The Mechanistic Underpinnings of anago1-Mediated, Environmentally Dependent, and Stochastic Phenotype  

Abstract

98195-5065 (G.A.M., T.L., C.Q.)The crucial role of microRNAs in plant development is exceedingly well supported; their importance in environmental robustness is studied in less detail. Here, we describe a novel, environmentally dependent phenotype in hypomorphic argonaute1 (ago1) mutants and uncover its mechanistic underpinnings in Arabidopsis (Arabidopsis thaliana). AGO1 is a key player in microRNA-mediated gene regulation. We observed transparent lesions on embryonic leaves of ago1 mutant seedlings. These lesions increased in frequency in full-spectrum light. Notably, the lesion phenotype was most environmentally responsive in ago1-27 mutants. This allele is thought to primarily affect translational repression, which has been linked with the response to environmental perturbation. Using several lines of evidence, we found that these lesions represent dead and dying tissues due to an aberrant hypersensitive response. Although all three canonical defense hormone pathways (salicylic acid, jasmonate, and jasmonate/ethylene pathways) were up-regulated in ago1 mutants, we demonstrate that jasmonate perception drives the lesion phenotype. Double mutants of ago1 and coronatine insensitive1, the jasmonate receptor, showed greatly decreased frequency of affected seedlings. The chaperone HEAT SHOCK PROTEIN 90 (HSP90), which maintains phenotypic robustness in the face of environmental perturbations, is known to facilitate AGO1 function. HSP90 perturbation has been shown previously to upregulate jasmonate signaling and to increase plant resistance to herbivory. Although single HSP90 mutants showed subtly elevated levels of lesions, double mutant analysis disagreed with a simple epistatic model for HSP90 and AGO1 interaction; rather, both appeared to act nonadditively in producing lesions. In summary, our study identifies AGO1 as a major, largely HSP90-independent, factor in providing environmental robustness to plants. ARGONAUTE1 (AGO1) is an ancient, highly conserved essential protein. One of 10 functionally distinct AGO proteins in the plant Arabidopsis (Arabidopsis thaliana), AGO1 uses microRNAs (miRNAs) to decrease the expression of target genes. AGO1 and the miRNA pathway are crucial for many regulatory processes throughout development and in response to environmental stimuli. As frequent components of feedforward loops, miRNAs also play important roles in controlling gene expression noise and maintaining the phenotypic robustness of specific traits in several organisms, including plants ( Lempe et al., 2013).AGO1 and miRNAs also are critical for proper plant responses to abiotic stress. The expression levels of miRNAs respond to heat shock, cold, drought, oxidative stress, UV light exposure, and hypoxia (Sunkar et al., 2012). For example, in response to drought, the expression of miR169 decreases and the expression of its target gene, encoding the transcription factor NFYA5, increases in Arabidopsis (Li et al., 2008). Increased expression of NFYA5 supports plant survival in drought conditions. Transgenic plants ove...

HSP90 buffers newly induced mutations in massively mutated plant lines

“…This HSP90-dependent increase in phenotype frequencies agrees with several previous studies (29,30,34,36,56). We also found two GM lines with a significantly decreased frequency of the aberrant phenotype (Figure 4C, GM dark blue lines, Fisher's exact test: p-adj<0.05, OR<0.03), reminiscent of previous findings that HSP90 perturbation can conceal the phenotypic consequences of underlying variation (26,28,32,41).…”

“…Only two DM M 2 plants with deformed aerial organs showed additional defects; both produced M 3 offspring with these defects; none were HSP90-responsive. In stark contrast, 19 GM M 2 showed additional aberrant phenotypes; 16 of these produced M 3 offspring with these defects; (29,56), upon HSP90-perturbation, unmutagenized Col-0 wildtype plants tended to show dwarf phenotypes, lesions on cotyledons, discoloration, and epinastic organs among others. Second, about half of the mutagenized M 3 also showed these phenotypes in response to HSP90 perturbation, albeit often at far higher frequency.…”

“…We devised a mutant scoring index to estimate frequency of mutant-like phenotypes quickly and objectively after mutagenesis. We based this index on known HSP90-responsive phenotypes, such as size-related traits or lesions on aerial tissue (29,42,56). In this index, 16…”

Characterization and Identification of a woody lesion mimic mutant lmd, showing defence response and resistance to Alternaria alternate in birch

“…Some environmental factors such as light 53 , 54 , temperature, and humidity 55 , 56 can influence the phenotype of LMM 57 . Both light and temperature influence the chloroplast number and morphology in the FZL mutant 58 .…”

Osmotic Stress Induced Cell Death in Wheat Is Alleviated by Tauroursodeoxycholic Acid and Involves Endoplasmic Reticulum Stress–Related Gene Expression

“…We used trypan blue staining to visually detect cell death according to Mason et al ( 2016 ). To do this, leaf segments were stained in a test tube containing 0.04% lactophenol-trypan blue solution (Sigma-Aldrich, USA) dissolved in 10 mL of distilled water and diluted 1:1 with ethanol.…”