A kiwellin protein-like fold containing rust effector protein localizes to chloroplast and suppress cell death in plants

Abstract

The effector proteins expressed by plant pathogens are one of the essential components of the host-pathogen interaction. Despite being important, most of the effector proteins remain unexplored due to the lack of conserved features and huge diversity in their primary sequence. In the present study, extensive secretome analysis was performed in sixteen major plant fungal pathogens to find the conserved features in the candidate secretory effector proteins (CSEPs) using homology and ab initio modeling approaches. Interestingly, a variable number of plant kiwellin proteins fold like secretory proteins were found in all the major rust fungal pathogens. Many of them are predicted as potential effector proteins. For instance, 26 out of 35 Kiwellin like proteins identified in Puccinia striiformis race 104E 137A were predicted as potential effector proteins. In addition, a kiwellin predicted effector gene, Pst_13960, from the Indian Puccinia striiformis race Yr9 was characterized using overexpression, localization, and deletion studies in Nicotiana benthamiana. The Pst_13960 suppressed the BAX-induced cell death and localized in the chloroplast. Furthermore, the expression of the kiwellin matching region (Pst_13960_kiwi) alone suppressed the BAX-induced cell death in N. benthamiana despite the change of location to the cytoplasm and nucleus, suggesting the novel function of the kiwellin fold in rust fungi. Further analysis of these proteins predicted these candidates to contain N-terminal Intrinsically disordered regions (IDRs) putatively associated with chloroplast translocation as deletion of region abolished the chloroplast localization of Pstr_13960. Overall, the current study reports the presence of kiwellin like proteins in rust fungi that act as a novel effector in plants.

Evolutionary reconstruction, nomenclature and functional meta-analysis of the Kiwellin protein family

“…Zm KWL4 (Uniprot: A0A1D6GNR6) corresponds to Kwl2-2e and Zm KWL6 as well as Zm KWL12 are identified as BL proteins. Similarly, a fungal rust effector protein that suppresses cell death in plants was found to be a BL protein as well ( Jaswal et al., 2021 ). The structure from Actinidia deliciosa (PDB: 4X9U/Uniprot: P84527) was not recovered as the species is not part of the data set ( Offermann et al., 2015 ).…”

A decade after the first Pucciniales genomes: A bibliometric snapshot of (post) genomics studies in three model rust fungi

“…That was expected as haustoria are key infection structures that invaginate host cells, which have been, and still are, highly investigated in plant pathology ( Hahn and Mendgen, 1997 ; Garnica et al, 2014 ; Bozkurt and Kamoun, 2020 ). Interestingly, the word chloroplast also appears frequently, as eight RPGs collectively reported 11 candidate effector proteins that target chloroplasts ( Petre et al, 2015 , 2016a , b ; Germain et al, 2018 ; Xu et al, 2019 ; Andac et al, 2020 ; Ozketen et al, 2020 ; Jaswal et al, 2021 ) ( Supplementary Dataset 1 – columns U–W). Chloroplasts emerge as important actors of plant immunity, and the list of pathogen effectors that target chloroplast rapidly expands ( Kretschmer et al, 2019 ; Gao et al, 2020 ; Littlejohn et al, 2021 ; Savage et al, 2021 ).…”