ENO regulates tomato fruit size through the floral meristem development network

A dramatic evolution of fruit size has accompanied the domestication and improvement of fruit-bearing crop species. In tomato (Solanum lycopersicum), naturally occurring cis-regulatory mutations in the genes of the CLAVATA-WUSCHEL signaling pathway have led to a significant increase in fruit size generating enlarged meristems that lead to flowers with extra organs and bigger fruits. In this work, by combining mapping-by-sequencing and CRISPR/Cas9 genome editing methods, we isolated EXCESSIVE NUMBER OF FLORAL ORGANS (ENO), an AP2/ERF transcription factor which regulates floral meristem activity. Thus, the ENO gene mutation gives rise to plants that yield larger multilocular fruits due to an increased size of the floral meristem. Genetic analyses indicate that eno exhibits synergistic effects with mutations at the LOCULE NUMBER (encoding SlWUS) and FASCIATED (encoding SlCLV3) loci, two central players in the evolution of fruit size in the domestication of cultivated tomatoes. Our findings reveal that an eno mutation causes a substantial expansion of SlWUS expression domains in a flower-specific manner. In vitro binding results show that ENO is able to interact with the GGC-box cis-regulatory element within the SlWUS promoter region, suggesting that ENO directly regulates SlWUS expression domains to maintain floral stem-cell homeostasis. Furthermore, the study of natural allelic variation of the ENO locus proved that a cis-regulatory mutation in the promoter of ENO had been targeted by positive selection during the domestication process, setting up the background for significant increases in fruit locule number and fruit size in modern tomatoes

Decoding gene expression signatures underlying vegetative to inflorescence meristem transition in the common bean

The tropical common bean (Phaseolus vulgaris L.) is an obligatory short-day plant that requires relaxation of the photoperiod to induce flowering. Similar to other crops, photoperiod-induced floral initiation depends on the differentiation and maintenance of meristems. In this study, the global changes in transcript expression profiles were analyzed in two meristematic tissues corresponding to the vegetative and inflorescence meristems of two genotypes with different sensitivities to photoperiods. A total of 3396 differentially expressed genes (DEGs) were identified, and 1271 and 1533 were found to be up-regulated and down-regulated, respectively, whereas 592 genes showed discordant expression patterns between both genotypes. Arabidopsis homologues of DEGs were identified, and most of them were not previously involved in Arabidopsis floral transition, suggesting an evolutionary divergence of the transcriptional regulatory networks of the flowering process of both species. However, some genes belonging to the photoperiod and flower development pathways with evolutionarily conserved transcriptional profiles have been found. In addition, the flower meristem identity genes APETALA1 and LEAFY, as well as CONSTANS-LIKE 5, were identified as markers to distinguish between the vegetative and reproductive stages. Our data also indicated that the down-regulation of the photoperiodic genes seems to be directly associated with promoting floral transition under inductive short-day lengths. These findings provide valuable insight into the molecular factors that underlie meristematic development and contribute to understanding the photoperiod adaptation in the common bean

The Salt Sensitivity Induced by Disruption of Cell Wall-Associated Kinase 1 (SlWAK1) Tomato Gene Is Linked to Altered Osmotic and Metabolic Homeostasis

omato cell wall-associated kinase 1 (SlWAK1) has only been studied in biotic stress response and hence its function in abiotic stress remains unknown. In a screening under salinity of an insertional mutant collection of tomato (Solanum lycopersicum L.), a mutant exhibiting lower degree of leaf chlorosis than wild type (WT) together with reduced leaf Na+ accumulation was selected. Genetic analysis of the mutation revealed that a single T-DNA insertion in the SlWAK1 gene was responsible of the mutant phenotype. Slwak1 null mutant reduced its shoot growth compared with WT, despite its improved Na+ homeostasis. SlWAK1 disruption affected osmotic homeostasis, as leaf water content was lower in mutant than in WT under salt stress. In addition, Slwak1 altered the source-sink balance under salinity, by increasing sucrose content in roots. Finally, a significant fruit yield reduction was found in Slwak1 vs. WT under long-term salt stress, mainly due to lower fruit weight. Our results show that disruption of SlWAK1 induces a higher sucrose transport from source leaf to sink root, negatively affecting fruit, the main sink at adult stage