Roles of SlETR7,a newly discovered ethylene receptor,in tomato plant and fruit development

Ethylene regulates many aspects of plant growth and development.It is perceived by a family of ethylene receptors(ETRs)that have been well described.However,a full understanding of ETR function is complicated by functional redundancy between the receptor isoforms.Here,we characterize a new ETR,SlETR7,that was revealed by tomato genome sequencing.SlETR7 expression in tomato fruit pericarp increases when the fruit ripens and its expression is synchronized with the expression of SlETR1,SlETR2,and SlETR5 which occurs later in the ripening phase than the increase observed for SlETR3,SlETR4,and SlETR6.We uncovered an error in the SlETR7 sequence as documented in the ITAG 3 versions of the tomato genome which has now been corrected in ITAG 4,and we showed that it belongs to sub-family II.We also showed that SlETR7 specifically binds ethylene.Overexpression(OE)of SlETR7 resulted in earlier flowering,shorter plants,and smaller fruit than wild type.Knock-out(KO)mutants of SlETR7 produced more ethylene at breaker(Br)and Br+2 days stages compared to wild type(WT),but there were no other obvious changes in the plant and fruit in these mutant lines.We observed that expression of the other SlETRs is upregulated in fruit of SlETR7 KO mutants,which may explain the absence of obvious ripening phenotypes.Globally,these results show that SlETR7 is a functional ethylene receptor.More work is needed to better understand its specific roles related to the six other tomato ETRs.

The SlTPL3–SlWUS module regulates multi-locule formation in tomato by modulating auxin and gibberellin levels in the shoot apical meristem

Malformed fruits depreciate a plant’s market value.In tomato(Solanum lycopersicum),fruit malformation is associated with the multi-locule trait,which involves genes regulating shoot apical meristem(SAM)development.The expression pattern of TOPLESS3(SITPL3)throughout SAM development prompted us to investigate its functional significance via RNA interference(RNAi)and clustered regularly interspaced short palindromic repeats/CRISPR-associated nuclease 9(Cas9)-mediated gene editing.Lower SITPL3 transcript levels resulted in larger fruits with more locules and larger SAMs at the 5 d after germination(DAG5)stage.Differentially expressed genes in the SAM of wild-type(WT)and SITPL3-RNAi plants,identified by transcriptome deep sequencing(RNA-seq),were enriched in the gibberellin(GA)biosynthesis and plant hormone signaling pathways.Moreover,exogenous auxin and paclobutrazol treatments rescued the multi-locule phenotype,indicating that SITPL3 affects SAM size by mediating auxin and GA levels in the SAM.Furthermore,SITPL3 interacted with WUSCHEL(SIWUS),which plays an important role in SAM size maintenance.We conducted RNA-seq and DNA affinity purification followed by sequencing(DAP-seq)analyses to identify the genes regulated by SITPL3 and SIWUS in the SAM and to determine how they regulate SAM size.We detected24 overlapping genes regulated by SITPL3 and SIWUS and harboring an SIWUS-binding motif in their promoters.Furthermore,functional annotation revealed a notable enrichment for functions in auxin transport,auxin signal transduction,and GA biosynthesis.Dual-luciferase assays also revealed that SITPL3 enhances SIWUS-mediated regulation(repression and activation)of SIPIN3 and SIGA2 ox4 transcription,indicating that the SITPL3-SIWUS module regulates SAM size by mediating auxin distribution and GA levels,and perturbations of this module result in enlarged SAM.These results provide novel insights into the molecular mechanism of SAM maintenance and locule formation in tomato and highlight the SITPL3-SIWUS module as a key regulator.