Metallothionein deficiency impacts copper accumulation and redistribution in leaves and seeds of Arabidopsis.

Most angiosperm genomes contain several genes encoding metallothionein (MT) proteins that can bind metals including copper (Cu) and zinc (Zn). Metallothionein genes are highly expressed under various conditions but there is limited information about their function. We have studied Arabidopsis mutants that are deficient in multiple MTs to learn about the functions of MTs in plants. T-DNA insertions were identified in four of the five Arabidopsis MT genes expressed in vegetative tissues. These were crossed to produce plants deficient in four MTs (mt1a/mt2a/mt2b/mt3). The concentration of Cu was lower in seeds but higher in old leaves of the quad-MT mutant compared to wild-type plants. Experiments with stable isotopes showed that Cu in seeds came from two sources: directly from roots and via remobilization from other organs. Mobilization of Cu out of senescing leaves was disrupted in MT-deficient plants. Tolerance to Cu, Zn and paraquat was unaffected by MT deficiency but these plants were slightly more sensitive to cadmium (Cd). The quad-MT mutant showed no change in resistance to a number of microbial pathogens, or in the progression of leaf senescence. Although these MTs are not required to complete the plant's life cycle, MTs are important for Cu homeostasis and distribution in Arabidopsis.

EgNRT2.3 and EgNAR2 expression are controlled by nitrogen deprivation and encode proteins that function as a two-component nitrate uptake system in oil palm.

Oil palm (Elaeis guineensis Jacq.) is an important crop for oil and biodiesel production. Oil palm plantations require extensive fertilizer additions to achieve a high yield. Fertilizer application decisions and management for oil palm farming rely on leaf tissue and soil nutrient analyses with little information available to describe the key players for nutrient uptake. A molecular understanding of how nutrients, especially nitrogen (N), are taken up in oil palm is very important to improve fertilizer use and formulation practice in oil palm plantations. In this work, two nitrate uptake genes in oil palm, EgNRT2.3 and EgNAR2, were cloned and characterized. Spatial expression analysis showed high expression of these two genes was mainly found in un-lignified young roots. Interestingly, EgNRT2.3 and EgNAR2 were up-regulated by N deprivation, but their expression pattern depended on the form of N source. Promoter analysis of these two genes confirmed the presence of regulatory elements that support these expression patterns. The Xenopus oocyte assay showed that EgNRT2.3 and EgNAR2 had to act together to take up nitrate. The results suggest that EgNRT2.3 and EgNAR2 act as a two-component nitrate uptake system in oil palm.