The miR164a-NAM3 module confers cold tolerance by inducing ethylene production in tomato.

Because of a high sensitivity to cold, both the yield and quality of tomato (Solanum lycopersicum L.) are severely restricted by cold stress. The NAC transcription factor (TF) family has been characterized as an important player in plant growth, development, and the stress response, but the role of NAC TFs in cold stress and their interaction with other post-transcriptional regulators such as microRNAs in cold tolerance remains elusive. Here, we demonstrated that SlNAM3, the predicted target of Sl-miR164a/b-5p, improved cold tolerance as indicated by a higher maximum quantum efficiency of photosystem II (Fv/Fm), lower relative electrolyte leakage, and less wilting in SlNAM3-overexpression plants compared to wild-type. Further genetic and molecular confirmation revealed that Sl-miR164a/b-5p functioned upstream of SlNAM3 by inhibiting the expression of the latter, thus playing a negative role in cold tolerance. Interestingly, this role is partially mediated by an ethylene-dependent pathway because either Sl-miR164a/b-5p silencing or SlNAM3 overexpression improved cold tolerance in the transgenic lines by promoting ethylene production. Moreover, silencing of the ethylene synthesis genes, SlACS1A, SlACS1B, SlACO1, and SlACO4, resulted in a significant decrease in cold tolerance. Further experiments demonstrated that NAM3 activates SlACS1A, SlACS1B, SlACO1, and SlACO4 transcription by directly binding to their promoters. Taken together, the present study identified the miR164a-NAM3 module conferring cold tolerance in tomato plants via the direct regulation of SlACS1A, SlACS1B, SlACO1, and SlACO4 expression to induce ethylene synthesis.

SEC1-C3H39 module fine-tunes cold tolerance by mediating its target mRNA degradation in tomato.

Plants adapt to cold stress at the physiological and biochemical levels, thus enabling them to maintain growth and development. However, the molecular mechanism of fine-tuning cold signals remains largely unknown. We addressed the function of SlSEC1-SlC3H39 module in cold tolerance by using SlSEC1 and SlC3H39 knockout and overexpression tomato lines. A tandem CCCH zinc-finger protein SlC3H39 negatively modulates cold tolerance in tomato. SlC3H39 binds to AU-rich elements in the 3'-untranslated region (UTR) to induce mRNA degradation and regulates gene expression post-transcriptionally. We further validate that SlC3H39 participates in post-transcriptional regulation of a variety of cold-responsive genes. An O-linked N-acetylglucosamine transferase SlSEC1 physically interacts with SlC3H39 proteins and negatively regulates cold tolerance in tomato. Further study shows that SlSEC1 is essential for SlC3H39 protein stability and maintains SlC3H39 function in cold tolerance. Genetic analysis shows that SlC3H39 is epistatic to SlSEC1 in cold tolerance. The findings indicate that SlC3H39 negatively modulates plant cold tolerance through post-transcriptional regulation by binding to cold-responding mRNA 3'-UTR and reducing those transcripts. SlSEC1 promotes the O-GlcNAclation status of SlC3H39 and maintains SlC3H39 function in cold tolerance. Taken together, we propose a SlSEC1-SlC3H39 module, which allows plants to balance defense responses and growth processes.