Exogenous RNAs: promising tools for the second green revolution.

The impending need for increasing amounts of food for the world population poses enormous challenges to agriculture. Moreover, global warming has exacerbated abiotic and biotic stresses, accelerating the emergence of new pests and pathogens which threatens crop productivity. Therefore, the scientific community urgently needs to develop innovative solutions for sustainable agriculture, notably replacing synthetic pesticides by active and highly specific biomolecules for pest control. In this context, RNA-based technologies emerge as an outstanding genetically modified organism-free approach offering versatile solutions to boost productivity while conserving and harnessing the wide variety of local landraces. Here we review recent advances in the field, including RNA synthesis approaches and the development of the nanotechnology required for RNA stabilization and delivery, and we discuss the potential of RNA as the key molecule for versatile applications in the second green revolution.

The lncRNA APOLO interacts with the transcription factor WRKY42 to trigger root hair cell expansion in response to cold.

Plant long noncoding RNAs (lncRNAs) have emerged as important regulators of chromatin dynamics, impacting on transcriptional programs leading to different developmental outputs. The lncRNA AUXIN-REGULATED PROMOTER LOOP (APOLO) directly recognizes multiple independent loci across the Arabidopsis genome and modulates their three-dimensional chromatin conformation, leading to transcriptional shifts. Here, we show that APOLO recognizes the locus encoding the root hair (RH) master regulator ROOT HAIR DEFECTIVE 6 (RHD6) and controls RHD6 transcriptional activity, leading to cold-enhanced RH elongation through the consequent activation of the transcription factor gene RHD6-like RSL4. Furthermore, we demonstrate that APOLO interacts with the transcription factor WRKY42 and modulates its binding to the RHD6 promoter. WRKY42 is required for the activation of RHD6 by low temperatures and WRKY42 deregulation impairs cold-induced RH expansion. Collectively, our results indicate that a novel ribonucleoprotein complex with APOLO and WRKY42 forms a regulatory hub to activate RHD6 by shaping its epigenetic environment and integrate signals governing RH growth and development.

Evolution of the Small Family of Alternative Splicing Modulators Nuclear Speckle RNA-binding Proteins in Plants.

RNA-Binding Protein 1 (RBP1) was first identified as a protein partner of the long noncoding RNA (lncRNA) ENOD40 in Medicagotruncatula, involved in symbiotic nodule development. RBP1 is localized in nuclear speckles and can be relocalized to the cytoplasm by the interaction with ENOD40. The two closest homologs to RBP1 in Arabidopsis thaliana were called Nuclear Speckle RNA-binding proteins (NSRs) and characterized as alternative splicing modulators of specific mRNAs. They can recognize in vivo the lncRNA ALTERNATIVE SPLICING COMPETITOR (ASCO) among other lncRNAs, regulating lateral root formation. Here, we performed a phylogenetic analysis of NSR/RBP proteins tracking the roots of the family to the Embryophytes. Strikingly, eudicots faced a reductive trend of NSR/RBP proteins in comparison with other groups of flowering plants. In Medicagotruncatula and Lotus japonicus, their expression profile during nodulation and in specific regions of the symbiotic nodule was compared to that of the lncRNA ENOD40, as well as to changes in alternative splicing. This hinted at distinct and specific roles of each member during nodulation, likely modulating the population of alternatively spliced transcripts. Our results establish the basis to guide future exploration of NSR/RBP function in alternative splicing regulation in different developmental contexts along the plant lineage.