Authors: Javier Lidoy, Javier Rivero, Živa Ramšak, Marko Petek, Maja Križnik, Victor Flors, Juan Antonio Lopez-Raez, Ainhoa Martínez-Medina, Kristina Gruden and María J Pozo.

bioRxiv (2024)

Abstract: "Root colonization by certain beneficial microbes can prime plant defenses aboveground, modifying plant responses to potential attackers. Arbuscular mycorrhizal (AM) fungi establish mutualistic symbiosis with most plant species, usually enhancing plant resistance to biotic stresses, leading to Mycorrhiza-Induced Resistance (MIR). Still, our knowledge of the complex molecular regulation leading to MIR is very limited. Here we show that the AM fungus Funneliformis mosseae protects tomato plants against two different chewing herbivores, Spodoptera exigua and Manduca sexta, and we explore the underlying molecular mechanism. We explore the impact of AM symbiosis on the plant response to the herbivores through genome-wide transcriptional profiling, followed by bioinformatics network analyses and functional bioassays. Herbivore-triggered JA-regulated defenses were primed in leaves of mycorrhizal plants, while ET biosynthesis and signaling was also higher both before and after herbivory. We hypothesized that fine-tuned ET signaling is required for the primed defensive response leading to MIR in mycorrhizal plants. We followed analytical, functional, and genetic approaches to test this hypothesis and get mechanistic insights into the ET signaling in MIR. ET is a complex regulator of plant responses to stress, and although ET is generally considered a negative regulator of plant defenses against herbivory, tomato lines deficient in ET synthesis or perception could not develop MIR against either herbivore. Thus, we demonstrate that hormone crosstalk is central to the priming of plant immunity by beneficial microbes, with ET fine-tuning being essential for the primed JA biosynthesis and boosted defenses leading to MIR in tomato."

Authors: Changan Zhu, Beiyu Jing, Teng Lin, Xinyan Li, Min Zhang, Yanhong Zhou, Jingquan Yu and Zhangjian Hu.

One-sentence summary: A tomato calcium-dependent protein kinase controls soluble sugar accumulation, which enhances drought tolerance, by phosphorylating a tonoplast sugar transporter.

Abstract: "Drought is a major environmental stress threatening plant growth and productivity. Calcium-dependent protein kinases (CPKs) are plant-specific Ca2+ sensors with multifaceted roles in signaling drought responses. Nonetheless, the mechanisms underpinning how CPKs transmit downstream drought signaling remain unresolved. Through genetic investigations, our study unveiled that knocking out CPK27 reduced drought tolerance in tomato (Solanum lycopersicum) plants and impaired abscisic acid (ABA)-orchestrated plant response to drought stress. Proteomics and phosphoproteomics revealed that CPK27-dependent drought-induced proteins were highly associated with the sugar metabolism pathway, which was further verified by reduced soluble sugar content in the cpk27 mutant under drought conditions. Using protein–protein interaction assays and phosphorylation assessments, we demonstrated that CPK27 directly interacted with and phosphorylated tonoplast sugar transporter 2 (TST2), promoting intercellular soluble sugar accumulation during drought stress. Furthermore, Ca2+ and ABA enhanced CPK27-mediated interaction and phosphorylation of TST2, thus revealing a role of TST2 in tomato plant drought tolerance. These findings extend the toolbox of potential interventions for enhancing plant drought stress tolerance and provide a target to improve drought tolerance by manipulating CPK27-mediated soluble sugar accumulation for rendering drought tolerance in a changing climate."

Authors: Ling Liu, Ying Gong, Baba Salifu Yahaya, Yushu Chen, Dengke Shi, Fangyuan Liu, Junlin Gou, Zhanmei Zhou, Yanli Lu and Fengkai Wu.

Plant Molecular Biology (2024)

Abstract: "Prolonged exposure to abiotic stresses causes oxidative stress, which affects plant development and survival. In this research, the overexpression of ZmARF1 improved tolerance to low Pi, drought and salinity stresses. The transgenic plants manifested tolerance to low Pi by their superior root phenotypic traits: root length, root tips, root surface area, and root volume, compared to wide-type (WT) plants. Moreover, the transgenic plants exhibited higher root and leaf Pi content and upregulated the high affinity Pi transporters PHT1;2 and phosphorus starvation inducing (PSI) genes PHO2 and PHR1 under low Pi conditions. Transgenic Arabidopsis displayed tolerance to drought and salt stress by maintaining higher chlorophyll content and chlorophyll fluorescence, lower water loss rates, and ion leakage, which contributed to the survival of overexpression lines compared to the WT. Transcriptome profiling identified a peroxidase gene, POX, whose transcript was upregulated by these abiotic stresses. Furthermore, we confirmed that ZmARF1 bound to the auxin response element (AuxRE) in the promoter of POX and enhanced its transcription to mediate tolerance to oxidative stress imposed by low Pi, drought and salt stress in the transgenic seedlings. These results demonstrate that ZmARF1 has significant potential for improving the tolerance of crops to multiple abiotic stresses."

Authors: Magdalena Korek, R. Glen Uhrig and Marek Marzec.

Journal of Applied Genetics (2024)

Abstract: "Strigolactones (SLs) are plant hormones that play a crucial role in regulating various aspects of plant architecture, such as shoot and root branching. However, the knowledge of SL-responsive genes and transcription factors (TFs) that control the shaping of plant architecture remains elusive. Here, transcriptomic analysis was conducted using the SL-insensitive barley mutant hvd14.d (carried mutation in SL receptor DWARF14, HvD14) and its wild-type (WT) to unravel the differences in gene expression separately in root and shoot tissues. This approach enabled us to select more than six thousand SL-dependent genes that were exclusive to each studied organ or not tissue-specific. The data obtained, along with in silico analyses, found several TFs that exhibited changed expression between the analyzed genotypes and that recognized binding sites in promoters of other identified differentially expressed genes (DEGs). In total, 28 TFs that recognize motifs over-represented in DEG promoters were identified. Moreover, nearly half of the identified TFs were connected in a single network of known and predicted interactions, highlighting the complexity and multidimensionality of SL-related signalling in barley. Finally, the SL control on the expression of one of the identified TFs in HvD14- and dose-dependent manners was proved. Obtained results bring us closer to understanding the signalling pathways regulating SL-dependent plant development."

Authors: Ying Li, Wenmin Yuan, Jialuo Peng, Jisheng Ju, Pingjie Ling, Xuefeng Guo, Junning Yang, Qi Ma, Hai Lin, Jilian Li, Caixiang Wang and Junji Su.

Plant Cell Reports (2024)

Key message: The silencing of GhGASA14 and the identification of superior allelic variation in its coding region indicate that GhGASA14 may positively regulate flowering and the response to GA3. 

Abstract: "Gibberellic acid-stimulated Arabidopsis (GASA), a member of the gibberellin-regulated short amino acid family, has been extensively investigated in several plant species and found to be critical for plant growth and development. However, research on this topic in cotton has been limited. In this study, we identified 38 GhGASAs that were dispersed across 18 chromosomes in upland cotton, and all of these genes had a GASA core domain. Transcriptome expression patterns and qRT-PCR results revealed that GhGASA9 and GhGASA14 exhibited upregulated expression not only in the floral organs but also in the leaves of early-maturing cultivars. The two genes were functionally characterized by virus-induced gene silencing (VIGS), and the budding and flowering times after silencing the target genes were later than those of the control (TRV:00). Compared with that in the water-treated group (MOCK), the flowering period of the different fruiting branches in the GA3-treated group was more concentrated. Interestingly, allelic variation was detected in the coding sequence of GhGASA14 between early-maturing and late‐maturing accessions, and the frequency of this favorable allele was greater in high-latitude cotton cultivars than in low-latitude ones. Additionally, a significant linear relationship was observed between the expression level of GhGASA14 and flowering time among the 12 upland cotton accessions. Taken together, these results indicated that GhGASA14 may positively regulate flowering time and respond to GA3. These findings could lead to the use of valuable genetic resources for breeding early-maturing cotton cultivars in the future."

Authors: Minmin Yang, Yixuan Wang, Chong Chen, Xin Xin, Shanshan Dai, Chen Meng and Nana Ma.

One-sentence summary: A WRKY transcription factor enhances tomato defense against Pseudomonas syringae by decreasing P. syringae-induced accumulation of free indole-3-acetic acid.

Abstract: "The hemibiotrophic bacterial pathogen Pseudomonas syringae infects a range of plant species and causes enormous economic losses. Auxin and WRKY transcription factors play crucial roles in plant responses to P. syringae, but their functional relationship in plant immunity remains unclear. Here, we characterized tomato (Solanum lycopersicum) SlWRKY75, which promotes defenses against P. syringae pv. tomato (Pst) DC3000 by regulating plant auxin homeostasis. Overexpressing SlWRKY75 resulted in low free indole-3-acetic acid (IAA) levels, leading to attenuated auxin signaling, decreased expansin transcript levels, upregulated expression of PATHOGENESIS-RELATED GENES (PRs) and NONEXPRESSOR OF PATHOGENESIS-RELATED GENE 1 (NPR1), and enhanced tomato defenses against Pst DC3000. RNA interference-mediated repression of SlWRKY75 increased tomato susceptibility to Pst DC3000. Yeast one-hybrid, electrophoretic mobility shift assays, and luciferase activity assays suggested that SlWRKY75 directly activates the expression of GRETCHEN HAGEN 3.3 (SlGH3.3), which encodes an IAA-amido synthetase. SlGH3.3 enhanced tomato defense against Pst DC3000 by converting free IAA to the aspartic acid (Asp)-conjugated form IAA-Asp. In addition, SlWRKY75 interacted with a tomato valine-glutamine (VQ) motif-containing protein 16 (SlVQ16) in vivo and in vitro. SlVQ16 enhanced SlWRKY75-mediated transcriptional activation of SlGH3.3 and promoted tomato defense responses to Pst DC3000. Our findings illuminate a mechanism in which the SlVQ16–SlWRKY75 complex participates in tomato pathogen defense by positively regulating SlGH3.3-mediated auxin homeostasis."