-filled vesicles. Their differential distribution in both time and space, with high frequencies found in non‐green organs such as roots and cultured suspension cells, indicates that stromules may have specific roles in different cellular contexts that are yet to be fully understood. Recent studies have highlighted their potential importance of stromules in facilitating metabolic and signaling pathways within and between plastids, as well as their role in plant responses to environmental stresses.

Molecular Mechanisms Regulating Stromule 

Despite the growing interest in stromules, little is known about their molecular mechanisms of regulation. As scientists delve deeper into the fascinating world of stromules, they are uncovering a wealth of information regarding the complex signaling pathways and molecular mechanisms that govern their formation and regulation. Emerging research has identified numerous proteins potentially involved in these critical processes, providing new insight into how cells control stromule development at a molecular level. By elucidating these intricate cellular systems, researchers can gain a more comprehensive understanding of this enigmatic phenomenon’s functions across varying species and physiological contexts.

Current Research on Plastid Stromules in Our Lab

In my lab we are addressing the fundamental questions regarding the roles and regulation of plastid stromules by following three main approaches:

1. One way to expand our knowledge on stromule biology is by utilizing screening and transcriptomic techniques to identify genes that play a role in regulating stromules.
2. Another significant aspect of expanding academically about the function of stromules would be analyzing which molecular motors are responsible for the formation of these projections from plastids.
3. Studying how stromules contribute towards interactions between plastid nuclei along with signaling pathways can also provide valuable insights into their functions within different cellular contexts.

Future Directions in Stromule Studies

Given the limited understanding of plastid stromules, there are numerous opportunities for future research in this field. we are currently exploring the following two new directions:

1. Modeling stromules based on cell biological observations

The elusive function of stromules signifies an imperative requirement for interdisciplinary investigations in this domain. Mathematical modeling predicated on cell biological observations can potentially illuminate the ambiguous functions and significance of stromules within cellular contexts, particularly during stress-induced situations.

A preliminary investigation was carried out recently to investigate the impact of stromule formation on the infiltration of plastids into cortical cytoplasm in leaf epidermis cells. The outcomes indicated that stromules can augment the surface interaction between plastids and cytoplasm. Nonetheless, this effect is more pronounced when linked with the distribution of plastids within the cell, which was evident in this particular type. This demonstrates how these approaches can be advantageous for understanding organelle morphology and position.

2. Synthetic biology to gain insight into stromules

What is synthetic biology? Synthetic biology is a field of research that applies engineering principles to the design and construction of biological systems with defined functions. Synthetic biology approaches can also provide valuable insights into the roles and regulation of stromules. By constructing synthetic systems with varying stromule properties, we can investigate how these structures affect cellular biology and potentially manipulate their functions to gain insight into their biological role.

Concluding Remarks on the Significance of Plastid Stromules

In conclusion, understanding the roles and regulation of plastid stromules is critical to comprehending various biological processes in plant cells. Recent studies continue to shed light on the potential functions of these structures in transferring signals from plastids to nuclei and maintaining the resulting plastid-nuclear complex. However, significant gaps in our knowledge remain, particularly concerning how stromule formation is regulated at a molecular level and what specific signaling pathways are involved. Interdisciplinary collaborations across biology, mathematics, and physics can expand our knowledge in this area, leading to new discoveries with implications for plant biology as well as medicine and biotechnology.