| Phytohormones and their interaction play critical roles in potato tuberization,maintaining dormancy,tuber sprouting and plant architecture.The stimulatory role of jasmonic acid(JA)in tuber development is well established because of its significant effect on tuber initiation and tuber bulking.In addition,the contribution of jasmonic acid under heat stress and drought stress is documented in different crops.However,the dynamics and potential function of JA signaling in potato tuberization and plant architecture as well as responses under high temperatures and drought stress,still remains largely unknown.In this thesis,the morphological,physiological and molecular regulatory networks of JA signaling during potato tuberization as well as responses under high temperatures and drought stress have been illustrated by using St JAZ1-like overexpression which is a JAZ1 subtype,a suppressor of JA signaling.Here,the function and regulatory mechanism of St JAZ1-like mediated JA signaling during potato tuberization,tuber sprouting and plant architecture have been demonstrated which provided theoretical bases and technical support for the breeding of potato to increase yield potentiality.In addition,the present study provided important clues to the response of JA signaling in potato plants under warm temperatures and drought stress.The important research results are as follows.1.Modulation of JA signaling reveals by St JAZ1-like ox mediated potato tuberization:Using 35S:St JAZ1-like-GUS as a reporter,we showed that JA signaling was attenuated from the bud end to the stem end shortly after tuber initiation.Overexpression of St JAZ1-like suppressed tuber initiation by restricting the competence for tuber formation in stolon tips,as demonstrated by grafting an un-transformed potato cultivar to the stock of St JAZ1-like-overexpressing transgenic potato plants(St JAZ1-like ox).As a result,the number of tubers per plant decreases,which ultimately reduces potato tuber yield.But the overexpression of St JAZ1-like has no impact on photosynthates or does not modulate the diurnal oscillation pattern of key tuberization signaling genes St SP6A,St CDF1,St BEL5 and St COL1 under short day condition.In addition,transcriptional profile analysis revealed that St JAZ1-like modulates the expression of genes associated with transcriptional regulators,cell cycle,cytoskeleton,and phytohormones.Therefore,JA signaling regulates potato tuberization through restricting the competence of tuberization,modulating cell cycle and cytoskeleton related genes,and networking with other phytohormones,whereas it has no influence on photosynthates and key tuberization signaling genes.Furthermore,St JAZ1-like is destabilized upon treatment with methyl jasmonate(Me JA)and abscisic acid(ABA),and the attenuated tuberization phenotype in St JAZ1-like ox plants can be entirely and partially rescued by Me JA and ABA treatment respectively.Moreover,from gene expression analysis,it was found that the expression of Allene Oxide Synthese(AOS),a key JA synthesis regulating gene,was higher in ABA treatmented wild type(E109)plants than untreated wild type(E109).Thus,JA and ABA may work synergistically during tuberization.2.Effects of St JAZ1-like ox in potato tuber sprouting and plant architecture:Overexpression of St JAZ1-like modulates tuber sprout apical dormancy and forms multiple sprouts on the same tuber at a time.As a result,after planting,a greater number of shoots emerge from a single tuber in contrast to wild type(WT),ultimately which influences the number and the size distribution of tubers.However,it has no influence on potato tuber dormancy breaking time.In addition,St JAZ1-like ox alters potato plant architecture by converting the stolon into branches instead of forming tubers along with reducing plant height,stem diameter,leaf size and root number.After planting the sprouted tuber,transgenic plants and WT produced almost the same number of tubers when all shoots were allowed to grow but the individual tuber weight(g)was significantly lower than that of the WT.The small size tubers are preferable for seed tuber production but during storage transgenic tubers rapidly shrank compared to WT tubers due to rapid loss of water.Thus,the JA signaling plays a role in regulating potato tuber quality during storage.Altogether,these results uncovered that St JAZ1-like-mediated JA signaling plays an essential role in potato tuber storage quality,breaking apical dominance,sprout number and strengthening potato plant architecture.3.St JAZ1-like mediated JA signaling response under warm temperature:Under the high temperature(35~oC),St JAZ1-like protein showed stability and under the warm temperatures(light/dark:26~oC/23~oC)St JAZ1-like ox transgenic lines exhibited reduced tuberization phenotypes compared to WT,which could be partially rescued by accompanying Me JA treatment both in vitro and in vivo conditions.Hence,the JA signaling may respond under heat stress and could ameliorate tuberization phenotypes.4.St JAZ1-like overexpressing plants were sensitive to drought stress:Under drought stres St JAZ1-like overexpressing transgenic plants exhibited susceptibility compared to WT plants.After the critical observation of the in vitro grown plant phenotypes,the in vivo grown plant phenotypes from mother tuber,and the grafted plant phenotypes,it was identified that the transgenic plants exhibited drought stress sensitivity due to a smaller number of adventitious roots.It was found Me JA could be able to increase the number of adventitious roots in potato overexpressing St JAZ1-like transgenic plants in a concentration dependent manner.Thus,the JA signaling may stimulate potato plant drought tolerance by modulating the root system.Taken together,St JAZ1-like overexpression mediated JA signaling facilitates the understanding of the role of JA in potato tuberization,tuber sprouting and plant architecture.Moreover,there is a prospect of JA contribution in increasing tuber yield of potato under adverse environments such as warm temperatures and water scarcity conditions. |
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