S-Adenosyl-L-methionine synthetase (SAM-s) catalyzes the biosynthesis of SAM from ATP and L-methionine. Despite extensive research with many organisms, its role in Streptomyces sp. remains unclear. In the present study, the putative SAM-s gene was isolated from a spectinomycin producer, Streptomyces spectabilis. The purified protein from the transformed Escherichia coli with the isolated gene synthesized SAM from L-methionine and ATP in vitro, strongly indicating that the isolated gene indeed encoded the SAM-s protein.The overexpression of the SAM-s gene in Streptomyces lividans TK23 inhibited sporulation and aerial mycelium formation but enhanced the production of actinorhodin in both agar plates and liquid media. Surprisingly, the overexpressed SAM was proven by Northern analysis to increase the production of actinorhodin through the induction of actII-ORF4, a transcription activator of actinorhodin biosynthetic gene clusters. In addition, we found that a certain level of intracellular SAM is critical for the induction of antibiotic biosynthetic genes, since the control strain harboring only the plasmid DNA did not show any induction of actII-ORF4 until it reached a certain level of SAM in the cell. From these results, we concluded that the SAM plays important roles as an intracellular factor in both cellular differentiation and antibiotic production in Streptomyces sp.

The mutualistic, endophytic fungus Piriformospora indica has been shown to confer biotic and abiotic stress tolerance to host plants. In this study, we investigated the impact of P. indica on the growth of Arabidopsis plants under normal and salt stress conditions. Our results demonstrate that P. indica colonization increases plant biomass, lateral roots density, and chlorophyll content under both conditions. Colonization with P. indica under salt stress was accompanied by a lower Na/K ratio and less pronounced accumulation of anthocyanin, compared to control plants. Moreover, P. indica colonized roots under salt stress showed enhanced transcript levels of the genes encoding the high Affinity Potassium Transporter 1 (HKT1) and the inward-rectifying K channels KAT1 and KAT2, which play key roles in regulating Na and K homeostasis. The effect of P. indica colonization on AtHKT1;1 expression was also confirmed in the Arabidopsis line gl1-HKT:AtHKT1;1 that expresses an additional AtHKT1;1 copy driven by the native promoter. Colonization of the gl1-HKT:AtHKT1;1 by P. indica also increased lateral roots density and led to a better Na/K ratio, which may be attributed to the observed increase in KAT1 and KAT2 transcript levels. Our findings demonstrate that P. indica colonization promotes Arabidopsis growth under salt stress conditions and that this effect is likely caused by modulation of the expression levels of the major Na and K ion channels, which allows establishing a balanced ion homeostasis of Na/K under salt stress conditions.

Striga hermonthica is a root parasitic plant that infests cereals, decimating yields, particularly in sub‐Saharan Africa. For germination, Striga seeds require host‐released strigolactones that are perceived by the family of HYPOSENSITIVE to LIGHT (ShHTL) receptors. Inhibiting seed germination would thus be a promising approach for combating Striga. However, there are currently no strigolactone antagonists that specifically block ShHTLs and do not bind to DWARF14, the homologous strigolactone receptor of the host. Here, we show that the octyl phenol ethoxylate Triton X‐100 inhibits S. hermonthica seed germination without affecting host plants. High‐resolution X‐ray structures reveal that Triton X‐100 specifically plugs the catalytic pocket of ShHTL7. ShHTL7‐specific inhibition by Triton X‐100 demonstrates the dominant role of this particular ShHTL receptor for Striga germination. Our structural analysis provides a rationale for the broad specificity and high sensitivity of ShHTL7, and reveals that strigolactones trigger structural changes in ShHTL7 that are required for downstream signaling. Our findings identify Triton and the related 2‐[4‐(2,4,4‐trimethylpentan‐2‐yl)phenoxy]acetic acid as promising lead compounds for the rational design of efficient Striga‐specific herbicides.

Abscisic acid (ABA) is an important phytohormone that controls several plant processes such as seed germination, seedling growth, and abiotic stress response. Here, we report that AtYak1 plays an important role in ABA signaling and postgermination growth in Arabidopsis. AtYak1 knockout mutant plants were hyposensitive to ABA inhibition of seed germination, cotyledon greening, seedling growth, and stomatal movement. atyak1-1 mutant plants display reduced drought stress resistance, as evidenced by water loss rate and survival rate. Molecular genetic analysis revealed that AtYak1 deficiency led to elevated expression of stomatal-related gene, MYB60, and down-regulation of several stress-responsive genes. Altogether, these results indicate that AtYak1 plays a role as a positive regulator in ABA-mediated drought response in Arabidopsis.