Redox signaling mediates the expression of a sulfate‐deprivation‐inducible microRNA395 in Arabidopsis

MicroRNA395 (miR395) is a conserved miRNA that targets a low‐affinity sulfate transporter (AST68) and three ATP sulfurylases (APS1, APS3 and APS4) in higher plants. In this study, At2g28780 was confirmed as another target of miR395 in Arabidopsis. Interestingly, several dicots contained genes homologous to At2g28780 and a cognate miR395 complementary site but possess a gradient of mismatches at the target site. It is well established that miR395 is induced during S deprivation in Arabidopsis; however, the signaling pathways that mediate this regulation are unknown. Several findings in the present study demonstrate that redox signaling plays an important role in induction of miR395 during S deprivation. These include the following results: (i) glutathione (GSH) supplementation suppressed miR395 induction in S‐deprived plants (ii) miR395 is induced in Arabidopsis seedlings exposed to Arsenate or Cu²⁺, which induces oxidative stress (iii), S deprivation‐induced oxidative stress, and (iv) compromised induction of miR395 during S deprivation in cad2 mutant (deficient in GSH biosynthesis) that is defective in glutaredoxin‐dependent redox signaling and ntra/ntrb (defective in thioredoxin reductases a and b) double mutants that are defective in thioredoxin‐dependent redox signaling. Collectively, these findings strongly support the involvement of redox signaling in inducing the expression of miR395 during S deprivation in Arabidopsis.     

Gene mining in halophytes: functional identification of stress tolerance genes in Lepidium crassifolium

Extremophile plants are valuable sources of genes conferring tolerance traits, which can be explored to improve stress tolerance of crops. Lepidium crassifolium is a halophytic relative of the model plant Arabidopsis thaliana, and displays tolerance to salt, osmotic and oxidative stresses. We have employed the modified Conditional cDNA Overexpression System to transfer a cDNA library from L. crassifolium to the glycophyte A. thaliana. By screening for salt, osmotic and oxidative stress tolerance through in vitro growth assays and non‐destructive chlorophyll fluorescence imaging, 20 Arabidopsis lines were identified with superior performance under restrictive conditions. Several cDNA inserts were cloned and confirmed to be responsible for the enhanced tolerance by analysing independent transgenic lines. Examples include full‐length cDNAs encoding proteins with high homologies to GDSL‐lipase/esterase or acyl CoA‐binding protein or proteins without known function, which could confer tolerance to one or several stress conditions. Our results confirm that random gene transfer from stress tolerant to sensitive plant species is a valuable tool to discover novel genes with potential for biotechnological applications.