Function of Cyclophilin1 as a long-distance signal molecule in the phloem of tomato plants

Systemic Signaling: A Role in Propelling Crop Yield

Food security has become a topic of great concern in many countries. Global food security depends heavily on agriculture that has access to proper resources and best practices to generate higher crop yields. Crops, as with other plants, have a variety of strategies to adapt their growth to external environments and internal needs. In plants, the distal organs are interconnected through the vascular system and intricate hierarchical signaling networks, to communicate and enhance survival within fluctuating environments. Photosynthesis and carbon allocation are fundamental to crop production and agricultural outputs. Despite tremendous progress achieved by analyzing local responses to environmental cues, and bioengineering of critical enzymatic processes, little is known about the regulatory mechanisms underlying carbon assimilation, allocation, and utilization. This review provides insights into vascular-based systemic regulation of photosynthesis and resource allocation, thereby opening the way for the engineering of source and sink activities to optimize the yield performance of major crops.

Reinvigoration/Rejuvenation Induced through Micrografting of Tree Species: Signaling through Graft Union

Trees have a distinctive and generally long juvenile period during which vegetative growth rate is rapid and floral organs do not differentiate. Among trees, the juvenile period can range from 1 year to 15–20 years, although with some forest tree species, it can be longer. Vegetative propagation of trees is usually much easier during the juvenile phase than with mature phase materials. Therefore, reversal of maturity is often necessary in order to obtain materials in which rooting ability has been restored. Micrografting has been developed for trees to address reinvigoration/rejuvenation of elite selections to facilitate vegetative propagation. Generally, shoots obtained after serial grafting have increased rooting competence and develop juvenile traits; in some cases, graft-derived shoots show enhanced in vitro proliferation. Recent advances in graft signaling have shown that several factors, e.g., plant hormones, proteins, and different types of RNA, could be responsible for changes in the scion. The focus of this review includes (1) a discussion of the differences between the juvenile and mature growth phases in trees, (2) successful restoration of juvenile traits through micrografting, and (3) the nature of the different signals passing through the graft union.

Enzyme activity and structural features of three single-domain phloem cyclophilins from Brassica napus

Cyclophilins (CYPs) are a group of ubiquitous prolyl cis/trans isomerases (PPIases). It was shown that plants possess the most diverse CYP families and that these are abundant in the phloem long-distance translocation stream. Since phloem exudate showed PPIase activity, three single-domain CYPs that occur in phloem samples from Brassica napus were characterised on functional and structural levels. It could be shown that they exhibit isomerase activity and that this activity is controlled by a redox regulation mechanism, which has been postulated for divergent CYPs. The structure determination by small-angle X-ray scattering experiments revealed a conserved globular shape. In addition, the high-resolution crystal structure of BnCYP19-1 was resolved and refined to 2.0 Å resolution, and the active sites of related CYPs as well as substrate binding were modelled. The obtained data and results support the hypothesis that single domain phloem CYPs are active phloem PPIases that may function as chaperones.

Down-regulation of SlCyp1 in the phloem reduces auxin response and photosynthetic rate in tomato (Solanum lycopersicum) plants

The tomato dgt mutant, containing a single mutation in the Cyclophilin1 (SlCyp1) gene, is auxin insensitive and exhibits a pleotropic phenotype that includes lack of lateral roots, malformed xylem structure and reduced root-to-shoot ratio. Recently, we found that the SlCyp1 protein is phloem-mobile and traffic from shoot to root to induce lateral root formation. These processes are achieved through activation of auxin-mediated developmental programs. Inhibition of the trafficked SlCyp1 activity at the target site resulted in inhibition of the auxin response, supporting the hypothesis that this protein is indeed a mobile signal. Here, we show that partial silencing of SlCyp1 in the phloem only resulted in perturbed auxin response in the roots and reduced photosynthetic and transpiration rates. The presented data suggests that expression of SlCyp1 in the phloem is essential for proper auxin response at the whole plant level. We, therefore, propose that this protein acts as a long-distance signaling molecule acting as coordinator between roots and shoot activities.