Endoplasmic reticulum stress response modulator OsbZIP39 regulates cadmium accumulation via activating the expression of defensin-like gene OsCAL2 in rice.

Accumulation of cadmium (Cd) in rice is not only harmful to the growth of plants but also poses a threat to human health. Exposure to Cd triggers unfolded protein response (UPR) within cells, a process that is still not completely understood. The study demonstrated that the lack of OsbZIP39, an essential endoplasmic reticulum (ER)-resident regulator of the UPR, resulted in decreased Cd intake and reduced Cd levels in the roots, stems, and grains of rice. Upon exposure to Cd stress, GFP-OsbZIP39 translocated from ER to nucleus, initiating UPR. Further investigation revealed that Cd treatment caused changes in sphingolipid levels in the membrane, influencing the localization and activation of OsbZIP39. Yeast one-hybrid and dual-LUC assays were conducted to validate the interaction between activated OsbZIP39 and the promoter of the defensin-like gene OsCAL2, resulting in an increase in its expression. Different variations were identified in the coding region of OsbZIP39, which may explain the varying levels of Cd accumulation observed in the indica and japonica subspecies. Under Cd treatment, OsbZIP39ind exhibited a more significant enhancement in the transcription of OsCAL2 compared to OsbZIP39jap. Our data suggest that OsbZIP39 positively regulates Cd uptake in rice, offering an encouraging objective for the cultivation of low-Cd rice.

PatWRKY71 transcription factor regulates patchoulol biosynthesis and plant defense response.

Patchoulol, a valuable compound belonging to the sesquiterpenoid family, is the primary component of patchouli oil produced by Pogostemon cablin (P. cablin). It has a variety of pharmacological and biological activities and is widely used in the medical and cosmetic industries. However, despite its significance, there is a lack of research on the transcriptional modulation of patchoulol biosynthesis.Salicylic acid (SA), is a vital plant hormone that serves as a critical signal molecule and plays an essential role in plant growth and defense. However, to date, no studies have explored the modulation of patchoulol biosynthesis by SA. In our study, we discovered that the application of SA can enhance the production of patchoulol. Utilizing transcriptome analysis of SA-treated P. cablin, we identified a crucial downstream transcription factor, PatWRKY71. The transcription level of PatWRKY71 was significantly increased with the use of SA. Furthermore, our research has revealed that PatWRKY71 was capable of binding to the promoter of PatPTS, ultimately leading to an increase in its expression. When PatWRKY71 was silenced by a virus, the expression of both PatWRKY71 and PatPTS was reduced, resulting in the down-regulation of patchoulol production. Through our studies, we discovered that heterologous expression of PatWRKY71 leads to an increase in the sensitivity of Arabidopsis to salt and Cd, as well as an outbreak of reactive oxygen species (ROS). Additionally, we uncovered the regulatory role of PatWRKY71 in both patchoulol biosynthesis and plant defense response. This discovery provided a theoretical basis for the improvement of the content of patchoulol and the resistance of P. cablin through genetic engineering.

Development and media regulate alternative splicing of a methyltransferase pre-mRNA in Monascus pilosus.

Two alternatively spliced mRNAs (d- and l-MpLaeA) of a methyltransferase gene (MpLaeA) were identified from Monascus pilosus IFO4520 and its mutant MK-1. Alternative splicing of the MpLaeA pre-mRNA occurred in the 5'-untranslated region (5'-UTR). The alternative splicing patterns of MpLaeA were regulated by the fungal growth stage and the principal nutrients: that is, the short l-MpLaeA mRNA was a constitutive transcript at all growth stages and different carbon or nitrogen sources, but the glutamate and NaNO(3) as main nitrogen source could up-regulate the long d-MpLaeA mRNA form. The long spliced 5'-UTR of d-MpLaeA blocked GFP expression in Escherichia coli , suggesting that d-MpLaeA mRNA was an ineffective spliced mRNA. Down-regulation of MpLaeA by transgenic antisense d-MpLaeA cDNA resulted in decreasing synthesis of monacolin K in M. pilosus. This suggested that the alternative splicing of MpLaeA mRNA might regulate the synthesis of monacolin K.

Repression of secondary metabolite production by exogenous cAMP in Monascus.

The cAMP signal pathway controls various biological functions, including secondary metabolism of filamentous fungi. We found that exogenous cAMP represses the production of lovastatin, red pigments, and citrinin in Monascus. Interestingly, a mutant MK-1 with increased lovastatin and red pigments production was not influenced by cAMP on these productions, indicating that cAMP signaling might be lacking in MK-1.

Effects of the principal nutrients on lovastatin production by Monascus pilosus.

Lovastatin production is dependent on the substrates provided. We investigated how several carbon and nitrogen sources in the medium affect lovastatin production by Monascus pilosus. M. pilosus required a suitable concentration of organic nitrogen peptone for high lovastatin production. As sole carbon source with peptone, although glucose strongly repressed lovastatin production, maltose was responsible for high production. Interestingly, glycerol combined with maltose enhanced lovastatin production, up to 444 mg/l in the most effective case. Moreover, an isolated mutant, in which glucose repression might be relieved, easily produced the highest level of lovastatin, 725 mg/l on glucose-glycerol-peptone medium. These observations indicate that lovastatin production by M. pilosus is regulated by strict glucose repression and that an appropriate release from this repression by optimizing medium composition and/or by a mutation(s) is required for high lovastatin production.

AtOPT6 transports glutathione derivatives and is induced by primisulfuron.

The oligopeptide transporter (OPT) family contains nine members in Arabidopsis. While there is some evidence that AtOPTs mediate the uptake of tetra- and pentapeptides, OPT homologs in rice (Oryza sativa; OsGT1) and Indian mustard (Brassica juncea; BjGT1) have been described as transporters of glutathione derivatives. This study investigates the possibility that two members of the AtOPT family, AtOPT6 and AtOPT7, may also transport glutathione and its conjugates. Complementation of the hgt1met1 yeast double mutant by plant homologs of the yeast glutathione transporter HGT1 (AtOPT6, AtOPT7, OsGT1, BjGT1) did not restore the growth phenotype, unlike complementation by HGT1. By contrast, complementation by AtOPT6 restored growth of the hgt1 yeast mutant on a medium containing reduced (GSH) or oxidized glutathione as the sole sulfur source and induced uptake of [3H]GSH, whereas complementation by AtOPT7 did not. In these conditions, AtOPT6-dependent GSH uptake in yeast was mediated by a high affinity (Km = 400 microm) and a low affinity (Km = 5 mm) phase. It was strongly competed for by an excess oxidized glutathione and glutathione-N-ethylmaleimide conjugate. Growth assays of yeasts in the presence of cadmium (Cd) suggested that AtOPT6 may transport Cd and Cd/GSH conjugate. Reporter gene experiments showed that AtOPT6 is mainly expressed in dividing areas of the plant (cambium, areas of lateral root initiation). RNA blots on cell suspensions and real-time reverse transcription-PCR on Arabidopsis plants indicated that AtOPT6 expression is strongly induced by primisulfuron and, to a lesser extent, by abscisic acid but not by Cd. Altogether, the data show that the substrate specificity and the physiological functions of AtOPT members may be diverse. In addition to peptide transport, AtOPT6 is able to transport glutathione derivatives and metal complexes, and may be involved in stress resistance.

A novel family of transporters mediating the transport of glutathione derivatives in plants.

Uptake and compartmentation of reduced glutathione (GSH), oxidized glutathione (GSSG), and glutathione conjugates are important for many functions including sulfur transport, resistance against biotic and abiotic stresses, and developmental processes. Complementation of a yeast (Saccharomyces cerevisiae) mutant (hgt1) deficient in glutathione transport was used to characterize a glutathione transporter cDNA (OsGT1) from rice (Oryza sativa). The 2.58-kb full-length cDNA (AF393848, gi 27497095), which was obtained by screening of a cDNA library and 5'-rapid amplification of cDNA ends-polymerase chain reaction, contains an open reading frame encoding a 766-amino acid protein. Complementation of the hgt1 yeast mutant strain with the OsGT1 cDNA restored growth on a medium containing GSH as the sole sulfur source. The strain expressing OsGT1 mediated [3H]GSH uptake, and this uptake was significantly competed not only by unlabeled GSSG and GS conjugates but also by some amino acids and peptides, suggesting a wide substrate specificity. OsGT1 may be involved in the retrieval of GSSG, GS conjugates, and nitrogen-containing peptides from the cell wall.