Physiological and autophagy evaluation of different pear varieties (Pyrus spp.) in response to Botryosphaeria dothidea infection

Ring rot disease is one of the most common diseases in pear orchards. To better understand the physiology, biochemistry and autophagic changes of different pear varieties after Botryosphaeria dothidea (B.dothidea) infection, we evaluated eight different pear varieties for B. dothidea resistance. The susceptible varieties had larger spot diameters, lower chlorophyll contents and higher malondialdehyde contents than the resistant varieties. In disease-resistant varieties, reactive oxygen species (ROS) levels were relatively lower, while the ROS metabolism (antioxidant enzyme activities and the ascorbic acid-glutathione cycle) was also maintained at higher levels, and it induced a significant upregulation of related gene expression. In addition, autophagy, as an important evaluation index, was found to have more autophagic activity in disease-resistant varieties than in susceptible varieties, suggesting that pathogen infestation drives plants to increase autophagy to defend against pathogens. In summary, the results of this study reveal that different resistant pear varieties enhance plant resistance to the disease through a series of physio-biochemical changes and autophagic activity after inoculation with B. dothidea. This study provides clear physiological and biochemical traits for pear disease resistance selection, potential genetic resources and material basis for pear disease control and disease resistance, breeding and points out the direction for research on the mechanism of pear resistance to B. dothidea.

Susceptibility and diagnostic concentration for Bacillus thuringiensis toxins and newer chemical insecticides in Spodoptera frugiperda (Lepidoptera: Noctuidae) from China

The fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae), is a cosmopolitan pest that exploits more than 350 host plants, including economically important crops such as corn, cotton and rice. Control of S. frugiperda largely relies on transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt) and spraying synthetic insecticides. Here, we established the susceptibility and diagnostic concentration for 2 Bt toxins and 5 newer insecticides in invasive populations of S. frugiperda from southeastern China. Concentrations causing 50% mortality (LC50) in ten field populations sampled in 2022 ranged from 2.13 to 19.29 and 22.43 to 71.12 ng/cm2 for Cry1Fa and Vip3Aa, and 0.83 to 5.30, 2.83 to 9.94, 0.04 to 0.23, 4.59 to 8.40, and 1.49 to 6.79 mg/liter for chlorantraniliprole, chlorfenapyr, emamectin benzoate, indoxacarb, and spinosad, respectively. Relative to the susceptible strain YJ-19, the largest resistance ratio in the field populations was 5.1, 1.6, 6.2, 3.9, 4.6, 2.2, and 3.6 for Cry1Fa, Vip3Aa, chlorantraniliprole, chlorfenapyr, emamectin benzoate, indoxacarb, and spinosad, respectively, indicating that the field populations were generally susceptible to these Bt toxins and insecticides. Based on the pooled response of the field populations, the diagnostic concentration for resistance monitoring, estimated as ca. twice the LC99, was 400 and 1,500 ng/cm2 for Cry1Fa and Vip3Aa, and 2, 40, 60, 60, and 100 mg/liter for emamectin benzoate, chlorantraniliprole, chlorfenapyr, spinosad, and indoxacarb, respectively. These results provide useful information for monitoring resistance to key Bt toxins and insecticides for the control of S. frugiperda in China.

Target of Rapamycin Mediated Ornithine Decarboxylase Antizyme Modulate Intracellular Putrescine and Ganoderic Acid Content in Ganoderma lucidum

Putrescine (Put) has been shown to play an important regulatory role in cell growth in organisms. As the primary center regulating the homeostasis of polyamine (PA) content, ornithine decarboxylase antizyme (AZ) can regulate PA content through feedback. Nevertheless, the regulatory mechanism of Put is poorly understood in fungi. Here, our analysis showed that GlAZ had a modulate effect on intracellular Put content by interacting with ornithine decarboxylase (ODC) proteins and reducing its intracellular protein levels. In addition, GlAZ upregulated the metabolic pathway of ganoderic acid (GA) biosynthesis in Ganoderma lucidum by modulating the intracellular Put content. However, a target of rapamycin (TOR) was found to promote the accumulation of intracellular Put after the GlTOR inhibitor Rap was added exogenously, and unbiased analyses demonstrated that GlTOR may promote Put production through its inhibitory effect on the level of GlAZ protein in GlTOR-GlAZ-cosilenced strains. The effect of TOR on fungal secondary metabolism was further explored, and the content of GA in the GlTOR-silenced strain after the exogenous addition of the inhibitor Rap was significantly increased compared with that in the untreated wild-type (WT) strain. Silencing of TOR in the GlTOR-silenced strains caused an increase in GA content, which returned to the WT state after replenishing Put. Moreover, the content of GA in GlTOR-GlAZ-cosilenced strains was also not different from that in the WT strain. Consequently, these results strongly indicate that GlTOR affects G. lucidum GA biosynthesis via GlAZ. IMPORTANCE Research on antizyme (AZ) in fungi has focused on the mechanism by which AZ inhibits ornithine decarboxylase (ODC). Moreover, there are existing reports on the regulation of AZ protein translation by TOR. However, little is known about the mechanisms that influence AZ in fungal secondary metabolism. Here, both intracellular Put content and GA biosynthesis in G. lucidum were shown to be regulated through protein interactions between GlAZ and GlODC. Furthermore, exploration of upstream regulators of GlAZ suggested that GlAZ was regulated by the upstream protein GlTOR, which affected intracellular Put levels and ganoderic acid (GA) biosynthesis. The results of our work contribute to the understanding of the upstream regulation of Put and provide new insights into PA regulatory systems and secondary metabolism in fungi.