Kaminaka, H. | bioRxiv Science

bioRxiv2021

Conservation and diversity in transcriptional responses among host plants forming distinct arbuscular mycorrhizal morphotypes

O_LIThe morphotype of arbuscular mycorrhizal (AM) roots is distinct mostly depending on AM host species: Arum, Paris, and Intermediate types. We previously reported that gibberellin (GA) promotes the establishment of Paris-type AM symbiosis in Eustoma grandiflorum despite its negative effects on Arum-type AM symbiosis in model plants. However, the molecular mechanisms underlying the differential effects of GA on different morphotypes, including Intermediate-type AM symbiosis, remain elusive. C_LIO_LIComparative transcriptomics revealed that several symbiosis-related genes were transcriptionally promoted upon AM fungal colonization in Lotus japonicus (Arum-type), Daucus carota (Intermediate-type), and E. grandiflorum (Paris-type). Interestingly, upon GA treatment, the fungal colonization levels and expression of symbiosis-related genes were suppressed in L. japonicus and D. carota but were promoted in E. grandiflorum. C_LIO_LIExogenous GA transcriptionally inhibited the biosynthetic process of a host-derived signal molecule involved in AM symbiosis, strigolactone, in L. japonicus and E. grandiflorum. Additionally, disaccharides mainly metabolized in AM roots would be different between L. japonicus and D. carota/E. grandiflorum. C_LIO_LIThis study uncovered the conserved transcriptional responses during mycorrhization and diverse responses to GA in AM roots with distinct morphotypes among phylogenetically distant host plants. C_LI

plant biology↗

bioRxiv2020

Arabidopsis SMN2/HEN2, encoding DEAD-box RNA helicase, governs proper expression of the resistance gene SMN1/RPS6 and is involved in dwarf, autoimmune phenotypes of mekk1 and mpk4

In Arabidopsis thaliana, a mitogen-activated protein kinase pathway, MEKK1-MKK1/MKK2-MPK4, is important for basal resistance, and disruption of this pathway results in dwarf, autoimmune phenotypes. To elucidate the complex mechanisms activated by the disruption of this pathway, we have previously developed a mutant screening system based on a dwarf autoimmune line that overexpressed the N-terminal regulatory domain of MEKK1. Here, we report that the second group of mutants, smn2, had defects in the SMN2 gene, encoding a DEAD-box RNA helicase. SMN2 is identical to HEN2, whose function is vital for the nuclear RNA exosome because it provides non-ribosomal RNA specificity for RNA turnover, RNA quality control, and RNA processing. Aberrant SMN1/RPS6 transcripts were detected in smn2 and hen2 mutants. Disease resistance against Pseudomonas syringae pv. tomato DC3000 (hopA1), which is conferred by SMN1/RPS6, was decreased in smn2 mutants, suggesting a functional connection between SMN1/RPS6 and SMN2/HEN2. We produced double mutants mekk1smn2 and mpk4smn2 to determine whether the smn2 mutations suppress the dwarf, autoimmune phenotypes of the mekk1 and mpk4 mutants, as the smn1 mutations do. As expected, the mekk1 and mpk4 phenotypes were suppressed by the smn2 mutations. These results suggested that SMN2 is involved in proper function of SMN1/RPS6. The GO enrichment analysis using RNA-seq data showed that defense genes were downregulated in smn2, suggesting positive contribution of SMN2 to genome-wide expression of defense-related genes. In conclusion, this study provides novel insight into plant immunity via SMN2/HEN2, an essential component of the nuclear RNA exosome.

plant biology↗