NUA and ESD4 negatively regulate ABA signaling during seed germination

SIZ1 SUMOylates and stabilizes WRI1 to safeguard seed filling and fatty acid biosynthesis under high-temperature stress

High-temperature stress hinders seed filling, reducing seed quality and crop yield. However, the molecular mechanisms underlying this process remain unclear. Here, we identify SAP AND MIZ1 DOMAIN-CONTAINING LIGASE1 (SIZ1) as a key regulator of seed filling under prolonged high temperatures in Arabidopsis (Arabidopsis thaliana). SIZ1 and WRINKLED1 (WRI1) are co-expressed during seed filling, and overexpressing either gene enhances seed filling and promotes fatty acid biosynthesis under high-temperature stress. Genetic and biochemical analyses revealed that SIZ1 stabilizes WRI1 by promoting its SUMOylation at Lys-257 and Lys-266, thereby inhibiting its interaction with the CULLIN3-based ubiquitin E3 ligase adaptor protein BTB/POZMATH (BPM) and preventing its ubiquitination and degradation. Mutating these SUMOylation sites accelerates WRI1 degradation, impairing its function in seed filling under high-temperature stress. Furthermore, high-temperature stress induces SIZ1 expression and reduces WRI1 levels, suggesting that SIZ1-mediated SUMOylation counteracts high-temperature stress-induced WRI1 instability. These findings establish SIZ1 as a crucial factor in maintaining WRI1 stability and seed filling under high-temperature stress, providing valuable genetic resources and a theoretical foundation for addressing prolonged high-temperature stress in agricultural production.

SnRK2s: Kinases or Substrates?

Throughout their life cycle, plants persistent through environmental adversities that activate sophisticated stress-signaling networks, with protein kinases serving as pivotal regulators of these responses. The sucrose non-fermenting-1-related protein kinase 2 (SnRK2), a plant-specific serine/threonine kinase, orchestrates stress adaptation by phosphorylating downstream targets to modulate gene expression and physiological adjustments. While SnRK2 substrates have been extensively identified, the existing literature lacks a systematic classification of these components and their functional implications. This review synthesizes recent advances in characterizing SnRK2-phosphorylated substrates in Arabidopsis thaliana, providing a mechanistic framework for their roles in stress signaling and developmental regulation. Furthermore, we explore the understudied paradigm of SnRK2 undergoing multilayered post-translational modifications (PTMs), including phosphorylation, ubiquitination, SUMOylation, S-nitrosylation, sulfation (S-sulfination and tyrosine sulfation), and N-glycosylation. These PTMs collectively fine-tune SnRK2 stability, activity, and subcellular dynamics, revealing an intricate feedback system that balances kinase activation and attenuation. By integrating substrate networks with regulatory modifications, this work highlights SnRK2's dual role as both a phosphorylation executor and a PTM-regulated scaffold, offering new perspectives for engineering stress-resilient crops through targeted manipulation of SnRK2 signaling modules.

Allelic variation of TaABI5-A4 significantly affects seed dormancy in bread wheat

KEY MESSAGE

We identified a pivotal transcription factor TaABI5-A4 that is significantly associated with pre-harvest sprouting in wheat; its function in regulating seed dormancy was confirmed in transgenic rice. ABI5 is a critical transcription factor in regulation of crop seed maturation, dormancy, germination, and post-germination. Sixteen copies of homologous sequences of ABI5 were identified in Chinese wheat line Zhou 8425B. Cultivars of two haplotypes TaABI5-A4a and TaABI5-A4b showed significantly different seed dormancies. Based on two SNPs between the sequences of TaABI5-A4a and TaABI5-A4b, two complementary dominant sequence-tagged site (STS) markers were developed and validated in a natural population of 103 Chinese wheat cultivars and advanced lines and 200 recombinant inbred lines (RILs) derived from the Yangxiaomai/Zhongyou 9507 cross; the STS markers can be used efficiently and reliably to evaluate the dormancy of wheat seeds. The transcription level of TaABI5-A4b was significantly increased in TaABI5-A4a-GFP transgenic rice lines compared with that in TaABI5-A4b-GFP. The average seed germination index of TaABI5-A4a-GFP transgenic rice lines was significantly lower than those of TaABI5-A4b-GFP. In addition, seeds of TaABI5-A4a-GFP transgenic lines had higher ABA sensitivity and endogenous ABA content, lower endogenous GA content and plant height, and thicker stem internodes than those of TaABI5-A4b-GFP. Allelic variation of TaABI5-A4-affected wheat seed dormancy and the gene function was confirmed in transgenic rice. The transgenic rice lines of TaABI5-A4a and TaABI5-A4b had significantly different sensitivities to ABA and contents of endogenous ABA and GA in mature seeds, thereby influencing the seed dormancy, plant height, and stem internode length and diameter.

Pepper SUMO protease CaDeSI2 positively modulates the drought responses via deSUMOylation of clade A PP2C CaAITP1

Posttranslational modification of multiple ABA signaling components is an essential process for the adaptation and survival of plants under stress conditions. In our previous study, we established that the pepper group A PP2C protein CaAITP1, one of the core components of ABA signaling, undergoes ubiquitination mediated by the RING-type E3 ligase CaAIRE1. In this study, we discovered an additional form of regulation mediated via the SUMOylation of CaAITP1. Pepper plants subjected to drought stress were characterized by reductions in both the stability and SUMOylation of CaAITP1 protein. Moreover, we identified a SUMO protease, Capsicum annuum DeSUMOylating Isopeptidase 2 (CaDeSI2), as a new interacting partner of CaAITP1. In vitro and in vivo analyses revealed that CaAITP1 is deSUMOylated by CaDeSI2. Silencing of CaDeSI2 in pepper plants led to drought-hypersensitive and ABA-hyposensitive phenotypes, whereas overexpression of CaDeSI2 in transgenic Arabidopsis plants resulted in the opposite phenotypes. Importantly, we found that the CaAITP1 protein was stabilized in response to the silencing of CaDeSI2, and CaDeSI2 and CaAITP1 co-silenced pepper plants were characterized by drought-tolerant phenotypes similar to those observed in CaAITP1-silenced pepper. Collectively, our findings indicate that CaDeSI2 reduces the stability of CaAITP1 via deSUMOylation, thereby positively regulating drought tolerance.