Understanding the precise regulatory mechanisms of plant development and stress responses at the post-translational level is currently a topic of intensive research. Protein ubiquitination, including the sequential performances of ubiquitin-activating (E1), ubiquitin-conjugating (E2) and ubiquitin ligase (E3) enzymes, is a refined post-translational modification ubiquitous in all eukaryotes. Plants are an integral part of our ecosystem and, as sessile organisms, the ability to perceive internal and external signals and to adapt well to various environmental challenges is crucial for their survival. Over recent decades, extensive studies have demonstrated that protein ubiquitination plays key roles in multiple plant developmental stages (e.g. seed dormancy and germination, root growth, flowering time control, self-incompatibility and chloroplast development) and several abiotic stress responses (e.g. drought and high salinity), by regulating the abundance, activities or subcellular localizations of a variety of regulatory polypeptides and enzymes. Importantly, diverse E3 ligases are involved in these regulatory pathways by mediating phytohormone and light signaling or other pathways. In this updated review, we mainly summarize recent advances in our understanding of the regulatory roles of protein ubiquitination in plant development and plant–environment interactions, and primarily focus on different types of E3 ligases because they play critical roles in determining substrate specificity.

In intercropping systems shading conditions significantly impair the seed yield and quality of soybean, and rarely someone investigated the minimum amount of light requirement for soybean growth and development. Therefore, it is an urgent need to determine the threshold light intensity to ensure sustainable soybean production under these systems. An integrated approach combining morphology, physiology, biochemistry and genetic analysis was undertaken to study the light intensity effects on soybean growth and development. A pot experiment was set up in a growth chamber under increasing light intensity treatments of 100 (L₁₀₀), 200 (L₂₀₀), 300 (L₃₀₀), 400 (L₄₀₀), and 500 (L₅₀₀) μmol m⁻² s⁻¹. Compared with L₁₀₀, plant height, hypocotyl length, and abaxial leaf petiole angle were decreased, biomass, root:shoot ratio, and stem diameter were increased, extremum was almost observed in L₄₀₀ and L_500. Leaf petiole movement and leaf hyponasty in each treatment has presented a tendency to decrease the leaf angle from L₅₀₀ to L₁₀₀. In addition, the cytochrome content (Chl a, Chl b, Car), net photosynthetic rate, chlorophyll fluorescence values of F_v/F_m, $F_{\text{v}}{}^{\prime }$/$F_{\text{m}}{}^{\prime }$, ETR, Φ_PSII, and qP were increased as the light intensity increased, and higher values were noted under L₄₀₀. Leaf microstructure and chloroplast ultrastructure positively improved with increasing light intensity, and leaf-thickness, palisade, and spongy tissues-thickness were increased by 105, 90, and 370%, under L₅₀₀ than L₁₀₀. Moreover, the cross-sectional area of chloroplast (C) outer membrane and starch grains (S), and sectional area ratio (S:C) was highest under L₄₀₀ and L₅₀₀, respectively. Compared to L₁₀₀, the content of starch granules increased by 35.5, 122.0, 157.6, and 145.5%, respectively in L₄₀₀. The same trends were observed in the enzyme activity of sucrose-synthase, sucrose phosphate synthase, starch synthase, rubisco, phosphoenol pyruvate carboxykinase, and phosphoenol pyruvate phosphatase. Furthermore, sucrose synthesis-related genes were also up-regulated by increasing light intensity, and the highest seed yield and yield related parameters were recorded in the L₄₀₀. Overall, these results suggested that 400 and 500 μmol m⁻² s⁻¹ is the optimum light intensity which positively changed the leaf orientation and adjusts leaf angle to perpendicular to coming light, consequently, soybean plants grow well under prevailing conditions.

Phytohormones regulate numerous important biological processes in plant development and biotic/abiotic stress response cascades. More than 50 and 100 years have passed since the initial discoveries of the phytohormones abscisic acid (ABA) and gibberellins (GA), respectively. Over the past several decades, numerous elegant studies have demonstrated that ABA and GA antagonistically regulate many plant developmental processes, including seed maturation, seed dormancy and germination, root initiation, hypocotyl and stem elongation, and floral transition. Furthermore, as a well-established stress hormone, ABA plays a key role in plant responses to abiotic stresses, such as drought, flooding, salinity and low temperature. Interestingly, recent evidence revealed that GA are also involved in plant response to adverse environmental conditions. Consequently, the complex crosstalk networks between ABA and GA, mediated by diverse key regulators, have been extensively investigated and documented. In this updated mini-review, we summarize the most recent advances in our understanding of the antagonistically regulatory roles of ABA and GA in different stages of plant development and in various plant-environment interactions, focusing on the crosstalk between ABA and GA at the levels of phytohormone metabolism and signal transduction.

Auxin is an important phytohormone which mediates diverse development processes in plants. Published research has demonstrated that auxin induces seed dormancy. However, the precise mechanisms underlying the effect of auxin on seed germination need further investigation, especially the relationship between auxins and both abscisic acid (ABA) and gibberellins (GAs), the latter two phytohormones being the key regulators of seed germination. Here we report that exogenous auxin treatment represses soybean seed germination by enhancing ABA biosynthesis, while impairing GA biogenesis, and finally decreasing GA₁/ABA and GA₄/ABA ratios. Microscope observation showed that auxin treatment delayed rupture of the soybean seed coat and radicle protrusion. qPCR assay revealed that transcription of the genes involved in ABA biosynthetic pathway was up-regulated by application of auxin, while expression of genes involved in GA biosynthetic pathway was down-regulated. Accordingly, further phytohormone quantification shows that auxin significantly increased ABA content, whereas the active GA₁ and GA₄ levels were decreased, resulting insignificant decreases in the ratiosGA₁/ABA and GA₄/ABA.Consistent with this, ABA biosynthesis inhibitor fluridone reversed the delayed-germination phenotype associated with auxin treatment, while paclobutrazol, a GA biosynthesis inhibitor, inhibited soybean seed germination. Altogether, exogenous auxin represses soybean seed germination by mediating ABA and GA biosynthesis.