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1. Role of heterotrimeric G-proteins in improving abiotic stress tolerance of crop plants

   Parinita Majumdar, P ; Torres Rodríguez, MD ; Pandey, S ( January 2022 , Journal of plant growth regulation)

   Sopory, SK (Ed.)

   As sessile organisms, plants are constantly exposed to a variety of environmental stresses that have detrimental effects on their growth and development, leading to major crop yield losses worldwide. To cope with adverse conditions plants have developed several adaptive mechanisms. A thorough understanding these mechanisms is critical to generate plants for the future. The heterotrimeric G-protein complex, composed of Gα, Gβ, and Gγ subunits, participates in regulation of multiple cellular signaling pathways and have multifaceted roles in regulating stress responses of plants. The complex has two functional entities, the GTP-bound Gα subunit and the Gβγ dimer, both of which by interacting with additional proteins can activate various signaling networks. The involvement of G-proteins has been shown in plants’ response to drought, salinity, extreme temperatures, heavy metal, ozone, and UV-B radiation. Due to their versatility and the number of processes modulated by them, G-proteins have emerged as key targets for generating stress tolerant crops. In this review, we provide an overview of the current knowledge of the roles of G proteins in abiotic stress tolerance, with examples from model plant Arabidopsis thaliana, where these processes are most widely studied and from additional agriculturally relevant crops, where their potential is realized for human usage. 

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2. γ-Aminobutyric acid plays a key role in plant acclimation to a combination of high light and heat stress

   https://doi.org/10.1093/plphys/kiac010  

   Balfagón, Damián ; Gómez-Cadenas, Aurelio ; Rambla, José L. ; Granell, Antonio ; de Ollas, Carlos ; Bassham, Diane C. ; Mittler, Ron ; Zandalinas, Sara I. ( January 2022 , Plant Physiology)

   Plants are frequently subjected to different combinations of abiotic stresses, such as high light (HL) intensity, and elevated temperatures. These environmental conditions pose a threat to agriculture production, affecting photosynthesis, and decreasing yield. Metabolic responses of plants, such as alterations in carbohydrates and amino acid fluxes, play a key role in the successful acclimation of plants to different abiotic stresses, directing resources toward stress responses, and suppressing growth. Here we show that the primary metabolic response of Arabidopsis (Arabidopsis thaliana) plants to HL or heat stress (HS) is different from that of plants subjected to a combination of HL and HS (HL+HS). We further demonstrate that the combined stress results in a unique metabolic response that includes increased accumulation of sugars and amino acids coupled with decreased levels of metabolites participating in the tricarboxylic acid cycle. Among the amino acids exclusively accumulated during HL+HS, we identified the nonproteinogenic amino acid γ-aminobutyric acid (GABA). Analysis of different mutants deficient in GABA biosynthesis (GLUTAMATE DESCARBOXYLASE 3 [gad3]) as well as mutants impaired in autophagy (autophagy-related proteins 5 and 9 [atg5 and atg9]), revealed that GABA plays a key role in the acclimation of plants to HL+HS, potentially by promoting autophagy. Taken together, our findings identify a role for GABA in regulating plant responses to combined stress.

    

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3. Plant responses to climate change: metabolic changes under combined abiotic stresses

   https://doi.org/10.1093/jxb/erac073  

   Zandalinas, Sara I. ; Balfagón, Damián ; Gómez-Cadenas, Aurelio ; Mittler, Ron ; Beckles, ed., Diane ( February 2022 , Journal of Experimental Botany)

   Climate change is predicted to increase the frequency and intensity of abiotic stress combinations that negatively impact plants and pose a serious threat to crop yield and food supply. Plants respond to episodes of stress combination by activating specific physiological and molecular responses, as well as by adjusting different metabolic pathways, to mitigate the negative effects of the stress combination on plant growth, development, and reproduction. Plants synthesize a wide range of metabolites that regulate many aspects of plant growth and development, as well as plant responses to stress. Although metabolic responses to individual abiotic stresses have been studied extensively in different plant species, recent efforts have been directed at understanding metabolic responses that occur when different abiotic factors are combined. In this review we examine recent studies of metabolomic changes under stress combination in different plants and suggest new avenues for the development of stress combination-resilient crops based on metabolites as breeding targets.

    

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4. Global Analysis of RNA-Dependent RNA Polymerase-Dependent Small RNAs Reveals New Substrates and Functions for These Proteins and SGS3 in Arabidopsis

   https://doi.org/10.3390/ncrna7020028  

   Hua, Xia ; Berkowitz, Nathan D. ; Willmann, Matthew R. ; Yu, Xiang ; Lyons, Eric ; Gregory, Brian D. ( June 2021 , Non-Coding RNA)

   null (Ed.)

   RNA silencing pathways control eukaryotic gene expression transcriptionally or posttranscriptionally in a sequence-specific manner. In RNA silencing, the production of double-stranded RNA (dsRNA) gives rise to various classes of 20–24 nucleotide (nt) small RNAs (smRNAs). In Arabidopsis thaliana, smRNAs are often derived from long dsRNA molecules synthesized by one of the six genomically encoded RNA-dependent RNA Polymerase (RDR) proteins. However, the full complement of the RDR-dependent smRNAs and functions that these proteins and their RNA-binding cofactors play in plant RNA silencing has not been fully uncovered. To address this gap, we performed a global genomic analysis of all six RDRs and two of their cofactors to find new substrates for RDRs and targets of the resulting RDR-derived siRNAs to uncover new functions for these proteins in plants. Based on these analyses, we identified substrates for the three RDRγ clade proteins (RDR3–5), which had not been well-characterized previously. We also identified new substrates for the other three RDRs (RDR1, RDR2, and RDR6) as well as the RDR2 cofactor RNA-directed DNA methylation 12 (RDM12) and the RDR6 cofactor suppressor of gene silencing 3 (SGS3). These findings revealed that the target substrates of SGS3 are not limited to those solely utilized by RDR6, but that this protein seems to be a more general cofactor for the RDR family of proteins. Additionally, we found that RDR6 and SGS3 are involved in the production of smRNAs that target transcripts related to abiotic stresses, including water deprivation, salt stress, and ABA response, and as expected the levels of these mRNAs are increased in rdr6 and sgs3 mutant plants. Correspondingly, plants that lack these proteins (rdr6 and sgs3 mutants) are hypersensitive to ABA treatment, tolerant to high levels of PEG8000, and have a higher survival rate under salt treatment in comparison to wild-type plants. In total, our analyses have provided an extremely data-rich resource for uncovering new functions of RDR-dependent RNA silencing in plants, while also revealing a previously unexplored link between the RDR6/SGS3-dependent pathway and plant abiotic stress responses. 

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5. Molecular basis of priming-induced acquired tolerance to multiple abiotic stresses in plants

   https://doi.org/10.1093/jxb/erac089  

   Nair, Akshay U. ; Bhukya, Durga Prasad Naik ; Sunkar, Ramanjulu ; Chavali, Sreenivas ; Allu, Annapurna Devi ; Noctor, ed., Graham ( March 2022 , Journal of Experimental Botany)

   The growth, survival, and productivity of plants are constantly challenged by diverse abiotic stresses. When plants are exposed to stress for the first time, they can capture molecular information and store it as a form of memory, which enables them to competently and rapidly respond to subsequent stress(es). This process is referred to as a priming-induced or acquired stress response. In this review, we discuss how (i) the storage and retrieval of the information from stress memory modulates plant physiological, cellular, and molecular processes in response to subsequent stress(es), (ii) the intensity, recurrence, and duration of priming stimuli influences the outcomes of the stress response, and (iii) the varying responses at different plant developmental stages. We highlight current understanding of the distinct and common molecular processes manifested at the epigenetic, (post-)transcriptional, and post-translational levels mediated by stress-associated molecules and metabolites, including phytohormones. We conclude by emphasizing how unravelling the molecular circuitry underlying diverse priming-stimuli-induced stress responses could propel the use of priming as a management practice for crop plants. This practice, in combination with precision agriculture, could aid in increasing yield quantity and quality to meet the rapidly rising demand for food.

    

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