The regeneration factors ERF114 and ERF115 regulate auxin-mediated lateral root development in response to mechanical cues.

Plants show an unparalleled regenerative capacity, allowing them to survive severe stress conditions, such as injury, herbivory attack, and harsh weather conditions. This potential not only replenishes tissues and restores damaged organs but can also give rise to whole plant bodies. Despite the intertwined nature of development and regeneration, common upstream cues and signaling mechanisms are largely unknown. Here, we demonstrate that in addition to being activators of regeneration, ETHYLENE RESPONSE FACTOR 114 (ERF114) and ERF115 govern developmental growth in the absence of wounding or injury. Increased ERF114 and ERF115 activity enhances auxin sensitivity, which is correlated with enhanced xylem maturation and lateral root formation, whereas their knockout results in a decrease in lateral roots. Moreover, we provide evidence that mechanical cues contribute to ERF114 and ERF115 expression in correlation with BZR1-mediated brassinosteroid signaling under both regenerative and developmental conditions. Antagonistically, cell wall integrity surveillance via mechanosensory FERONIA signaling suppresses their expression under both conditions. Taken together, our data suggest a molecular framework in which cell wall signals and mechanical strains regulate organ development and regenerative responses via ERF114- and ERF115-mediated auxin signaling.

Abscisic acid signaling activates distinct VND transcription factors to promote xylem differentiation in Arabidopsis.

Plants display remarkable abilities to adjust growth and development to environmental conditions, such as the amount of available water. This developmental plasticity is apparent not only in root and shoot growth rates, but also in tissue patterning and cell morphology.1,2 We have previously shown that in response to limited water availability, Arabidopsis thaliana root displays changes in xylem morphology, mediated by the non-cell-autonomous action of abscisic acid, ABA.2 Here, we show, through analyses of ABA response reporters and tissue-specific suppression of ABA signaling, that xylem cells themselves act as primary signaling centers governing both xylem cell fate and xylem differentiation rate, revealing the cell-autonomous control of multiple aspects of xylem development by ABA. ABA rapidly activates the expression of genes encoding VASCULAR-RELATED NAC DOMAIN (VND) transcription factors. Molecular and genetic analyses revealed that the two ABA-mediated xylem developmental changes are regulated by distinct members of this transcription factor family, with VND2 and VND3 promoting differentiation rate of metaxylem cells, while VND7 promotes the conversion of metaxylem toward protoxylem morphology. This phenomenon shows how different aspects of developmental plasticity can be interlinked, yet genetically separable. Moreover, similarities in phenotypic and molecular responses to ABA in diverse species indicate evolutionary conservation of the ABA-xylem development regulatory network among eudicots. Hence, this study gives molecular insights into how environmental stress modifies plant vascular anatomy and has potential relevance for water use optimization and adaptation to drought conditions.

CRISPR: From Prokaryotic Immune Systems to Plant Genome Editing Tools.

The clustered regularly interspaced short palindromic repeats (CRISPR) system is a prokaryotic adaptive immune system that has the ability to identify specific locations on the bacteriophage (phage) genome to create breaks in it, and internalize the phage genome fragments in its own genome as CRISPR arrays for memory-dependent resistance. Although CRISPR has been used in the dairy industry for a long time, it recently gained importance in the field of genome editing because of its ability to precisely target locations in a genome. This system has further been modified to locate and target any region of a genome of choice due to modifications in the components of the system. By changing the nucleotide sequence of the 20-nucleotide target sequence in the guide RNA, targeting any location is possible. It has found an application in the modification of plant genomes with its ability to generate mutations and insertions, thus helping to create new varieties of plants. With the ability to introduce specific sequences into the plant genome after cleavage by the CRISPR system and subsequent DNA repair through homology-directed repair (HDR), CRISPR ensures that genome editing can be successfully applied in plants, thus generating stronger and more improved traits. Also, the use of the CRISPR editing system can generate plants that are transgene-free and have mutations that are stably inherited, thus helping to circumvent current GMO regulations.

CRISPR-Cas9 and CRISPR-Cpf1 mediated targeting of a stomatal developmental gene EPFL9 in rice.

KEY MESSAGE: CRISPR-Cas9/Cpf1 system with its unique gene targeting efficiency, could be an important tool for functional study of early developmental genes through the generation of successful knockout plants. The introduction and utilization of systems biology approaches have identified several genes that are involved in early development of a plant and with such knowledge a robust tool is required for the functional validation of putative candidate genes thus obtained. The development of the CRISPR-Cas9/Cpf1 genome editing system has provided a convenient tool for creating loss of function mutants for genes of interest. The present study utilized CRISPR/Cas9 and CRISPR-Cpf1 technology to knock out an early developmental gene EPFL9 (Epidermal Patterning Factor like-9, a positive regulator of stomatal development in Arabidopsis) orthologue in rice. Germ-line mutants that were generated showed edits that were carried forward into the T2 generation when Cas9-free homozygous mutants were obtained. The homozygous mutant plants showed more than an eightfold reduction in stomatal density on the abaxial leaf surface of the edited rice plants. Potential off-target analysis showed no significant off-target effects. This study also utilized the CRISPR-LbCpf1 (Lachnospiracae bacterium Cpf1) to target the same OsEPFL9 gene to test the activity of this class-2 CRISPR system in rice and found that Cpf1 is also capable of genome editing and edits get transmitted through generations with similar phenotypic changes seen with CRISPR-Cas9. This study demonstrates the application of CRISPR-Cas9/Cpf1 to precisely target genomic locations and develop transgene-free homozygous heritable gene edits and confirms that the loss of function analysis of the candidate genes emerging from different systems biology based approaches, could be performed, and therefore, this system adds value in the validation of gene function studies.