Heat-stress induced expression of stress-inducible nucleotide exchange factor Fes1 in seagrass Zostera japonica

Global transcriptome dynamics of seagrass flowering and seed development process: insights from the iconic seagrass Zostera marina L

Seagrasses are the only group of higher angiosperms capable of fully living in seawater, playing a significant role in plant evolutionary history. However, studies on the molecular regulatory networks underlying sexual reproduction in seagrasses remain limited. This study evaluated the morphological changes of the spathe during eelgrass sexual reproduction and analyzed global transcriptome dynamics across eight sequential stages. The key findings are as follows:(1) Key flowering integrators such as FT, SOC1, AP1, and LFY exhibited high expression levels during the early stages, indicating their involvement in the induction of eelgrass flowering, consistent with terrestrial plants. (2) Based on the classical model of floral organ development in terrestrial plants - the "ABCDE model, genes related to the development of stamens, carpels, and ovules of eelgrass, including B-, C-, D-, and E-class genes, were identified. (3) Photosynthesis was temporarily suppressed after the initiation of sexual reproduction, and gradually resumed during the seed development stage, suggesting that the developed seed may perform photosynthesis. The Fv/Fm value (0.641 ± 0.028) of seeds at the developed seed stage further indicated that these seeds are indeed capable of photosynthesis. These findings provide important insights into the potential mechanisms underlying seagrass sexual reproduction and enrich knowledge of its reproductive genetics.

Endoplasmic stress sensor Ire1 is involved in cytosolic/nuclear protein quality control in Pichia pastoris cells independent of HAC1

In eukaryotic species, dysfunction of the endoplasmic reticulum (ER), namely, ER stress, provokes a cytoprotective transcription program called the unfolded protein response (UPR). The UPR is triggered by transmembrane ER-stress sensors, including Ire1, which acts as an endoribonuclease to splice and mature the mRNA encoding the transcription factor Hac1 in many fungal species. Through analyses of the methylotrophic yeast Pichia pastoris (syn. Komagataella phaffii), we revealed a previously unknown function of Ire1. In P. pastoris cells, the IRE1 knockout mutation (ire1Δ) and HAC1 knockout mutation (hac1Δ) caused only partially overlapping gene expression changes. Protein aggregation and the heat shock response (HSR) were induced in ire1Δ cells but not in hac1Δ cells even under non-stress conditions. Moreover, Ire1 was further activated upon high-temperature culturing and conferred heat stress resistance to P. pastoris cells. Our findings cumulatively demonstrate an intriguing case in which the UPR machinery controls cytosolic protein folding status and the HSR, which is known to be activated upon the accumulation of unfolded proteins in the cytosol and/or nuclei.

Cloning and activity analysis of the promoter of nucleotide exchange factor gene ZjFes1 from the seagrasses Zostera japonica

After HSP70 binds to the J domain of the substrate and co-chaperone protein, ATP is hydrolyzed to ADP, and the nucleotide exchange factors (NEFs) promote the release of ADP. Under physiological conditions, the nucleotide exchange step is the rate-limiting step, which is accelerated by NEFs. In this study, the promoter of nucleotide exchange factor ZjFes1 was cloned, and its expression in tissues and under heat stress was studied to understand the regulatory mechanism of ZjFes1 and provide the molecular basis to study heat tolerance mechanism of seagrass. It was found that the promoter has common cis-acting elements in promoter and enhancer regions CAAT-box, as well as light response elements AE-box, Box 4 and TCCC-motif, a cis-acting regulatory element essential for the anaerobic induction of ARE, hormone response elements CGTCA-motif and TGACG-motif (MeJA response element), GARE-motif (gibberellin response element), TGA-element (auxin response element), a cis-acting regulatory element related to meristem expression CAT-box, and a cis-acting element involved in defense and stress responsiveness of TC-rich repeats. Two-week-old seedlings exhibited weak GUS activities in their cotyledons. In addition, the AtFes1A promoter was constitutively active in the anthers. After exposure to 38 °C for 2 h, the root tips of two-week-old seedlings were stained a strong blue. Heat-inducible activities of GUS were also observed in the cotyledons, roots, leaves, anthers, sepals and siliques.