The Mechanism Of Root Growth Regulated By SDM1 In Response To Sugar In Arabidopsis

According to previous study,nearly most of the plants live with a sessile growth.As for the plant,root plays an important role during the adaptation to the environment.Well developed root system can ensure that plants absorb more water and mineral nutrients from the soil and are more conducive to adapt plant to the environment.Studies on the growth of plant roots have been reported extensively which are mainly studied with model plant Arabidopsis thaliana as experimental material.There is a close relationship between the primary root growth and the photosynthesis of the plants,sucrose produced via photosynthesis is transported through the phloem to the root,thus the growth of the primary root is promoted.In addition,the glucose signal is sensed by the plant through TOR kinase,activates the apical meristem and promotes the growth of the primary root.There are also many studies about the relation between sugars and phytohormones that sugar acts as a signaling molecule that regulates the synthesis and transport of phytohormones,thereby regulating plant growth and development.In the experiment,a sugar-dependent mutant was found named sdm1,the sdm1 mutant exerted a low ability to grow normally under the condition of sugar-free medium due to the mutation of SDM1,which mainly presented that the growth is stagnation,the cotyledons is thinner and transparent and the function defective in the the conversion of heterotrophic to autotrophic.Interestingly,the growth and development of the sdm1 mutant was rescued in the presence of sucrose or glucose,the conversion of heterotrophic to autotrophic was done,however the fructose was not able to rescue the phenotype that the growth of the mutant is stagnation under the condition of sugar-free medium.Through the experiment of local conducted with sugar,it was found that only when the cotyledon was added with sugar,can the growth of the primary root be rescued.Meanwhile,through the detection of the content and activity of auxin in primary root with DR5::GUS tissue localization and Non-invasive Micro-test Technique,it was discovered that in the primary root of wild type and the sdm1 mutant,the level and activity of the auxin were all high in the presence of sugar,and when conducted with sugar-free medium,the auxin level and activity of the sdm1 mutant were significantly lower than the wild type.The expression of auxin efflux transporter PINs and auxin synthesis related genes YUCs in primary root was also analyzed.It was found that sugar could induce the expressionof these genes,and mutations of SDM1 resulted in a significant reduction in the expression of PINs and YUCs on sugar-free medium.It can be shown that the genes related to auxin synthesis and transport are all induced by sugar.The mutations of SDM1 could lead to a photomorphogenesis defect during the early stage of Arabidopsis thaliana seedlings.The cotyledons were the main parts of auxin synthesis during the development of plant seedlings.The decrease of photosynthetic sugar content would lead to the decrease of auxin synthesis in cotyledons,thus resulting in the reduction of sugar and auxin transported to the root apex and leading to an unnormal growth of sdm1 mutant primary root under the condition of sugar-free medium.The experiment shows that only the PINs and YUCs are all expressed at a normal can the primary root of plant grow normally.The important regulatory function of SDM1 in the growth and development of Arabidopsis thaliana provides a revelation for the study of the homologous genes in Gossypium hirsutum.Through the homology analysis of SDM1 among different species,SDM1 was found to be a common protein existing in many species and highly homologous to each other,and the homology of SDM1 in Arabidopsis thaliana and cotton was 74.8%,and the phenotype of Arabidopsis sdm1 transformed with Gh SDM1 was restored that mutant plants can not only restore the defect of sdm1 mutant hypocotyls phototropic curvant,but also can restore the phenotype of the primary root growth on the sugar-free medium,indicating that AtSDM1 and GhSDM1 are highly conservatism in function.The result further illustrates the important role of SDM1 in Arabidopsis thaliana growth and development.