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Article|19 Feb 2022|OPEN
Diversity and conservation of plant small secreted proteins associated with arbuscular mycorrhizal symbiosis
Xiao-Li Hu1,2 ,† , Jin Zhang3 ,† , Rakesh Kaundal4 , Raghav Kataria4 , Jesse L. Labbé2 , Julie C. Mitchell2 , Timothy J. Tschaplinski2,5 and Gerald A. Tuskan2,5 , Zong-Ming (Max) Cheng1,6 , , Xiaohan Yang,1,2,5 ,
1Department of Plant Sciences, University of Tennessee, Knoxville, TN 37996, USA
2Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
3State Key Laboratory of Subtropical Silviculture, Zhejiang A&F University, Hangzhou, Zhejiang 311300, China
4Department of Plants, Soils and Climate, Utah State University, Logan, UT 84322, USA
5The Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
6College of Horticulture, Nanjing Agricultural University, Nanjing, Jiangsu 210095 China
*Corresponding author. E-mail:,
Both authors contributed equally to the study.

Horticulture Research 9,
Article number: uhac043 (2022)
Views: 23

Received: 19 Aug 2021
Accepted: 18 Jan 2022
Published online: 19 Feb 2022


Arbuscular mycorrhizal symbiosis (AMS) is widespread mutualistic association between plants and fungi, which plays an essential role in nutrient exchange, enhancement in plant stress resistance, development of host, and ecosystem sustainability. Previous studies have shown that plant small secreted proteins (SSPs) are involved in beneficial symbiotic interactions. However, the role of SSPs in the evolution of AMS has not been well studied yet. In this study, we performed computational analysis of SSPs in 60 plant species and identified three AMS-specific ortholog groups containing SSPs only from at least 30% of the AMS species in this study and three AMS-preferential ortholog groups containing SSPs from both AMS and non-AMS species, with AMS species containing significantly more SSPs than non-AMS species. We found that independent lineages of monocot and eudicot plants contained genes in the AMS-specific ortholog groups and had significant expansion in the AMS-preferential ortholog groups. Also, two AMS-preferential ortholog groups showed convergent changes, between monocot and eudicot species, in gene expression in response to arbuscular mycorrhizal fungus Rhizophagus irregularis. Furthermore, conserved cis-elements were identified in the promoter regions of the genes showing convergent gene expression. We found that the SSPs, and their closely related homologs, in each of three AMS-preferential ortholog groups, had some local variations in the protein structural alignment. We also identified genes co-expressed with the Populus trichocarpa SSP genes in the AMS-preferential ortholog groups. This first plant kingdom-wide analysis on SSP provides insights on plant-AMS convergent evolution with specific SSP gene expression and local diversification of protein structures.