Cross-talk between Copper Homeostasis and Plant Development
Overview
As a result of their potent chemical properties, metals, such as copper, zinc and iron have been selected during evolution for roles as essential cofactors of numerous proteins indispensable for all biological life. Plants are faced with the challenge that in most soils, bioavailable concentrations of these essential nutrients are generally very low, and often limiting. Hence it is conceivable, and supported by some scattered experimental evidence, that metal nutrient status might exert a regulatory influence also on developmental processes in plants. However, targeted studies addressing this and the underlying regulatory mechanisms are scarce, and metal availability has rarely been adjusted to levels common in natural environments, or even controlled, in research on plant development.
Figure 1: Plant copper status affects development. Shown are Arabidopsis thaliana grown in hydroponic culture under Cu deficiency (left, no added Cu), Cu sufficient conditions (middle, 0.5 µM Cu), and Cu toxicity (right, 1.5 µM Cu).
Plant copper (Cu) nutritional status strongly affects flower fertility and flowering time, but the molecular basis for this is not understood. Whereas several Arabidopsis thaliana Squamosa Promoter binding protein-Like (SPL) family transcription factors have been implicated in plant developmental processes, Arabidopsis thaliana spl7 mutants are defective in a transcription factor that controls a large set of central Cu deficiency responses. These mutants are also physiologically more Cu-deficient than the wild type. Moreover, the response of flowering time to Cu deficiency is strongly aberrant in spl7 mutants. Here we propose to elucidate at the molecular level the cross-talk between Cu homeostasis and flowering time control, as well as the regulatory relationships between the Cu homeostasis network and responses to endogenous sugars. We will employ micronutrient-controlled growth conditions for an in-depth analysis of the influence of plant Cu status and loss of SPL7 function on flowering time.
Subsequently, a reverse genetic approach will be pursued to dissect the interactions between Cu nutritional status, the Cu homeostasis network and the regulatory network of flowering time control. We will address the functions of the subgroup of SPL transcription factors which is less well characterized to date and not targeted by microRNA156, in Cu homeostasis and metal-dependent modulation of plant development.
This work will reveal how regulatory processes can be triggered dependent on plant nutrient status of Cu, an essential transition metal distinctive by the strongest binding to ligand molecules out of all nutrient metal cations. An improved understanding of the interaction between the copper homeostasis network and flowering time control will expand our knowledge of the metabolic control of plant development. Finally, this work will be instrumental for increasing crop yields and yield quality on soils deficient in bioavailable Cu, which comprise approximately one fifth of the cultivated area.
