Auxin response factor 6A regulates photosynthesis,sugar accumulation,and fruit development in tomato

Auxin response factors(ARFs)are involved in auxin-mediated transcriptional regulation in plants.In this study,we performed functional characterization of SlARF6A in tomato.SlARF6A is located in the nucleus and exhibits transcriptional activator activity.Overexpression of SlARF6A increased chlorophyll contents in the fruits and leaves of tomato plants,whereas downregulation of SlARF6A decreased chlorophyll contents compared with those of wild-type(WT)plants.Analysis of chloroplasts using transmission electron microscopy indicated increased sizes of chloroplasts in SlARF6A-overexpressing plants and decreased numbers of chloroplasts in SlARF6A-downregulated plants.Overexpression of SlARF6A increased the photosynthesis rate and accumulation of starch and soluble sugars,whereas knockdown of SlARF6A resulted in opposite phenotypes in tomato leaves and fruits.RNA-sequence analysis showed that regulation of SlARF6A expression altered the expression of genes involved in chlorophyll metabolism,photosynthesis and sugar metabolism.SlARF6A directly bound to the promoters of SlGLK1,CAB,and RbcS genes and positively regulated the expression of these genes.Overexpression of SlARF6A also inhibited fruit ripening and ethylene production,whereas downregulation of SlARF6A increased fruit ripening and ethylene production.SlARF6A directly bound to the SAMS1 promoter and negatively regulated SAMS1 expression.Taken together,these results expand our understanding of ARFs with regard to photosynthesis,sugar accumulation and fruit development and provide a potential target for genetic engineering to improve fruit nutrition in horticulture crops.

CRISPR/Cas9-mediated gene-editing technology in fruit quality improvement

Fruits are an essential part of a healthy,balanced diet and it is particularly important for fibre,essential vitamins,and trace elements.Improvement in the quality of fruit and elongation of shelf life are crucial goals for researchers.However,traditional techniques have some drawbacks,such as long period,low efficiency,and difficulty in the modification of target genes,which limit the progress of the study.Recently,the clustered regularly interspaced short palindromic repeats(CRISPR)/Cas9 technique was developed and has become the most popular gene-editing technology with high efficiency,simplicity,and low cost.CRISPR/Cas9 technique is widely accepted to analyse gene function and complete genetic modification.This review introduces the latest progress of CRISPR/Cas9 technology in fruit quality improvement.For example,CRISPR/Cas9-mediated targeted mutagenesis of RIPENING INHIBITOR gene(RIN),Lycopene desaturase(PDS),Pectate lyases(PL),SlMYB12,and CLAVATA3(CLV3)can affect fruit ripening,fruit bioactive compounds,fruit texture,fruit colouration,and fruit size.CRISPR/Cas9-mediated mutagenesis has become an efficient method to modify target genes and improve fruit quality.