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Pseudogamous apomixis in Paspalum simplex generates seeds with embryos genetically identical to the mother plant and endosperms deviating from the canonical 2(maternal):1(paternal) parental genome contribution into a maternal excess 4m:1p genome ratio. In P. simplex, the gene homologous to that coding for subunit 3 of the ORIGIN OF RECOGNITION COMPLEX (PsORC3) exists in three isogenic forms: PsORC3a is apomixis specific and constitutively expressed in developing endosperm whereas PsORCb and PsORCc are up-regulated in sexual endosperms and silenced in apomictic ones. This raises the question of how the different arrangement and expression profiles of these three ORC3 isogenes are linked to seed development in interploidy crosses generating maternal excess endosperms. We demonstrate that down-regulation of PsORC3b in sexual tetraploid plants is sufficient to restore seed fertility in interploidy 4n×2n crosses and, in turn, its expression level at the transition from proliferating to endoreduplication endosperm developmental stages dictates the fate of these seeds. Furthermore, we show that only when being maternally inherited can PsORC3c up-regulate PsORC3b. Our findings lay the basis for an innovative route-based on ORC3 manipulation-to introgress the apomictic trait into sexual crops and overcome the fertilization barriers in interploidy crosses., (© The Author(s) 2023. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

The discovery that much of the extracellular proteome in eukaryotic cells consists of proteins lacking a signal peptide, which cannot therefore enter the secretory pathway, has led to the identification of alternative protein secretion routes bypassing the Golgi apparatus. However, proteins harboring a signal peptide for translocation into the endoplasmic reticulum can also be transported along these alternative routes, which are still far from being well elucidated in terms of the molecular machineries and subcellular/intermediate compartments involved. In this review, we first try to provide a definition of all the unconventional protein secretion pathways in eukaryotic cells, as those pathways followed by proteins directed to an 'external space' bypassing the Golgi, where 'external space' refers to the extracellular space plus the lumen of the secretory route compartments and the inner space of mitochondria and plastids. Then, we discuss the role of the endoplasmic reticulum in sorting proteins toward unconventional traffic pathways in plants. In this regard, various unconventional pathways exporting proteins from the endoplasmic reticulum to the vacuole, plasma membrane, apoplast, mitochondria, and plastids are described, including the short routes followed by the proteins resident in the endoplasmic reticulum., (© The Author(s) 2017. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

HMGB1 is a nuclear protein that signals tissue damage, as it is released by cells dying traumatically or secreted by activated innate immunity cells. Extracellular HMGB1 elicits the migration to the site of tissue damage of several cell types, including inflammatory cells and stem cells. The identity of the signaling pathways activated by extracellular HMGB1 is not known completely: We reported previously that ERK and NF-kappaB pathways are involved, and we report here that Src is also activated. The ablation of Src or inhibition with the kinase inhibitor PP2 blocks migration toward HMGB1. Src associates to and mediates the phosphorylation of FAK and the formation of focal adhesions.

Protein bodies (PB) are stable polymers naturally formed by certain seed storage proteins within the endoplasmic reticulum (ER). The human immunodeficiency virus negative factor (Nef) protein, a potential antigen for the development of an anti-viral vaccine, is highly unstable when introduced into the plant secretory pathway, probably because of folding defects in the ER environment. The aim of this study was to promote the formation of Nef-containing PB in tobacco (Nicotiana tabacum) leaves by fusing the Nef sequence to the N-terminal domains of the maize storage protein gamma-zein or to the chimeric protein zeolin (which efficiently forms PB and is composed of the vacuolar storage protein phaseolin fused to the N-terminal domains of gamma-zein). Protein blots and pulse-chase indicate that fusions between Nef and the same gamma-zein domains present in zeolin are degraded by ER quality control. Consistently, a mutated zeolin, in which wild-type phaseolin was substituted with a defective version known to be degraded by ER quality control, is unstable in plant cells. Fusion of Nef to the entire zeolin sequence instead allows the formation of PB detectable by electron microscopy and subcellular fractionation, leading to zeolin-Nef accumulation higher than 1% of total soluble protein, consistently reproduced in independent transgenic plants. It is concluded that zeolin, but not its gamma-zein portion, has a positive dominant effect over ER quality control degradation. These results provide insights into the requirements for PB formation and avoidance of quality-control degradation, and indicate a strategy for enhancing foreign protein accumulation in plants.

Zeins, the main storage proteins of maize that accumulate in the endoplasmic reticulum of the endosperm cells, are particularly interesting because they are rich in the essential sulphur amino acids. Overexpression of certain zein genes in plants such as alfalfa would be expected to improve the nutritional characteristics of this crop. Recently, significant accumulation values have been reached, but still far from those considered useful for nutritional purposes. This study investigates whether targeting to compartments other than the endoplasmic reticulum (cytosol and chloroplasts) could result in increasing beta-zein accumulation in transgenic plants. To address beta-zein to the cytosol, the fragment which codes for the signal peptide has been removed. beta-zein has also been targeted to alfalfa and tobacco chloroplasts by a transit peptide signal. Both tobacco, as a model plant species, and alfalfa have been transformed with the assembled constructs. An alternative route to accumulate beta-zein in the chloroplasts is to synthesize beta-zein directly in the plastid lumen. Thus, the beta-zein gene has also been inserted into tobacco plastid DNA. The beta-zein gene in each different type of transformed plant was properly transcribed, as determined by northern blot analysis, but no accumulation of beta-zein was detected, either in the cytoplasm or in the chloroplasts of alfalfa and tobacco transformed plants. Therefore, it is concluded that chloroplasts and the cytosol are not favourable subcellular locations for zein protein accumulation.