Pathogenesis-related 10 (PR-10) is a group of small intracellular proteins that is one of 17 subclasses of pathogenesis-related proteins in plants. The PR-10 proteins have been studied extensively and are well-recognized for their contribution to host defense against phytopathogens in several plant species. Interestingly, the accumulation of PR-10 proteins in the rubber tree, one of the most economically important crops worldwide, after being infected by pathogenic organisms has only recently been reported. In this study, the homologous proteins of the PR-10 family were systemically identified from the recently available rubber tree genomes in the NCBI database. The sequence compositions, structural characteristics, protein physical properties, and phylogenetic relationships of identified PR-10 proteins in rubber trees support their classification into subgroups, which mainly consist of Pru ar 1-like major allergens and major latex-like (MLP) proteins. The rubber tree PR10-encoding genes were majorly clustered on chromosome 15. The potential roles of rubber tree PR-10 proteins are discussed based on previous reports. The homologous proteins in the PR-10 family were identified in the recent genomes of rubber trees and were shown to be crucial in host responses to biotic challenges. The genome-wide identification conducted here will accelerate the future study of rubber tree PR-10 proteins. A better understanding of these defense-related proteins may contribute to alternative ways of developing rubber tree clones with desirable traits in the future.

Class 10 of pathogenesis-related proteins (PR-10) is a class of PR proteins localized in the cytoplasm ( Agarwal and Agarwal 2014). Members of the PR-10 protein family are part of the major latex-like protein family and can be induced by the infection with various pathogens ( Fujita and Inui 2021). Recently, we identified a novel PR-10 protein from rubber tree (Hevea brasiliensis), previously known as protein LOC110648447, which accumulates in leaves in response to root infection by white root rot fungi, Rigidoporus microporus ( Longsaward et al. 2023). Sequence similarity and predicted 3D structure indicate that HbPR10 is a member of the Bet v 1/PR-10 protein family.

We studied the biochemical properties of three splicing isoforms of PR-10 from rubber tree ( Hevea brasiliensis ) and found that purified recombinant Hb PR10 can cause RNA degradation in vitro , a well-known activity described for many PR-10 proteins. This ribonuclease activity was observed for all three Hb PR10 splicing isoforms and is abolished by boiling. However, inclusion of a negative control proteins revealed that ribonuclease activity rather originates from RNases that are copurified from E. coli , which are overlooked by traditionally used controls such as heat inactivation, RNase inhibitors and negative control proteins obtained with different procedures. The crucial control proteins are missing for at least nine reports on ribonuclease activity in PR-10 proteins published by different laboratories worldwide, indicating that proper controls are frequently overlooked in ribonuclease assays. The raised cautionary note applies to several PR-10 proteins with proclaimed ribonuclease activities and call for the use of different assays and mutant PR-10 proteins as control.