The Predominance of Proteobacteria and Cyanobacteria in the Cycas dolichophylla Coralloid Roots Revealed by 16S rRNA Metabarcoding

Abstract: The endophytes of plants are receiving increased attention since they have important functions for improving plant growth and fitness, especially in more challenging environmental conditions. The adaptation of cycads, an ancient gymnosperm taxon, to arid and nutrient-limited habitats is thought to be dependent on their symbiosis with nitrogen-fixing Cyanobacteria. We investigated the endophytic community in seeds, taproots, and young and mature coralloid roots of Cycas dolichophylla using 16S rRNA metabarcoding. Geographically distinct populations were studied in China and Vietnam. Higher endophyte diversity was found in Vietnamese populations than in Chinese ones. A significant difference in the bacterial endophytic community was identified between populations of mature coralloid roots from Chinese and Vietnamese samples, with the predominance of Alpha-, Gamma-, and Beta-Proteobacteria in the Vietnamese samples. Moreover, five core endophytic families, Nostocaceae, Burkholderiaceae, Pseudomonadaceae, Enterobacteriaceae, and Rhizobiaceae were revealed among all the samples. This study offers a robust knowledge of cycad microbial ecology and lends guidelines to the investigation of the adaptation mechanism of cycads in arid and nutrient-poor environments.