Cytokinins Induce Prehaustoria Coordinately with Quinone Signals in the Parasitic Plant Striga hermonthica

Orobanchaceae parasitic plants are major threats to global food security, causing severe agricultural damage worldwide. Parasitic plants derive water and nutrients from their host plants through multicellular organs called haustoria. The formation of a prehaustorium, a primitive haustorial structure, is provoked by host-derived haustorium-inducing factors (HIFs). Quinones, including 2,6-dimethoxy-p-benzoquinone (DMBQ), are of the most potent HIFs for various species in Orobanchaceae, but except non-photosynthetic holoparasites, Phelipanche and Orobanche spp. Instead, cytokinin (CK) phytohormones were reported to induce prehaustoria in Phelipanche ramosa. However, little is known about whether CKs act as HIFs in the other parasitic species to date. Moreover, the signaling pathways for quinones and CKs in prehaustorium induction are not well understood. This study shows that CKs act as HIFs in the obligate parasite Striga hermonthica but not in the facultative parasite Phtheirospermum japonicum. Using chemical inhibitors and marker gene expression analysis, we demonstrate that CKs activate prehaustorium formation through a CK-specific signaling pathway that overlaps with the quinone HIF pathway at downstream in S. hermonthica. Moreover, host root exudates activated S. hermonthica CK biosynthesis and signaling genes, and DMBQ and CK inhibitors perturbed the prehaustorium-inducing activity of exudates, indicating that host root exudates include CKs. Our study reveals the importance of CKs for prehaustorium formation in obligate parasitic plants

Growth effect of polyphenols on SEA-producing strain.

<p>(A) hydrolyzable tannins and (B) procyanidins. Values represent the mean ± SD for three independent experiments. The final concentration of polyphenol (mg/mL) is indicated between brackets.</p

Direct reactivity of polyphenols to SEA.

<p>(A) hydrolyzable tannins (0.25 mg/mL) and (B) procyanidins (0.25–0.50 mg/mL). Values represent the mean ± SD for three independent experiments. * represents <i>p</i> < 0.05 compared with the control. (); final concentration (mg/mL).</p

Mean minimum inhibitory concentration (MIC (mg/mL)) in test samples against <i>Staphylococcus aureus</i> C-29.

<p>Mean minimum inhibitory concentration (MIC (mg/mL)) in test samples against <i>Staphylococcus aureus</i> C-29.</p

Alteration of aluminum tolerance mediated by insertion of same transposable element at different sites in the upstream region of <i>HvAACT1</i> in Japanese barley accessions

Aluminum (Al) toxicity is a major limiting factor for crop production in acid soils. Barley is highly sensitive to Al, so the genetic improvement of its Al tolerance is required. However, useful breeding materials and genetic factors for improving its tolerance are remain largely unclear. Here, we compared the Al tolerance of ‘Minorimugi’ and ‘Fibersnow,’ both six-rowed hulled barley cultivars grown mainly in northern Japan, using relative root length (RRL) as an index, and found that Minorimugi had higher tolerance. Quantitative trait locus (QTL) analysis using recombinant inbred lines (RILs) derived from the two cultivars detected a major QTL at the HvAACT1 (Al-ACTIVATED CITRATE TRANSPORTER 1) locus that explained approximately 36% of the variance. The PCR amplification analysis revealed a 1-kb transposable element (TE) insertion at −1.9 kb in the upstream region of HvAACT1 in Minorimugi that enhances HvAACT1 expression. The TE has the same nucleotide sequence as one previously found at −4.8 kb in the upstream region of HvAACT1 in ‘Murasakimochi,’ which is an Al tolerant cultivar. In the Japanese barley population, the Murasakimochi-type HvAACT1 upstream allele is shared mainly among barley accessions developed in the Shikoku area, while the Minorimugi-type allele is shared mainly among accessions developed in the Hokuriku and Nagano area. This geographic difference indicates that both alleles are shared among different subpopulations in Japanese barley, which may be advantageous for growth in acid soils. Our results provide information about a new allele of the HvAACT1 upstream region and potential breeding materials for improving the Al tolerance of barley.</p