Endoplasmic reticulum-derived bodies enable a single-cell chemical defense in Brassicaceae plants

アブラナ科植物の新しい防虫機構の発見 --細胞小器官ERボディが支える新型カラシ油爆弾--. 京都大学プレスリリース. 2020-01-15.Brassicaceae plants have a dual-cell type of chemical defense against herbivory. Here, we show a novel single-cell defense involving endoplasmic reticulum (ER)-derived organelles (ER bodies) and the vacuoles. We identify various glucosinolates as endogenous substrates of the ER-body β-glucosidases BGLU23 and BGLU21. Woodlice strongly prefer to eat seedlings of bglu23 bglu21 or a glucosinolate-deficient mutant over wild-type seedlings, confirming that the β-glucosidases have a role in chemical defense: production of toxic compounds upon organellar damage. Deficiency of the Brassicaceae-specific protein NAI2 prevents ER-body formation, which results in a loss of BGLU23 and a loss of resistance to woodlice. Hence, NAI2 that interacts with BGLU23 is essential for sequestering BGLU23 in ER bodies and preventing its degradation. Artificial expression of NAI2 and BGLU23 in non-Brassicaceae plants results in the formation of ER bodies, indicating that acquisition of NAI2 by Brassicaceae plants is a key step in developing their single-cell defense system

Loss of genes for DNA recombination and repair in the reductive genome evolution of thioautotrophic symbionts of Calyptogena clams

BACKGROUND: Two Calyptogena clam intracellular obligate symbionts, Ca. Vesicomyosocius okutanii (Vok; C. okutanii symbiont) and Ca. Ruthia magnifica (Rma; C. magnifica symbiont), have small genomes (1.02 and 1.16 Mb, respectively) with low G+C contents (31.6% and 34.0%, respectively) and are thought to be in an ongoing stage of reductive genome evolution (RGE). They lack recA and some genes for DNA repair, including mutY. The loss of recA and mutY is thought to contribute to the stabilization of their genome architectures and GC bias, respectively. To understand how these genes were lost from the symbiont genomes, we surveyed these genes in the genomes from 10 other Calyptogena clam symbionts using the polymerase chain reaction (PCR). RESULTS: Phylogenetic trees reconstructed using concatenated 16S and 23S rRNA gene sequences showed that the symbionts formed two clades, clade I (symbionts of C. kawamurai, C. laubieri, C. kilmeri, C. okutanii and C. soyoae) and clade II (those of C. pacifica, C. fausta, C. nautilei, C. stearnsii, C. magnifica, C. fossajaponica and C. phaseoliformis). recA was detected by PCR with consensus primers for recA in the symbiont of C. phaseoliformis. A detailed homology search revealed a remnant recA in the Rma genome. Using PCR with a newly designed primer set, intact recA or its remnant was detected in clade II symbionts. In clade I symbionts, the recA coding region was found to be mostly deleted. In the Rma genome, a pseudogene of mutY was found. Using PCR with newly designed primer sets, mutY was not found in clade I symbionts but was found in clade II symbionts. The G+C content of 16S and 23S rRNA genes in symbionts lacking mutY was significantly lower than in those with mutY. CONCLUSIONS: The extant Calyptogena clam symbionts in clade II were shown to have recA and mutY or their remnants, while those in clade I did not. The present results indicate that the extant symbionts are losing these genes in RGE, and that the loss of mutY contributed to the GC bias of the genomes during their evolution