Induced secretion system mutation alters rhizosphere bacterial composition in Sorghum bicolor (L.) Moench

Authors: BALASUBRAMANIAN, VIMAL - Texas Tech University; DAMPANABONIA, LAVANYA - Texas Tech University; YUAN, NING - Texas Tech University; COBOS, CHRIS - Texas Tech University; Xin, Zhanguo; MENDU, VENUGOPAL - Texas Tech University

Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2021
Publication Date: 1/18/2021
Citation: Balasubramanian, V.K., Dampanabonia, L., Yuan, N., Cobos, C., Xin, Z., Mendu, V. 2021. Induced secretion system mutation alters rhizosphere bacterial composition in Sorghum bicolor (L.) Moench. Planta. https://doi.org/10.1007/s00425-021-03569-5.
DOI: https://doi.org/10.1007/s00425-021-03569-5

Interpretive Summary: Previous studies on a wide range of plant species have shown that microbial communities in the root zone may play a role in plant health, stress tolerance, and yield. The presence, composition, and health of the microbial communities is regulated by soil type, environmental conditions, and in many instances the plant itself through chemicals exuded by the root that promote microbial growth. Sorghum is a major crop in rainfed production systems across the US Great Plains and is known to have positive interactions with specific types of bacteria during periods of drought stress. This interaction between sorghum and the bacteria make the plants more resilient to drought. This interaction is based on a chemical exudate from the plant that recruits bacteria to the root zone. Although data exists on the specific chemical signal, little is known about plants regulate microbial populations in the root zone and whether this signaling mechanism can be manipulated to enhance sorghum stress tolerance. In collaboration with scientists from Texas Tech University, ARS scientist at Lubbock, Texas isolated a red root (RR) sorghum mutant that has an enhanced level of chemical secretion from roots. Specifically, RR plants secrete high levels of secondary chemicals called phenolics that attract a specific class of bacteria to the root zone. This study describes the mutation responsible for the RR sorghum and the effect of increased phenolic secretion on the soil microbial community. The RR mutant and an increased understanding of the root-microbe interactions provides novel tool to study these interactions and potentially improve sorghum drought tolerance and yield in rainfed and water-limited systems.

Technical Abstract: Favorable plant-microbe interactions in rhizosphere have been known to positively impact plant growth and stress tolerance. Sorghum bicolor, a staple biomass and food crop, is known to select Gram-positive bacteria (actinobacteria) in its rhizosphere under drought to enhance stress tolerance. However, the genetic/biochemical mechanism underlying the selective enrichment of specific microbial phyla in sorghum is not well understood, due to the lack of mutants that show altered root exudation profile. Using a subset of sorghum EMS lines, we have isolated a sorghum mutant, designated as RedRoot (RR), in which a single dominant genetic mutation was found to increase root specific accumulation of phenolic compounds. The microbiome diversity analysis showed that RR mutant selectively enriched Actinobacteria, Alpha-proteobacteria in its rhizosphere under well-watered condition. Under water stressed condition, RR mutant retained a higher bacterial interaction in the rhizosphere than the wild type plant. The nature of RR gene and its molecular mechanism through which the mutant plant selectively enriches microbial populations in the rhizosphere may be useful in designing strategies to improve sorghum productivity and stress tolerance.