Plants strictly regulate the uptake and distribution of Zn, which is essential for plant growth and development. Here, we show that Arabidopsis thaliana PCR2 is essential for Zn redistribution and Zn detoxification. The pcr2 loss-of-function mutant was compromised in growth, both in Zn-excessive and -deficient conditions. The roots of pcr2 accumulated more Zn than did control plants, whereas the roots of plants overexpressing PCR2 contained less Zn, indicating that PCR2 removes Zn from the roots. Consistent with a role for PCR2 as a Zn-efflux transporter, PCR2 reduced the intracellular concentration of Zn when expressed in yeast cells. PCR2 is located mainly in epidermal cells and in the xylem of young roots, while it is expressed in epidermal cells in fully developed roots. Zn accumulated in the epidermis of the roots of pcr2 grown under Zn-limiting conditions, whereas it was found in the stele of wild-type roots. The transport pathway mediated by PCR2 does not seem to overlap with that mediated by the described Zn translocators (HMA2 and HMA4) since the growth of pcr2 hma4 double and pcr2 hma2 hma4 triple loss-of-function mutants was more severely inhibited than the individual single knockout mutants, both under conditions of excess or deficient Zn. We propose that PCR2 functions as a Zn transporter essential for maintaining an optimal Zn level in Arabidopsis.

This work demonstrates that structural defects in amorphous metal oxide electrodes can serve as a reversible Li+ storage site for lithium secondary batteries. For instance, molybdenum dioxide electrode in amorphous form (a‐MoO2) exhibits an unexpectedly high Li+ storage capacity (up to four Li per MoO2 unit), which is larger by a factor of four than that for the crystalline counterpart. The conversion‐type lithiation is discarded for this electrode from the absence of Mo metal and lithium oxide (Li2O) in the lithiated a‐MoO2 electrode and the retention of local structural framework. The sloping voltage profile in a wide potential range suggests that Li+ ions are inserted into the structural defects that are electrochemically nonequivalent. This electrode also shows an excellent cycle stability and rate capability. The latter feature is seemingly due to a rather opened Li+ diffusion pathway provided by the structural defects. A high Li+ mobility is confirmed from nuclear magnetic resonance study.

Carotenoids have essential roles in light-harvesting processes and protecting the photosynthetic machinery from photo-oxidative damage. Phytoene synthase (PSY) and Orange (Or) are key plant proteins for carotenoid biosynthesis and accumulation. We previously isolated the sweetpotato (Ipomoea batatas) Or gene (IbOr), which is involved in carotenoid accumulation and salt stress tolerance. The molecular mechanism underlying IbOr regulation of carotenoid accumulation was unknown. Here, we show that IbOr has an essential role in regulating IbPSY stability via its holdase chaperone activity both in vitro and in vivo. This protection results in carotenoid accumulation and abiotic stress tolerance. IbOr transcript levels increase in sweetpotato stem, root, and calli after exposure to heat stress. IbOr is localized in the nucleus and chloroplasts, but interacts with IbPSY only in chloroplasts. After exposure to heat stress, IbOr predominantly localizes in chloroplasts. IbOr overexpression in transgenic sweetpotato and Arabidopsis conferred enhanced tolerance to heat and oxidative stress. These results indicate that IbOr holdase chaperone activity protects IbPSY stability, which leads to carotenoid accumulation, and confers enhanced heat and oxidative stress tolerance in plants. This study provides evidence that IbOr functions as a molecular chaperone, and suggests a novel mechanism regulating carotenoid accumulation and stress tolerance in plants.

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Lycopene ε-cyclase (LCY-ε) is involved in the first step of the α-branch synthesis pathway of carotenoids from lycopene in plants. In this study, to enhance carotenoid synthesis via the β-branch-specific pathway [which yields β-carotene and abscisic acid (ABA)] in sweet potato, the expression of IbLCY-ε was downregulated by RNAi (RNA interference) technology. The RNAi-IbLCY-ε vector was constructed using a partial cDNA of sweet potato LCY-ε isolated from the storage root and introduced into cultured sweet potato cells by Agrobacterium-mediated transformation. Both semi-quantitative Reverse transcription polymerase chain reaction (RT-PCR) of carotenoid biosynthesis genes and high-performance liquid chromatography (HPLC) analysis of the metabolites in transgenic calli, in which the LCY- εgene was silenced, showed the activation of β-branch carotenoids and its related genes. In the transgenic calli, the β-carotene content was approximately 21-fold higher than in control calli, whereas the lutein content of the transgenic calli was reduced to levels undetectable by HPLC. Similarly, expression of the RNAi-IbLCY-ε transgene resulted in a twofold increase in ABA content compared to control calli. The transgenic calli showed significant tolerance of 200 mM NaCl. Furthermore, both the β-branch carotenoids content and the expression levels of various branch-specific genes were higher under salt stress than in control calli. These results suggest that, in sweet potato, downregulation of the ε-cyclization of lycopene increases carotenoid synthesis via the β-branch-specific pathway and may positively regulate cellular defenses against salt-mediated oxidative stress.

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R2R3-type MYB transcription factors (TFs) play important roles in transcriptional regulation of anthocyanins. The R2R3-type IbMYB1 is known to be a key regulator of anthocyanin biosynthesis in the storage roots of sweetpotato. We previously showed that transient expression of IbMYB1a led to anthocyanin pigmentation in tobacco leaves. In this article, we generated transgenic Arabidopsis plants expressing the IbMYB1a gene under the control of CaMV 35S promoter, and the sweetpotato SPO and SWPA2 promoters. Overexpression of IbMYBa in transgenic Arabidopsis produced strong anthocyanin pigmentation in seedlings and generated a deep purple color in leaves, stems and seeds. Reverse transcription-polymerase chain reaction analysis showed that IbMYB1a expression induced upregulation of several structural genes in the anthocyanin biosynthetic pathway, including 4CL, CHI, F3'H, DFR, AGT, AAT and GST. Furthermore, overexpression of IbMYB1a led to enhanced expression of the AtTT8 (bHLH) and PAP1/AtMYB75 genes. high-performance liquid chromatography analysis revealed that IbMYB1a expression led to the production of cyanidin as a major core molecule of anthocyanidins in Arabidopsis, as occurs in the purple leaves of sweetpotato (cv. Sinzami). This result shows that the IbMYB1a TF is sufficient to induce anthocyanin accumulation in seedlings, leaves, stems and seeds of Arabidopsis plants.