PSK signaling controls ABA homeostasis and promotes shoot growth under mannitol stress

We hypothesized that the growth-promoting activity of the peptide hormone phytosulfokine (PSK), may be important to maintain growth under abiotic stress. To test this hypothesis, we employed mannitol as a stressor and analyzed the involvement of abscisic acid (ABA) that mediates a subset of mannitol responses. Inhibition of seed germination by ABA or mannitol was independent of PSK receptor signaling whereas repression of cotyledon greening was partially dependent on PSKR signaling with receptor null pskr1-3 pskr2-1 seedlings showing enhanced greening. Mannitol led to dose-dependent shoot growth inhibition that was alleviated by PSKR signaling. With mannitol, pskr1-3 pskr2-1 seedlings had strongly reduced shoot fresh and dry weights incompared to wild type. Analysis of pskr1-3 and pskr2-1 single receptor loss-of-function lines revealed that signaling via PSKR1 is crucial for shoot growth promotion under mannitol stress. Mannitol and ABA induced expression of PSK3 and PSKR1 and ABA promoted expression of PSK2 and PSK4. In turn, PSKR signaling was required for mannitol-induced accumulation of ABA in the shoot revealing a regulatory feedback loop. PSKRs repressed expression of UGT71B6 encoding an ABA UDP-glucosyltransferase and maintained expression of BG1, an ABA glucosidase which may lead to reduced ABA-glucose conjugation and enhanced ABA remobilization. Marker gene expression analyses supported the conclusion that PSKR and mannitol signaling pathways crosstalk, a conclusion that was supported by the observation that PSK receptor signaling enhanced sensitivity to ABA in mannitol-stressed shoots. In conclusion, PSKR signaling maintains shoot growth under mannitol stress in part by interfering with the ABA pathway.One-sentence summaryPSK receptor signaling is required to delay cotyledon greening in response to mannitol and ABA nad it promotes shoot growth under mannitol stress by controlling ABA levels and ABA responsiveness.

Friendly regulates membrane depolarization induced mitophagy in Arabidopsis

The oxidative environment within the mitochondria makes them particularly vulnerable to proteotoxic stress. To maintain a healthy mitochondrial network, eukaryotes have evolved multi-tiered quality control pathways. If the stress cannot be alleviated, defective mitochondria are selectively removed by autophagy via a process termed mitophagy. Despite significant advances in metazoans and yeast, in plants, the molecular underpinnings of mitophagy are largely unknown. Here, using time-lapse imaging, electron tomography and biochemical assays, we show that uncoupler treatments cause loss of mitochondrial membrane potential and induce autophagy in Arabidopsis. The damaged mitochondria are selectively engulfed by autophagosomes that are ATG5 dependent and labelled by ATG8 proteins. Friendly, a member of the Clustered Mitochondria protein family, is recruited to the damaged mitochondria to mediate mitophagy. In addition to stress, mitophagy is also induced during de-etiolation, a major cellular transformation during photomorphogenesis that involves chloroplast biogenesis. De-etiolation triggered mitophagy regulates cotyledon greening, pointing towards an inter-organellar cross-talk mechanism. Altogether our results demonstrate how plants employ mitophagy to recycle damaged mitochondria during stress and development.

VlbZIP30 of grapevine functions in drought tolerance via the abscisic acid core signaling pathway

Drought stress limits the growth and development of grapevines, thereby reducing productivity, but the mechanisms by which grapevines respond to drought stress remain largely uncharacterized. Here, we characterized a group A bZIP gene from ‘Kyoho’ grapevine, VlbZIP30, which was shown to be induced by abscisic acid (ABA) and dehydration stress. Overexpression of VlbZIP30 in transgenic Arabidopsis enhanced dehydration tolerance during seed germination, and in the seedling and adult stages. Transcriptome analysis revealed that a major proportion of ABA- and/or drought-responsive genes are transcriptionally regulated by VlbZIP30 during ABA or mannitol treatment at the cotyledon greening stage. We identified an A. thaliana G-box motif (CACGTG) and a potential grapevine G-box motif (MCACGTGK) in the promoters of the 39 selected A. thaliana genes up-regulated in the transgenic plants and in the 35 grapevine homologs, respectively. Subsequently, using two grapevine-related databases, we found that 74% and 84% (a total of 27 genes) of the detected grapevine genes were significantly up-regulated by ABA and drought stress, respectively, suggesting that these 27 genes involve in ABA or dehydration stress and may be regulated by VlbZIP30 in grapevine. We propose that VlbZIP30 functions as a positive regulator of drought-responsive signaling in the ABA core signaling pathway.HighlightVlbZIP30 positively regulate plant drought tolerance through regulated the expression of 27 grapevine candidate genes via G-box cis-element (MCACGTGK) in ABA signaling pathway.

Characterization of globoids and iron-rich particles in cotyledons of Pinusbanksiana seeds and seedlings

The cotyledons of Pinusbanksiana Lamb, from dry seeds and seedlings were studied for differences in the elements present in globoids. Globoids are mineral nutrient storage bodies. Parallel studies were conducted on iron-rich particles. A comparison of globoids from cotyledons of dry seeds with those of seedlings found that P, K, and Mg levels declined markedly, while Ca, Fe, Zn, and Mn levels increased significantly. A comparison of iron-rich particles showed that levels of P, K, Mg, and Ca changed, while Fe, Zn, and Mn remained unchanged. The iron-rich particles persisted during cotyledon greening and were definitely located in chloroplasts. This is the first report of such particles in chloroplasts of conifers.