Cytokinin-deficient Chlamydomonas reinhardtii CRISPR-Cas9 mutants show reduced ability to prime resistance of tobacco against bacterial infection.

Although microalgae have only recently been recognized as part of the plant and soil microbiome, their application as biofertilizers has a tradition in sustainable crop production. Under consideration of their ability to produce the plant growth-stimulating hormone cytokinin (CK), known to also induce pathogen resistance, we have assessed the biocontrol ability of CK-producing microalgae. All pro- and eukaryotic CK-producing microalgae tested were able to enhance the tolerance of tobacco against Pseudomonas syringae pv. tabaci (PsT) infection. Since Chlamydomonas reinhardtii (Cre) proved to be the most efficient, we functionally characterized its biocontrol ability. We employed the CRISPR-Cas9 system to generate the first knockouts of CK biosynthetic genes in microalgae. Specifically, we targeted Cre Lonely Guy (LOG) and isopentenyltransferase (IPT) genes, the key genes of CK biosynthesis. While Cre wild-type exhibits a strong protection, the CK-deficient mutants have a reduced ability to induce plant defence. The degree of protection correlates with the CK levels, with the IPT mutants showing less protection than the LOG mutants. Gene expression analyses showed that Cre strongly stimulates tobacco resistance through defence gene priming. This study functionally verifies that Cre primes defence responses with CK, which contributes to the robustness of the effect. This work contributes to elucidate microalgae-mediated plant defence priming and identifies the role of CKs. In addition, these results underscore the potential of CK-producing microalgae as biologicals in agriculture by combining biofertilizer and biocontrol ability for sustainable and environment-friendly crop management.

Heat Stress and Plant-Biotic Interactions: Advances and Perspectives.

Climate change presents numerous challenges for agriculture, including frequent events of plant abiotic stresses such as elevated temperatures that lead to heat stress (HS). As the primary driving factor of climate change, HS threatens global food security and biodiversity. In recent years, HS events have negatively impacted plant physiology, reducing plant's ability to maintain disease resistance and resulting in lower crop yields. Plants must adapt their priorities toward defense mechanisms to tolerate stress in challenging environments. Furthermore, selective breeding and long-term domestication for higher yields have made crop varieties vulnerable to multiple stressors, making them more susceptible to frequent HS events. Studies on climate change predict that concurrent HS and biotic stresses will become more frequent and severe in the future, potentially occurring simultaneously or sequentially. While most studies have focused on singular stress effects on plant systems to examine how plants respond to specific stresses, the simultaneous occurrence of HS and biotic stresses pose a growing threat to agricultural productivity. Few studies have explored the interactions between HS and plant-biotic interactions. Here, we aim to shed light on the physiological and molecular effects of HS and biotic factor interactions (bacteria, fungi, oomycetes, nematodes, insect pests, pollinators, weedy species, and parasitic plants), as well as their combined impact on crop growth and yields. We also examine recent advances in designing and developing various strategies to address multi-stress scenarios related to HS and biotic factors.

Synergy between virus and three kingdom pathogens, fungus, bacterium and virus is lost in rice mutant lines of OsRDR1/6.

Co-infection, caused by multiple pathogen attacks on an organism, can lead to disease development or immunity. This complex interaction can be synergetic, co-existing, or antagonistic, ultimately influencing disease severity. The interaction between fungus, bacterium, and virus (three kingdom pathogens) is most prevalent. However, the underlying mechanisms of co-infection need to be explored further. In this study, we investigated the co-infection phenomenon in rice plants exposed to multiple pathogen species, specifically Rice necrosis mosaic virus (RNMV) and rice blast fungus (Magnaporthe oryzae, MO), bacterial leaf blight (Xanthomonas oryzae pv. oryzae, XO) or Cucumber mosaic virus (CMV). Our research showed that RNMV interacts synergistically with MO, XO, or CMV, increasing pathogen growth and lesion size. These findings suggest positive synergy in RNMV co-infections with three kingdom pathogens, increasing accumulation and symptoms. Additionally, to investigate the role of RNAi in pathogen synergism, we analyzed rice mutant lines deficient in RNA-dependent RNA polymerase 1 (OsRDR1) or 6 (OsRDR6). Notably, we observed the loss of synergy in each mutant line, highlighting the crucial role of OsRDR1 and OsRDR6 in maintaining the positive interaction between RNMV and three kingdom pathogens. Hence, our study emphasized the role of the RNA silencing pathway in the intricate landscape of pathogen interactions; the study's outcome could be applied to understand the plant defense response to improve crop yields.

Gene Coexpression Analysis Identifies Genes Associated with Chlorophyll Content and Relative Water Content in Pearl Millet.

Pearl millet is a significant crop that is tolerant to abiotic stresses and is a staple food of arid regions. However, its underlying mechanisms of stress tolerance are not fully understood. Plant survival is regulated by the ability to perceive a stress signal and induce appropriate physiological changes. Here, we screened for genes regulating physiological changes such as chlorophyll content (CC) and relative water content (RWC) in response to abiotic stress by using "weighted gene coexpression network analysis" (WGCNA) and clustering changes in physiological traits, i.e., CC and RWC associated with gene expression. Genes' correlations with traits were defined in the form of modules, and different color names were used to denote a particular module. Modules are groups of genes with similar patterns of expression, which also tend to be functionally related and co-regulated. In WGCNA, the dark green module (7082 genes) showed a significant positive correlation with CC, and the black (1393 genes) module was negatively correlated with CC and RWC. Analysis of the module positively correlated with CC highlighted ribosome synthesis and plant hormone signaling as the most significant pathways. Potassium transporter 8 and monothiol glutaredoxin were reported as the topmost hub genes in the dark green module. In Clust analysis, 2987 genes were found to display a correlation with increasing CC and RWC. Furthermore, the pathway analysis of these clusters identified the ribosome and thermogenesis as positive regulators of RWC and CC, respectively. Our study provides novel insights into the molecular mechanisms regulating CC and RWC in pearl millet.