The NAC family is considered one of the largest plant-specific transcription factors families.The functions in diverse and vital physiological processes related to growth and development,and are involved in the response to abiotic and biotic stress.SNAC4-9 are members of the NAC family genes in tomato and are involved in the ripening process.In our study,SNAC4-9 expression and changes of physiological parameters were analyzed in tomato under various abiotic conditions and hormone treatments.The results demonstrated that all six selected genes were induced by these stresses with differential induction levels.SNAC4-9 expression was altered in response to hormone treatments(ABA,SA,and MeJA).indicating that SNAC4-9 gene expression was likely related to the ABA,SA and MeJA signaling pathways.This study combines molecular biology and physiology to provide valuable information for further exploring the functional roles of NAC genes in response to environmental stresses.Based on SNACs amino acid sequence and searching through the Arabidopsis NAC transcription factor database provided by PlantTFDB,we found that SNAC4 was best matched with ANAC056 and SNAC9 was best matched with ATNAP.The TRV-SNAC VIGS fruit significantly developed green color phenotypes delaying fruit ripening.Dissection of silenced areas for QPCR analysis identified that silencing of SNAC genes repressed LeACS2,LeEIL and NR expressions,and induced LeERF and LeRIN expressions.All the gene expressions were inhibited with SNAC9 silencing.EMSA experiments showed that SNAC 4/9 may be associated with the regulation of ACO and ACS.The results indicated that a mechanism link existed between SNAC and biosynthesis,perception and signal transduction of ethylene in fruit ripening in tomato.