SXRF shows anthers have a craving for copper

Using micro-XRF imaging capability at F3 beamline, the research group led by Olena K. Vatamaniuk has linked the role of the micronutrient copper with pollen fertility and seed/grain yield.

The global demand for high-yield crops is increasing with growing population and decreasing farmland resources. These trends force the utilization of marginal lands for agricultural purposes. The bioavailability of essential mineral nutrients such as copper in these soils is often low, causing the reduced crop growth and fertility, and consequently low grain yield or even total crop failure. Although copper is recognized as an essential micronutrient for plant fertility, scientists still do not completely know which reproductive structures of plants require copper, how copper is delivered there and how copper transport processes are regulated. These questions are currently being addressed in the Vatamaniuk lab using model plants Arabidopsis thaliana and Brachypodium distachyon as well as a crop species, wheat, Triticum aestivum.

In studies using A. thaliana, the Vatamaniuk research group identified a new protein, CITF1, whose transcript accumulates in A. thaliana flowers during periods of copper deficiency. CITF1 acts as a transcription regulator: it regulates copper uptake into the roots and its delivery to flowers, working in tandem with SPL7 that is the central regulator of copper homeostasis in this plant species. When SPL7 and CITF1 do not function, as in the citf1 spl7 double mutant, its seedlings die and its pollen becomes infertile. Working with CHESS scientist, Rong Huang, at F3 beamline, a member of the Vatamaniuk research group, Ju-Chen Chia has shown that the sites of pollen production, anthers of flowers, accumulate the majority of the absorbed copper in A. thaliana. Huang and Chia also showed that copper accumulation was somewhat lower in anthers and carpels of the citf1 mutant and was further reduced in anthers and carpels of the spl7 mutant compared to wild-type plants (Fig. 1). They also showed that the majority of anthers of the citf1 spl7 double mutant lacked copper and that this deficiency resulted in pollen infertility.

This XRF work at CHESS contributed to the discovery that successful pollen fertility in Arabidopsis thaliana requires copper delivery to anthers and the essential role of CITF1 and SPL7 in the regulation of copper transport processes. These new findings will provide scientists with new ideas for their efforts to develop crops, which are better suited to grow in soils considered marginal and with higher yields on soils currently in cultivation. The next step of Vatamaniuk lab is to use 3D XRF-based confocal microscopy and computed tomography to understand the spatial distribution of  copper in specific anther structures and pollens down to the cellular level in A. thaliana. The Vatamaniuk lab will also use micro-XRF to study the role of copper and the SPL7- and CITF1-like proteins in copper delivery to the reproductive organs and fertility in wheat, and the wheat proxy, B. distachyon.

This project in the Vatamaniuk lab has been supported by the National Science Foundation through Grant IOS 1656321.

To read the full research article, please see:

SXRF analysis Cu Fe
viability analysis pollen grains
Figure 1 A-C shows SXRF analysis of Cu (A) and Fe (B) localization in the wild type and indicated mutant lines compared to total fluorescence density (C). Note that only Cu but not Fe accumulation has changed in each of the mutant lines and that Cu was barely detectable in the double mutant. D shows viability analysis of pollen grains in anthers of indicated lines. Viable pollen grains were stained dark and light violet, while non-viable pollen grains were pale turquoise. Note that the citf1 spl7 double mutant accumulates significantly less Cu in anthers (A, white arrows), and has significantly less viable pollen.