The Correlations Between The K~+/Na~+ Transport In Different Root Zones And Salt Tolerance In Sweet Poato And The Effects Of IbPSS1 On The Salt Tolerance Of Sweet Potato

Soil salinization restricts the agriculture production worldwide and also impedes the crop yield in our country.To understand the physiological and molecular mechanisms of plant salt tolerance is important for the breeding of salt-resistant crop germplasms.Sweet potato(Ipomoea batatas(L).Lam)is an important food and industrial crop that ranks seventh in terms of worldwide staple food production.The growth and development of sweet potato is often affected by salt stress,which results in delayed development of storage roots and low yield.To explore the mechanisms of salt tolerance in sweet potato is meaningful for breeding salt tolerant sweet potato germplasms.Maintaining appropriate cellular Na~+/K~+homeostasis is one of important mechanism required for the salt tolerance in plants.The transport activities of Na~+and K~+in the roots is closely correlated to the salt tolerance in plants.However,whether the transport activities of Na~+and K~+in the roots under salinity conditions correlated to the salt tolerance in sweet potato is largely unknown.Meanwhile,the genes involved in the regulation of Na~+/K~+transport are still largely unknown.This dissertation measured the Na~+/K~+transport activities in different root regions of numerous sweet potato varieties using non-invasive micro-test technique(NMT)and confirmed the correlations between the Na~+/K~+transport activities and salt tolerance index measured in the laboratory or yield measured in the salinized field.In addition,the effects of Ib PSS1,which encodes a phosphatidylserine synthase in sweet potato,on the salt tolerance and Na~+transport activity in salinized roots were also investigated.The main results are listed as follows:(1)The salt-induced alterations of Na~+and K~+fluxes in the meristem,elongation and mature root zones were measured in 138 and 142 sweet potato cultivars(or breed lines)using NMT respectively.The results showed that the differences of salt-induced Na~+and K~+fluxes in different root regions among sweet potato varieties are substantial.(2)The salt tolerance index was measured in selected 72 varieties under long-term salt stress in the lab and divided into two groups(salt-sensitive and salt-tolerant)according to the salt tolerance index.Our results showed that the mean Na~+efflux in the elongation root zone of salt-tolerant group was significantly higher than that of salt-sensitive group.However,the K~+transport activity in the three root zones between the two groups did not show obvious difference.(3)Regression analysis showed that the amplitude of Na~+efflux in the elongation root zone exhibits significant positive correlation with the salt tolerance index.However,the amplitude of Na~+efflux measured in other root zones did not show this positive correlation with salt tolerance index.Furthermore,the K~+transport activity in the three root zones did not show any correlations with the salt tolerance index.(4)The ratio between the tuber roots yield of 72 varieties planted in the non-saline soil(Xuzhou)and saline soil(Yancheng)exhibited significant negative correlation with the salt tolerance index measured in the lab.Further regression analysis showed that this ratio also exhibits significant negative correlation with the amplitude of Na~+efflux measured in elongation root zone using NMT.These results indicate that the Na~+exclusion capability in the elongation zone of sweet potato adventitious roots is correlated to the tuber roots yield planted in the saline soil.(5)Transcriptomic data showed that the expression levels of genes related to the positive regulation of plasma membrane(PM)Na~+/H~+antiport activity in the roots(such as ANN1,ANN4,AHA1,CBL10,MPK6,FAD2,Rboh F,SOS3,CIPK23)of representative salt-tolerant variety(SD27)were significantly higher than that of SD9,which is a representative salt-sensitive variety with lower Na~+extrusion activity in the elongation root zone.However,the expression levels of genes related to the negative regulation of PM Na~+/H~+antiport activity(PKS5 and GI)in the roots of SD27 were significantly lower than that of SD9.(6)We further obtained the Ib PSS1-overexpressed transgenic sweet potato seedlings through Agrobacterium tumefaciens-mediated transformation method.Our results showed that the salt tolerance of Ib PSS1-OE seedlings was enhanced when compared with the wild type sweet potato seedlings.Interestingly,the enhanced salt-tolerance in these transgenic seedlings was correlated to the elevated Na~+extrusion capability in the elongation and mature root zones.Taken together,the results from this dissertation provided the solid evidence that the capability of Na~+extrusion in the elongation root zone of sweet potato is required for the salt tolerance and yield formation planted in the saline soil.We also discovered several genes related to the regulation of PM Na~+/H~+antiport activity in sweet potato using high-throughput sequencing.We further proved that Ib PSS1 improves the salt tolerance of sweet potato at the whole plant level through elevating PM Na~+/H~+antiport activity in the roots.Our results are important for breeding salt-tolerant sweet potato in the future through molecular breeding.