Nucleotide composition is suggested to infer gene functionality and ecological adaptation of species to distinct environments. However, the underlying biological function of nucleotide composition dictating environmental adaptations is largely unknown. Here, we systematically analyze the nucleotide composition of transcriptomes across 1000 plants (1KP) and their corresponding habitats. Intriguingly, we find that plants growing in cold climates have guanine (G)-enriched transcriptomes, which are prone to forming RNA G-quadruplex structures. Both immunofluorescence detection and in vivo structure profiling reveal that RNA G-quadruplex formation in plants is globally enhanced in response to cold. Cold-responsive RNA G-quadruplexes strongly enhanced mRNA stability, rather than affecting translation. Disruption of individual RNA G-quadruplex promotes mRNA decay in the cold, leading to impaired plant cold response. Therefore, we propose that plants adopted RNA G-quadruplex structure as a molecular signature to facilitate their adaptation to the cold during evolution.

Cu2+ ions are required by all living organisms and play important roles in many bactericides and fungicides. We previously reported that Cu2+ can elicit defense responses, which are dependent on the ethylene signaling pathway in Arabidopsis. However, the mechanism by which Cu2+ elicits the biosynthesis of ethylene remains unclear. Here, we show that CuSO4 treatment rapidly increases the production of ethylene. In addition, it upregulates the expression of several defense-related genes and ethylene biosynthesis genes, including genes encoding S-adenosylmethionine synthase, 1-aminocyclopropane-1-carboxylate (ACC) synthase (ACS) and ACC oxidase. Among these genes, Arabidopsis thaliana (At)ACS8 was identified as essential for the defense response and early ethylene biosynthesis induced by Cu2+. Furthermore, Cu2+-induced AtACS8 expression depended on the copper-response cis-element (CuRE) in the promoter of AtACS8. Our study indicates that Cu2+ specifically activates the expression of AtACS8 to promote the early biosynthesis of ethylene that elicits plant immunity in Arabidopsis plants.

Copper (Cu)-based antimicrobial compounds (CBACs) have been widely used to control phytopathogens for nearly fourteen decades. Since the first commercialized Bordeaux mixture was introduced, CBACs have been gradually developed from highly to slightly soluble reagents and from inorganic to synthetic organic, with nanomaterials being a recent development. Traditionally, slightly soluble CBACs form a physical film on the surface of plant tissues, separating the micro-organisms from the host, then release divalent or monovalent copper ions (Cu²⁺ or Cu⁺) to construct a secondary layer of protection which inhibits the growth of pathogens. Recent progress has demonstrated that the release of a low concentration of Cu²⁺ may elicit immune responses in plants. This supports a triple-tiered protection role of CBACs: break contact, inhibit microorganisms, and stimulate host immunity. This spatial defense system, which is integrated both inside and outside the plant cell, provides long-lasting and broad-spectrum protection, even against emergent copper-resistant strains. Here, we review recent findings and highlight the perspectives underlying mitigation strategies for the sustainable utilization of CBACs.

Xanthomonas oryzae delivers transcription activator-like effectors (TALEs) into plant cells to facilitate infection. Following economic principles, the redundant TALEs are rarely identified in Xanthomonas. Previously, we identified the Tal2b, which activates the expression of the rice 2-oxoglutarate-dependent dioxygenase gene OsF3H_03g to promote infection in the highly virulent strain of X. oryzae pv. oryzicola HGA4. Here, we reveal that another clustered TALE, Tal2c, also functioned as a virulence factor to target rice OsF3H_04g, a homologue of OsF3H_03g. Transferring Tal2c into RS105 induced expression of OsF3H_04g to coincide with increased susceptibility in rice. Overexpressing OsF3H_04g caused higher susceptibility and less salicylic acid (SA) production compared to wild-type plants. Moreover, CRISPR–Cas9 system-mediated editing of the effector-binding element in the promoters of OsF3H_03g or OsF3H_04g was found to specifically enhance resistance to Tal2b- or Tal2c-transferring strains, but had no effect on resistance to either RS105 or HGA4. Furthermore, transcriptome analysis revealed that several reported SA-related and defense-related genes commonly altered expression in OsF3H_04g overexpression line compared with those identified in OsF3H_03g overexpression line. Overall, our results reveal a functional redundancy mechanism of pathogenic virulence in Xoc in which tandem Tal2b and Tal2c specifically target homologues of host genes to interfere with rice immunity by reducing SA.