Switching action modes of miR408-5p mediates auxin signaling in rice.

MicroRNAs (miRNAs) play fundamental roles in many developmental and physiological processes in eukaryotes. MiRNAs in plants generally regulate their targets via either mRNA cleavage or translation repression; however, which approach plays a major role and whether these two function modes can shift remains elusive. Here, we identify a miRNA, miR408-5p that regulates AUXIN/INDOLE ACETIC ACID 30 (IAA30), a critical repressor in the auxin pathway via switching action modes in rice. We find that miR408-5p usually inhibits IAA30 protein translation, but in a high auxin environment, it promotes the decay of IAA30 mRNA when it is overproduced. We further demonstrate that IDEAL PLANT ARCHITECTURE1 (IPA1), an SPL transcription factor regulated by miR156, mediates leaf inclination through association with miR408-5p precursor promoter. We finally show that the miR156-IPA1-miR408-5p-IAA30 module could be controlled by miR393, which silences auxin receptors. Together, our results define an alternative auxin transduction signaling pathway in rice that involves the switching of function modes by miR408-5p, which contributes to a better understanding of the action machinery as well as the cooperative network of miRNAs in plants.

Cadmium induced a non-coding RNA microRNA535 mediates Cd accumulation in rice.

Identifying key regulators related to cadmium (Cd) tolerance and accumulation is the main factor for genetic engineering to improve plants for bioremediation and ensure crop food safety. MicroRNAs (miRNAs), as fine-tuning regulators of genes, participate in various abiotic stress processes. MiR535 is an ancient conserved non-coding small RNA in land plants, positively responding to Cd stress. We investigated the effects of knocking out (mir535) and overexpressing miR535 (mir535 and OE535) under Cd stress in rice plants in this study. The mir535 plants showed better Cd tolerance than wild type (WT), whereas the OE535 showed the opposite effect. Cd accumulated approximately 71.9% and 127% in the roots of mir535 and OE535 plants, respectively, compared to WT, after exposure to 2 µmol/L Cd. In brown rice, the total Cd accumulation of OE535 and mir535 was about 78% greater and 35% lower than WT. When growing in 2 mg/kg Cd of soil, the Cd concentration was significantly lower in mir535 and higher in OE535 than in the WT; afterward, we further revealed the most possible target gene SQUAMOSA promoter binding-like transcription factor 7(SPL7) and it negatively regulates Nramp5 expression, which in turn regulates Cd metabolism. Therefore, the CRISPR/Cas9 technology may be a valuable strategy for creating new rice varieties to ensure food safety.

A mutation in class III homeodomain-leucine zipper (HD-ZIP III) transcription factor results in curly leaf (cul) in cucumber (Cucumis sativus L.).

KEY MESSAGE: We identified two curly-leaf (cul) mutants in cucumber. Map-based cloning revealed that both mutants are due to allelic mutations in the CsPHB gene, a homolog of the Arabidopsis PHABULOSA which encodes a class III homeodomain-leucine zipper (HD-ZIP III) transcription factor. Leaf rolling is an important agronomic trait in crop breeding. Moderate leaf rolling minimizes shadowing between leaves, leading to improved photosynthetic efficiency. Although a number of genes controlling rolled leaf have been identified from rice and other plant species, none have been mapped or cloned in cucurbit crops. In this study, we identified and characterized two curly leaf (cul) mutants, cul-1 and cul-2 in cucumber. With map-based cloning, we show that cul-1 and cul-2 are allelic mutations and CsPHB (Csa6G525430) was the candidate gene for both mutants. The CsPHB gene encoded a class III homeodomain-leucine zipper (HD-ZIP III) transcription factor. A single non-synonymous mutation in the fourth and fifth exons of the CsPHB was responsible for the cul-1 and cul-2 mutant phenotypes, respectively. The single-nucleotide substitutions in cul-1 and cul-2 were both located in cs-miRNA165/166 complementary sites of CsPHB. The expression level of CsPHB gene in multiple organs of cul-1 and cul-2 mutants was higher than that in the wild type, while the expression of cs-miRNA165/166 in the two genotypes showed the opposite trend. We speculate that disruption of the binding between the mutant allele of CsPHB and cs-miRNA165/166 leads to the curly-leaf phenotype. This is the first report to clone and characterize the CsPHB gene in the family Cucurbitaceae. Taken together, these results support CsPHB as an important player in the modulation of leaf shape development in cucumber.