Yanbing Lin

Orobanche cumana Wallr. is a root parasitic plant that causes considerable yield losses of up to 50% in sunflower Helianthus annuus plantations. The holoparasite fulfills its entire demand for water, minerals, and organic nutrients from the host’s vascular system. Agronomic practices alone are not effective in controlling this pest. This study investigated the mechanism of a verified plant growth-promoting strain, Streptomyces rochei D74, on the inhibition of the parasitism of O. cumana in a co-culture experiment. We conducted potted and sterile co-culture experiments using sunflower, O. cumana, and S. rochei D74. Our results suggest that the inoculated bacteria invoked the sunflower systemic resistance (SAR and ISR) by increasing the activity of resistance-related enzymes (SOD, POD, PPO, and PAL), the gene expression of systemic resistance marker genes (PR-1 and NPR1), ethylene synthesis genes (HACS. 1 and ACCO1), and JA synthesis genes (pin2 and lox). The expression levels of ISR marker genes (lox, HACS. 1, ACCO1, and pin2) increased by 1.66–7.91-fold in the seedling stage. Simultaneously, S. rochei D74 formed a protective layer on the sunflower root surface, preventing O. cumana from connecting to the vascular system of the sunflower roots. In addition, S. rochei D74 reduced 5DS synthesis of the strigol precursor substance, resulting in a reduction in O. cumana germination. These results demonstrated that the S. rochei D74 strain improved systemic resistance and decreased seed germination to prevent O. cumana parasitism.

Halomonas species are renowned for their production of organic compatible solutes, particularly ectoine. However, the identification of key regulatory genes governing ectoine production in Halomonas remains limited. In this study, we conducted a combined transcriptome-proteome analysis to unveil additional regulatory genes influencing ectoine biosynthesis, particularly under ultraviolet (UV) and salt conditions. NaCl induction resulted in a 20-fold increase, while UV treatment led to at least 2.5-fold increases in ectoine production. The number of overlapping genes between transcriptomic and proteomic analyses for three comparisons, i.e., non-UV with NaCl (UV0-NaCl) vs. non-UV without NaCl (UV0), UV strain 1 (UV1-NaCl) vs. UV0-NaCl, and UV strain 2 (UV2-NaCl) vs. UV0-NaCl were 137, 19, and 21, respectively. The overlapped Gene Ontology (GO) enrichments between transcriptomic and proteomic analyses include ATPase-coupled organic phosphonate, phosphonate transmembrane transporter activity, and ATP-binding cassette (ABC) transport complex in different comparisons. Furthermore, five common genes exhibited different expression patterns at mRNA and protein levels across the three comparisons. These genes included orf01280, orf00986, orf01283, orf01282 and orf01284. qPCR verification confirmed that three of the five common genes were notably under-expressed following NaCl and UV treatments. This study highlighted the potential role of these five common genes in regulating ectoine production in Halomonas strains.

Parasitic weeds, such as Orobanche and Striga, threaten crops globally. Contiguous efforts on the discovery and development of structurally novel seed germination stimulants targeting HYPOSENSITIVE TO LIGHT/KARRIKIN INSENSITIVE 2 (HTL/KAI2) have been made with the goal of weed control. Here, we demonstrate that a natural compound dehydrocostus lactone (DCL) exhibits effective "suicide germination" activity against Orobanche cumana and covalently binds to OcKAI2d2 on two catalytic serine sites with the second modification dependent on the first one. The same interactions and covalent modifications of DCL are also confirmed in AtKAI2. Further in-depth evolution analysis indicates that the proposed two catalytic sites are present throughout the streptophyte algae, hornworts, lycophytes, and seed plants. This discovery is particularly noteworthy as it signifies the first confirmation of a plant endogenous molecule directly binding to KAI2, which is valuable for unraveling the elusive identity of the KAI2 ligand and for targeting KAI2 paralogues for the development of novel germination stimulants.

Sunflower broomrape (Orobanche cumana Wallr.) has severely restricted the development of the sunflower industry in China, and more efficient and convenient control methods are urgently needed. In this experiment, we investigated the effects of N, P and silica fertilizers on the parasitism rate of O. cumana, as well as on the yield of sunflower and native microbial communities in the field. Firstly, pot experiments were conducted to select the most effective fertilization method and to determine the physiological and biochemical indexes of sunflowers. Subsequently, field application studies were carried out to determine the physiological indexes, yield, O. cumana parasitism on sunflower, and the effect on the indigenous microbial community. The results demonstrate that compared with the CNP treatment (Control), the number of parasites under the N1P5 treatment significantly decreased by 66.15%. The exogenous application of silica can significantly reduce the number of O. cumana parasites. The treatments with N1P5 (N/P = 1:5) and available SiO₂ content higher than 40 mg/kg (NS2, NS3, SF2 and SF3) significantly increased superoxide dismutase (SOD) activity and decreased malondialdehyde (MDA) content in sunflower leaves. In the field, fertilization significantly decreased the number of O. cumana parasites. The S treatment improved the native microbial community structure and enriched beneficial microorganisms, including Vicinamibacteria and Pyrinomonadaceae. Additionally, applying the S treatment significantly increased sunflower yield by 23.82% and crude protein content by 20.20%. In summary, the application of silicon fertilizer can effectively improve the host microbial community, reduce O. cumana parasitism and improve the yield and quality of sunflower.