The Mechanism Of Regulating Flowering Time By SELF PRUNING 5G(SP5G) In Tomato

Tomato?Solanum lycopersicum?is a popular vegetable,which is cultivated worldwide.Cultivated tomatoes were derived from their wild relatives,Solanum pimpinellifolium,by domestication and improvement.Most of the cultivars are day-neutral plants.In contrast,wild species originated from the Andean region in South America are short-day?SD?plants and flower late during long-day?LD?conditions.Flowering time is an important agronomic trait that determines the growth period and environmental adaption of crops.However,genes controlling flowering time in tomato,especially responding to photoperiod,are less reported.The molecular mechanisms of photoperiodic response in tomato remain unknown.In this study,we investigated the flowering time of the wild species,cherry and big-fruit cultivars and found that the wild species are sensitive to photoperiod,whereas the cultivated tomatoes show weak day-length sensitivity.To further explore the genetic basis of the difference of photoperiodic sensitivity between these two tomato species,we generated a recombination inbred lines?RILs?population by crossing S.lycopersicum cv.Moneymaker,a big-fruit cultivar,with S.lycopersicum var.cerasiforme?LA1310?,a cherry tomato accession,which display different sensitivity to day length,respectively.A major locus,Q-fo1₀1,were identified by Genome-wide association study?GWAS?in the RILs.We mapped the gene by generating near-isogenic lines?NILs?and found that this gene located within nearly 50-kb region at the end of chromosome 5,in which SELF PRUNING 5G?SP5G??Solyc05g053850?,a homologue of Arabidopsis FT,was identified.When SP5 G was knocked out in tomato,the mutants showed insensitivity to LD condition.Thus SP5 G contributed to the photoperiod sensitivity in tomatoes and was positively seleted during domestication.We tested the expression patterns of SP5 G under LD or SD and found that the transcripts of SP5 G are dynamically changed during LD condition,while extremely low in SD.The difference of SP5 G expression patterns between NILs may cause the different photoperiod sensitivety.We further proved that the 3' untranslated region?UTR?of SP5 G acts as an enhancer to promote the transcripts of SP5 G by dual-luciferase reporter assay.A 52-bp sequence within SP5 G 3'UTR is important for the enhancer activity.Absent of the 52-bp sequence resulted in the decrease of SP5 G transcripts in the cultivated allele.Moreover,RNA polymerase II?Pol II?was significantly enriched near the 52-bp sequence at SP5 G 3'UTR and helped it to interact with the SP5 G promoter region.The absence of the 52-bp sequence in the 3'UTR of SP5 G represses the loop formation between promoter and the 3'UTR.In conclusion,we proved that the 3' untranslated region?UTR?of SP5 G acted as an enhancer which could interact with SP5 G promoter by forming a loop to regulate SP5 G expression in tomato.The absence of a 52-bp sequence within 3' UTR caused a weakened promoter-enhancer interaction and repressed the transcription level of SP5 G,which resulted in the weak photoperiod response in cultivars.