Effect of rhizospheric and endophytic bacteria on root development of Arabidopsis thaliana and auxin mutants.

Abstract

Plant root growth is one of the most important factor in determining the plant health and increased crop production. Factors like root length, root hairs and number of secondary roots are crucial for the intake and availability of unreachable nutrients in soil. Plant roots are inhabited by large number of microbes called root microbiome. Utilizing beneficial root microorganism to promote plant growth can have lasting effect on plants ability to resist unfavorable environmental stresses and achieve optimized growth. In this study known plant growth promoting rhizospheric and endophytic bacteria as well as newly isolated bacteria from tomato specie Solanum pimpinellifolium are tested on Arabidopsis thaliana, Gemini tomato plant and mutant pin2, wei8/wei2, tir1 and aux1-7 which are mutants defective in polar auxin transport and auxin signaling. The plant seedlings were grown on agar solidified 1/50 X Gamborg’s B5 nutrient medium and also on 1 X Murashige and Skoog nutrient medium. The bacterial culture was inoculated to vertical agar plates under two different conditions: sucrose supplemented nutrient medium and without sucrose medium. Roots of hydroponically growing Solanum pimpinellifolium tomato plants were utilized to isolate the root endophytes. 16S gene sequencing analysis revealed the identity of bacterial species. Three bacterial isolates recovered from the S.pimpinellifolium roots are Micrococcus yunnanensis, Cohnella spp. and Bacillus flexis. Newly isolated bacterial strains Micrococcus yunnanensis and Cohnella spp. were inoculated to the Gemini tomato plants in a pot experiment to check if they have any beneficial growth promoting traits. During the course of this project we were able to find that bacterial strain 9 and 15 (Pseudomonas spp. & Agrobacterium spp.) received from Gennao Roberto Abbamondi, Hasselt University, Belgium are able to stimulate root hair development in Col-0 and also in mutants pin2, wei8/wei2, tir1 and aux1-7. Among newly isolated strains M.yunnanensis is able to stimulate the primary root length to some extent, number of lateral roots and shoot weight in WT Col-0 in plants growing in 1 X MS medium supplemented with sucrose. M.yunnanensis is also shown to have some effect on shoot length and shoot weight of Gemini tomato plants. Pseudomonas fluorescence (WCS417) is able to stimulate primary root length, number of lateral roots and shoot fresh weight in Col-0, pin2 and also in aux1-7 mutant