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Summary Adventitious root initiation (ARI) is a de novo organogenesis program and a key adaptive trait in plants. Several hormones regulate ARI but the underlying genetic architecture that integrates the hormonal crosstalk governing this process remains largely elusive. In this study, we use genetics, genome editing, transcriptomics, hormone profiling and cell biological approaches to demonstrate a crucial role played by the APETALA2/ETHYLENE RESPONSE FACTOR 115 transcription factor. We demonstrate that ERF115 functions as a repressor of ARI by activating the cytokinin (CK) signaling machinery. We also demonstrate that ERF115 is transcriptionally activated by jasmonate (JA), an oxylipin‐derived phytohormone, which represses ARI in NINJA‐dependent and independent manners. Our data indicate that NINJA‐dependent JA signaling in pericycle cells blocks early events of ARI. Altogether, our results reveal a previously unreported molecular network involving cooperative crosstalk between JA and CK machineries that represses ARI.

34Jasmonate (JA), an oxylipin-derived phytohormone, plays crucial roles not only in plant 35 immunity and defense against herbivorous insects but also in plant growth and developmental 36 processes, including regeneration and organogenesis. However, the mechanistic basis of its 37 mode of action and precise role in integrating other signaling cues are poorly understood. Here 38 we provide genetic indications that JA signaling acts in both NINJA-dependent and -39 independent modulation of the transcriptional activity of MYC transcription factors involved 40 in the inhibition of adventitious root initiation (ARI). Our data show that NINJA-dependent JA 41 signaling in pericycle cells blocks early events of ARI. Moreover, transcriptomic comparison 42 of ninja-1myc2-322B double mutant (which produce extremely few ARs) and wild type 43 seedlings identified a novel molecular network governed by the APETALA2/ETHYLENE 44 RESPONSE FACTOR 115 (ERF115) transcription factor. We demonstrate that JA-induced 45 ERF115 activates the cytokinin signaling machinery and thereby represses ARI. Altogether, 46 our results reveal a molecular network involving cooperative crosstalk between JA and CK 47 machineries that inhibits ARI. 48 49 Key words: 50 Jasmonate, cytokinins, adventitious rooting, AP2/ERF transcription factors, de novo 51 organogenesis. 52 53 Jasmonate (JA), a stress-induced phytohormone, plays crucial roles in plant immunity and 54 defense against herbivorous insects (Wasternack and Hause, 2013). It also participates in 55 control of diverse developmental processes, including tissue regeneration and rhizotaxis 56 (Wasternack and Hause, 2013;Lakehal et al., 2020). The isomer (+)-7-iso-JA-Ile (JA-Ile), the 57 bioactive form of JA (Fonseca et al., 2009), is perceived by the F-box protein CORONATINE 58 INSENSITIVE1 (COI1), which is an integral component of the Skp-Cullin-F-box (SCF) 59 complex (Xie et al., 1998). The COI1 receptor fine-tunes the function of the JA transcriptional 60 machinery in a simple manner. Briefly, in the resting state, marked by low JA-Ile contents, the 61 transcriptional activity of a number of transcription factors, including the basic-Helix-loop-62 Helix MYC, is repressed by JASMONATE ZIM DOMAIN (JAZ) repressors through either 63 physical interaction or recruitment of the general co-repressor TOPLESS (TPL) or TPL-related 64 proteins (TPRs) (Chini et al., 2007; Thines et al., 2007; Yan et al., 2007). The adaptor NOVEL 65 INTERACTOR OF JAZ (NINJA) mediates interaction of JAZs with TPL or TRPs (Pauwels et 66 al., 2010). During activation, marked by accumulation of JA-Ile, JAZs form co-receptor 67 complexes with COI1. This interaction is facilitated by JA-Ile, which acts as a molecular glue 68 (Sheard et al., 2010). Formation of the co-receptor complexes triggers ubiquitylation and 69 proteasome-dependent degradation of the targeted JAZs, thereby releasing the transcription 70 factors to transcriptionally induce or repress their downstream target genes. Biochemical 71 studies suggest that JAZ-dependent ...

The plant epidermis serves many essential functions, including interactions with the environment, protection, mechanical strength, and regulation of tissue and organ growth. To achieve these functions, specialized epidermal cells develop into particular shapes. These include the intriguing interdigitated jigsaw puzzle shape of cotyledon and leaf pavement cells seen in many species, the precise functions of which remain rather obscure. Although pavement cell shape regulation is complex and still a long way from being fully understood, the roles of the cell wall, mechanical stresses, cytoskeleton, cytoskeletal regulatory proteins, and phytohormones are becoming clearer. Here, we provide a review of this current knowledge of pavement cell morphogenesis, generated from a wealth of experimental evidence and assisted by computational modeling approaches. We also discuss the evolution and potential functions of pavement cell interdigitation. Throughout the review, we highlight some of the thought-provoking controversies and creative theories surrounding the formation of the curious puzzle shape of these cells.

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