Boron (B) toxicity in Citrus is a common physiological disorder leading to reductions in both productivity and quality. Studies on how Citrus roots evade B toxicity may provide new insight into plant tolerance to B toxicity. Here, using Illumina sequencing, differentially expressed microRNAs (miRNAs) were identified in B toxicity-treated Citrus sinensis (tolerant) and C. grandis (intolerant) roots. The results showed that 37 miRNAs in C. grandis and 11 miRNAs in C. sinensis were differentially expressed when exposed to B toxicity. Among them, miR319, miR171, and miR396g-5p were confirmed via 5′-RACE and qRT-PCR to target a myeloblastosis (MYB) transcription factor gene, a SCARECROW-like protein gene, and a cation transporting ATPase gene, respectively. Maintenance of SCARECROW expression in B treated Citrus roots might fulfill stem cell maintenance, quiescent center, and endodermis specification, thus allowing regular root elongation under B-toxic stress. Down-regulation of MYB due to up-regulation of miR319 in B toxicity-treated C. grandis roots might decrease the number of root tips, thereby dramatically changing root system architecture. Our findings suggested that miR319 and miR171 play a pivotal role in Citrus adaptation to long-term B toxicity by targeting MYB and SCARECROW, respectively, both of which are responsible for root growth and development.

Summary: The mechanisms underlying plant tolerance to boron (B) excess are far from fully understood. Here we characterized the role of the miR397‐CsiLAC4/CsiLAC17 (from Citrus sinensis) module in regulation of B flow. Live‐cell imaging techniques were used in localization studies. A tobacco transient expression system tested modulations of CsiLAC4 and CsiLAC17 by miR397. Transgenic Arabidopsis were generated to analyze the biological functions of CsiLAC4 and CsiLAC17. CsiLAC4’s role in xylem lignification was determined by mRNA hybridization and cytochemistry. In situ B distribution was analyzed by laser ablation inductively coupled plasma mass spectrometry. CsiLAC4 and CsiLAC17 are predominantly localized in the apoplast of tobacco epidermal cells. Overexpression of CsiLAC4 in Arabidopsis improves the plants’ tolerance to boric acid excess by triggering high‐B‐dependent lignification of the vascular system’s cell wall and reducing free B content in roots and shoots. In Citrus, CsiLAC4 is expressed explicitly in the xylem parenchyma and is modulated by B‐responsive miR397. Upregulation of CsiLAC4 in Citrus results in lignification of the xylem cell walls, restricting B flow from xylem vessels to the phloem. CsiLAC4 contributes to plant tolerance to boric acid excess via high‐B‐dependent lignification of cell walls, which set up a ‘physical barrier’ preventing B flow.

Tomato cultivation is seriously affected by infection from Botrytis cinerea. The safe and effective control of tomato gray mold remains elusive. Plant-related microbial communities regulate not only plant metabolism but also plant immune systems. In this study, we observed that Selenium application in soil combined with foliar spraying of methyl jasmonate could reduce Botrytis cinerea infection in tomato fruits and leaves and improve tomato fruit quality. The infection rate of leaves decreased from 42.19% to 25.00%, and the vitamin C content increased by 22.14%. The bacterial community structure of the tomato was studied by using amplicon sequencing technology. The leaf bacterial alpha diversity of tomatoes treated with Se plus methyl jasmonate was significantly higher than that of the control. Then we isolated five strains antagonistic to Botrytis cinerea in vitro from tomato leaves in the treatment of Se plus methyl jasmonate. The antagonistic strains were identified as Bacillus subtilis and Bacillus velezensis. Spraying mixed antagonistic strain suspension significantly inhibited the diameter of Botrytis cinerea with an inhibition rate of 40.99%. This study revealed the key role of plant-beneficial bacteria recruited by Se combined with methyl jasmonate in improving tomato plant disease resistance. These findings may benefit our understanding of the new regulation of microorganisms on Botrytis cinerea.

Sclerotinia sclerotiorum is a broad-spectrum necrotrophic phytopathogen that can infect many plant species worldwide. The application of fungicides is a common measure for controlling Sclerotinia sclerotiorum. Due to the risk of developing resistance to fungicides, it is imperative to find ways to be environmentally friendly and even effective. Using bioactive compounds in plants to reduce the amounts of fungicides has become a clean and sustainable strategy of controlling Sclerotinia sclerotiorum. Our study found that selenium in soil mediated the phenylacetic acid-related metabolic pathway in oilseed rape and reduced the incidence rate of Sclerotinia sclerotiorum. The growth-inhibition rates of Sclerotinia sclerotiorum were observed at 25.82%, 19.67%, and 52.61% for treatments of 0.8 mg·L⁻¹ dimethachlon, 0.1 mg·mL⁻¹ phenylacetic acid, and dimethachlon (0.8 mg·L⁻¹) + phenylacetic acid (0.1 mg·mL⁻¹), respectively. Phenylacetic acid reduced the application amount of dimethachlon and enhanced the inhibition effect for Sclerotinia sclerotiorum. Results also suggested that phenylacetic acid severely damaged the morphological structure, changed the electrical conductivity, and reduced the capacity of acid production and oxalic acid secretion of Sclerotinia sclerotiorum mycelium. Further studies revealed that phenylacetic acid increased the gene-expression level of Ssodc1, Ssodc2, CWDE2 and CWDE10 in mycelium while decreasing the expression level of SsGgt1, and phenylacetic acid + dimethachlon reduced the relative expression level of SsBil. These findings verified that phenylacetic acid could partially replace the amount of dimethachlon, as well as enhance the prevention of Sclerotinia sclerotiorum by dimethachlon, which provides evidence for developing an environment-friendly method for Sclerotinia sclerotiorum control.