Motility-Independent Vertical Transmission of Bacteria in Leaf Symbiosis

Structures and roles of BcsD and partner scaffold proteins in proteobacterial cellulose secretion

Cellulose is the world's most abundant biopolymer, and similar to its role as a cell wall component in plants, it is a prevalent constituent of the extracellular matrix in bacterial biofilms. Although bacterial cellulose (BC) was first described in the 19th century, it was only recently revealed that it is produced by several distinct types of Bcs secretion systems that feature multiple accessory subunits in addition to a catalytic BcsAB synthase tandem. We recently showed that crystalline cellulose secretion in the Gluconacetobacter genus (α-Proteobacteria) is driven by a supramolecular BcsH-BcsD scaffold-the "cortical belt"-which stabilizes the synthase nanoarrays through an unexpected inside-out mechanism for secretion system assembly. Interestingly, while bcsH is specific for Gluconacetobacter, bcsD homologs are widespread in Proteobacteria. Here, we examine BcsD homologs and their gene neighborhoods from several plant-colonizing β- and γ-Proteobacteria proposed to secrete a variety of non-crystalline and/or chemically modified cellulosic polymers. We provide structural and mechanistic evidence that through different quaternary structure assemblies BcsD acts with proline-rich BcsH, BcsP, or BcsO partners across the proteobacterial clade to form synthase-interacting intracellular scaffolds that, in turn, determine the biofilm strength and architecture in species with strikingly different physiology and secreted biopolymers.

Seed-to-Seed: Plant Core Vertically Transmitted Microbiota

The plant core microbiota transmitted by seeds have been demonstrated to exist in seeds and adult plants of several crops for multiple generations. They are closely related to plants and are relatively conserved throughout evolution, domestication, and breeding. These microbiota play a vital role in the early stages of plant growth. However, information about their colonization routes, transmission pathways, and final fate remains fragmentary. This review delves into the concept of these microbiota, their colonization sources, transmission pathways, and how they change throughout plant evolution, domestication, and breeding, as well as their effects on plants, based on relevant literature. Finally, the significant potential of incorporating the practical application of seed-transmitted microbiota into plant microbial breeding is emphasized.