Secondary cell wall thickening plays a crucial role in plant growth and development. Diploid woodland strawberry (Fragaria vesca) is an excellent model for studying fruit development, but its molecular control of secondary wall thickening is largely unknown. Previous studies have shown that Arabidopsis NAC secondary wall thickening promoting factor1 (AtNST1) and related proteins are master regulators of xylem fiber cell differentiation in multiple plant species. In this study, a NST1-like gene, FvNST1b, was isolated and characterized from strawberry. Sequence alignment and phylogenetic analysis showed that the FvNST1b protein contains a highly conserved NAC domain, and it belongs to the same family as AtNST1. Overexpression of FvNST1b in wild-type Arabidopsis caused extreme dwarfism, induced ectopic thickening of secondary walls in various tissues, and upregulated the expression of genes related to secondary cell wall synthesis. In addition, transient overexpression of FvNST1b in wild-type Fragaria vesca fruit produced cells resembling tracheary elements. These results suggest that FvNST1b positively regulates secondary cell wall formation as orthologous genes from other species.

Small GTPases act as molecular switches that regulate various plant responses such as disease resistance, pollen tube growth, root hair development, cell wall patterning and hormone responses. Thus, to monitor their activation status within plant cells is believed to be the key step in understanding their roles. We have established a plant version of a Förster resonance energy transfer (FRET) probe called Ras and interacting protein chimeric unit (Raichu) that can successfully monitor activation of the rice small GTPase OsRac1 during various defence responses in cells. Here, we describe the protocol for visualizing spatiotemporal activity of plant Rac/ROP GTPase in living plant cells, transfection of rice protoplasts with Raichu-OsRac1 and acquisition of FRET images. Our protocol should be adaptable for monitoring activation for other plant small GTPases and protein–protein interactions for other FRET sensors in various plant cells.

Leaves evolve shape diversity ranging from simple leaves with smooth margin to complicated shape with toothed/serrated, lobed and dissected leaves with leaflets. In the model plant Arabidopsis thaliana with simple leaves producing serrated margin, boundary regulatory factors CUP SHAPED COTYLEDON 2 (CUC2) and CUC3 play important roles in promoting leaf serration initiation and maintenance. Stem cell related WUSCHEL-RELATED HOMEOBOX1 (WOX1) and PRESSED FLOWER/WOX3 are also essential for leaf margin morphogenesis, but the role of WOX1 and PRS as well as the relationships between CUCs and WOXs on tooth development was unclear. In this study, we found that WOX1, but not PRS, prevents overproduction of tooth number and excessive tooth size by limiting CUC3 expression to a moderate level in a temporally regulated manner. We also revealed that BRASSINAZOLE RESISTANT 1 (BZR1), a known regulator for plant development including boundary regions, is involved in WOX1 negative regulation of tooth development by repressing CUC3 expression during the initiation/early stage of tooth development. WOX1 parallelly limits BZR1 and CUC3 expression from the late stage of the first 2 teeth, while restricts CUC3 activity in a BZR1 dependent manner from the initiation/early stage of subsequently developed teeth. This study uncovers a new mechanism for WOX1 in fine-tuning the leaf margin geometry.

Secondary cell wall (SCW) thickening has a significant effect on the growth and development of plants, as well as in the resistance to various biotic and abiotic stresses. Lignin accounts for the strength of SCW. It is synthesized through the phenylpropanoid pathway that also leads to flavonoid synthesis. The coupling strategies for lignin and flavonoid syntheses are diverse in plants. How their syntheses are balanced by transcriptional regulation in fleshy fruits is still unclear. The diploid strawberry (Fragaria vesca) is a model for fleshy fruits research due to its small genome and wide scope of genetic transformation. SCW thickening is regulated by a multilevel transcriptional regulatory network wherein vascular-related NAC domains (VNDs) act as key regulators. In this study, we systematically characterized VNDs in Fragaria vesca and explored their functions. The overexpression of FvVND4c in diploid strawberry fruits resulted in SCW thickening and fruit color changes accompanied with the accumulation of lignin and flavonoids. Genes related to these phenotypes were also induced upon FvVND4c overexpression. Among the induced genes, we found FvMYB46 to be a direct downstream regulator of FvVND4c. The overexpression of FvMYB46 resulted in similar phenotypes as FvVND4c, except for the color change. Transcriptomic analyses suggest that both FvVND4c and FvMYB46 act on phenylpropanoid and flavonoid biosynthesis pathways, and induce lignin synthesis for SCW. These results suggest that FvVND4c and FvMYB46 cooperatively regulate SCW thickening and flavonoid accumulation in Fragaria vesca.

Highly differentiated tissues and organs play essential biological functions in multicellular organisms. Coordination of organ developmental process with tissue differentiation is necessary to achieve proper development of mature organs, but mechanisms for such coordination are not well understood. We used cotyledon margin cells from Arabidopsis plant as a new model system to investigate cell elongation and cell division during organ growth and found that margin cells endured a developmental phase transition from the “elongation” phase to the “elongation and division” phase at the early stage in germinating seedlings. We also discovered that the stem cell factors BARELY ANY MERISTEM 1 (BAM1) and WUSCHEL-related homeobox1 (WOX1) are involved in the regulation of margin cell developmental phase transition. Furthermore, exogenous auxin treatment (1 nanomolar,nM) promotes cell division, especially longitudinal cell division. This promotion of cell division did not occur in bam1 and wox1 mutants. Based on these findings, we hypothesized a new “moderate auxin concentration” model which emphasizes that a moderate auxin concentration is the key to triggering the developmental transition of meristematic cells.

RNA interference (RNAi) in plants can move from cell to cell, allowing for systemic spread of an anti-viral immune response. How this cell-to-cell spread of silencing is regulated is currently unknown. Here, we describe that the C4 protein from Tomato yellow leaf curl virus has the ability to inhibit the intercellular spread of RNAi. Using this viral protein as a probe, we have identified the receptor-like kinase (RLK) BARELY ANY MERISTEM 1 (BAM1) as a positive regulator of the cell-to-cell movement of RNAi, and determined that BAM1 and its closest homologue, BAM2, play a redundant role in this process. C4 interacts with the intracellular domain of BAM1 and BAM2 at the plasma membrane and plasmodesmata, the cytoplasmic connections between plant cells, interfering with the function of these RLKs in the cell-to-cell spread of RNAi. Our results identify BAM1 as an element required for the cell-to-cell spread of RNAi and highlight that signalling components have been co-opted to play multiple functions in plants.