Auxin plays a key role in lateral root formation, but the signaling pathway for this process is poorly understood. We show here thatNAC1, a new member of theNACfamily, is induced by auxin and mediates auxin signaling to promote lateral root development. NAC1 is a transcription activator consisting of an N-terminal conserved NAC-domain that binds to DNA and a C-terminal activation domain. This factor activates the expression of two downstream auxin-responsive genes,DBPandAIR3. Transgenic plants expressing sense or antisenseNAC1cDNA show an increase or reduction of lateral roots, respectively. Finally, TIR1-induced lateral root development is blocked by expression of antisenseNAC1cDNA, and NAC1 overexpression can restore lateral root formation in the auxin-response mutanttir1, indicating that NAC1 acts downstream of TIR1.

Summary: Formation of somatic embryos in plants is known to require high concentrations of auxin or 2,4‐dichlorophenoxyacetic acid (2,4‐D), which presumably acts to trigger a signalling cascade. However, very little is known about the molecular mechanism that mediates the vegetative‐to‐embryogenic transition. We have employed a genetic approach to dissect the signal transduction pathway during somatic embryogenesis. In a functional screen using a chemical‐inducible activation‐tagging system, we identified two alleles of Arabidopsis gene PGA6 whose induced overexpression caused high‐frequency somatic embryo formation in all tissues and organs tested, without any external plant hormones. Upon inducer withdrawal, all these somatic embryos were able to germinate directly, without any further treatment, and to develop into fertile adult plants. PGA6 was found to be identical to WUSCHEL (WUS), a homeodomain protein previously shown to be involved in specifying stem cell fate in shoot and floral meristems. Transgenic plants carrying an estradiol‐inducible XVE‐WUS transgene can phenocopy pga6‐1 and pga6‐2. Our results suggest that WUS/PGA6 also plays a key role during embryogenesis, presumably by promoting the vegetative‐to‐embryogenic transition and/or maintaining the identity of the embryonic stem cells.

Endives (Cichorium endivia L.) are popular vegetables, diversified into curly/frisée- and smooth/broad-leafed (escaroles) cultivar types (cultigroups), and consumed as fresh and bagged salads. They are rich in sesquiterpene lactones (STL) that exert proven function on bitter taste and human health. The assembly of a reference transcriptome of 77,022 unigenes and RNA-sequencing experiments were carried out to characterize the differences between endives and escaroles at the gene structural and expression levels. A set of 3177 SNPs distinguished smooth from curly cultivars, and an SNP-supported phylogenetic tree separated the cultigroups into two distinct clades, consistently with the botanical varieties of origin (crispum and latifolium, respectively). A pool of 699 genes maintained differential expression pattern (core-DEGs) in pairwise comparisons between curly vs smooth cultivars grown in the same environment. Accurate annotation allowed the identification of 26 genes in the sesquiterpenoid biosynthesis pathway, which included several germacrene A synthase, germacrene A oxidase and costunolide synthase members (GAS/GAO/COS module), required for the synthesis of costunolide, a key precursor of lactucopicrin- and lactucin-like sesquiterpene lactones. The core-DEGs contained a GAS gene (contig83192) that was positively correlated with STL levels and recurrently more expressed in curly than smooth endives, suggesting a cultigroup-specific behavior. The significant positive correlation of GAS/GAO/COS transcription and STL abundance (2.4-fold higher in frisée endives) suggested that sesquiterpenoid pathway control occurs at the transcriptional level. Based on correlation analyses, five transcription factors (MYB, MYB-related and WRKY) were inferred to act on contig83192/GAS and specific STL, suggesting the occurrence of two distinct routes in STL biosynthesis.

Flowering and seed set are essential for plant species to survive, hence plants need to adapt to highly variable environments to flower in the most favorable conditions. Endogenous cues such as plant age and hormones coordinate with the environmental cues like temperature and day length to determine optimal time for the transition from vegetative to reproductive growth. In a breeding context, controlling flowering time would help to speed up the production of new hybrids and produce high yield throughout the year. The flowering time genetic network is extensively studied in the plant model species Arabidopsis thaliana, however this knowledge is still limited in most crops. This article reviews evidence of conservation and divergence of flowering time regulation in A. thaliana with its related crop species in the Brassicaceae and with more distant vegetable crops within the Asteraceae family. Despite the overall conservation of most flowering time pathways in these families, many genes controlling this trait remain elusive, and the function of most Arabidopsis homologs in these crops are yet to be determined. However, the knowledge gathered so far in both model and crop species can be already exploited in vegetable crop breeding for flowering time control.

Leaves are specialized organs characterized by defined developmental destiny and determinate growth. The overexpression ofKnotted1-like homeobox genes in different species has been shown to alter leaf shape and development, but a definite role for this class of genes remains to be established. Transgenics that overexpress Knotted1-like genes present some traits that are characteristic of altered cytokinin physiology. Here we show that lettuce (Lactuca sativa) leaves that overexpressKNAT1, an Arabidopsis kn1-like gene, acquire characteristics of indeterminate growth typical of the shoot and that this cell fate change is associated with the accumulation of specific types of cytokinins. The possibility that the phenotypic effects of KNAT1 overexpression may arise primarily from the modulation of local ratios of different cytokinins is discussed.