Functional Analysis Of Tomato NAC TFs SNAC4?9 In Response To Abiotic Stresses

Plants are exposed to kinds of environmental stresses such as drought, high salinity, heat and cold in the process of growth and development, which could adversely affect the growth and productivity of plants. Transcription factors that serves as members of signaling network, plays an important role in plant resistance to abiotic stresses. NAC family is a plant specific transcriptional factor family found in last decades of years, which is involved extensively in plant growth and stress resistance.In the current study, expressions of SNAC4~9 were analyzed in tomato(Solanum lycopersicum L., cv Ailsa Craig) seedlings under short-time drought, salt, heat, hormone treatments and long-time drought, salt treatments and hormone treatments. We also did physiological analysis of the seedlings under abiotic stresses and hormone treatments to provide more information for stress resistant plants. RNAi expression vectors of SNAC4~9 of were constructed to provide materials for our future studies. The results are as follows:1. Expression of SNAC4, SNAC8 and SNAC9 were induced by almost all abiotic stresses except SNAC4, SNAC9 in short-term drought treatment and SNAC9 in cold stress, suggesting that SNAC4, SNAC8 and SNAC9 are associated with various stresses. The SNAC5 transcript accumulated to higher level in short-term salt, heat and cold treatments, whereas reduced in long-term drought and salt treatments. Thus SNAC5 probably plays a major role in heat and cold resistance and functions differently in short-term and long-term drought and salt stresses. Expression of SNAC6 was low in seedling, but it was still induced by heat stress(over 24 h) and long-term salt stress, meanwhile, reduced in short-term cold treatment. Thus it may likely function in response to these stresses. SNAC7 was induced in salt and heat treatments and reduced in long-term drought stress, indicating its positive role in salt and heat resistance and negative role in drought stress in long term.2. In tomato plants sprayed with ABA, SA or MeJA, SNAC4, SNAC5, SNAC7, SNAC9 transcript levels were up-regulated and peaked at 8 h, 8 h, 4 h and 12 h of treatment separately and declined thereafter, whereas the expression level of SNAC6 was decreased. SNAC8 was induced in ABA, SA(over 48 h) and MeJA(over 2 h) treatments. Thus SNAC4~9 might interact with environmental and endogenous stimuli and probably function when plants response to drought, salt, cold and heat stresses through ABA, SA and MeJA signaling pathways as transcriptional activators.3. Proline contents and APX, CAT, POD, SOD activities were significantly higher in hormone and abiotic stress treatments than in the control. MDA was higher in various abiotic stresses than in the control, and correlation analysis also showed that MDA was correlated with at least two enzymes(P<0.05). The lower MDA content in seedlings under ABA, SA and MeJA treatments and higher MDA content in seedlings under abiotic stress treatments suggests SNAC4~9 might increase stress resistance ability of plant by increasing the activities of ROS-scavenging enzymes through ABA, SA and MeJA signaling pathways.