The Arabidopsis CORI3 promoter contains two cis-acting regulatory regions required for transcriptional activity in companion cells

Ubiquitome profiling reveals a regulatory pattern of UPL3 with UBP12 on metabolic-leaf senescence

The HECT-type UPL3 ligase plays critical roles in plant development and stress protection, but understanding of its regulation remains limited. Here, the multi-omics analyses of ubiquitinated proteins in <i>upl3</i> mutants were performed. A landscape of UPL3-dependent ubiquitinated proteins is constructed: Preferential ubiquitination of proteins related to carbon fixation represented the largest set of proteins with increased ubiquitination in the <i>upl3</i> plant, including most of carbohydrate metabolic enzymes, BRM, and variant histone, whereas a small set of proteins with reduced ubiquitination caused by the <i>upl3</i> mutation were linked to cysteine/methionine synthesis, as well as hexokinase 1 (HXK1) and phosphoenolpyruvate carboxylase 2 (PPC2). Notably, ubiquitin hydrolase 12 (UBP12), BRM, HXK1, and PPC2 were identified as the UPL3-interacting partners in vivo and in vitro. Characterization of <i>brm</i>, <i>upl3</i>, <i>ppc2</i>, <i>gin2</i>, and <i>ubp12</i> mutant plants and proteomic and transcriptomic analysis suggested that UPL3 fine-tunes carbohydrate metabolism, mediating cellular senescence by interacting with UBP12, BRM, HXK1, and PPC2. Our results highlight a regulatory pattern of UPL3 with UBP12 as a hub of regulator on proteolysis-independent regulation and proteolysis-dependent degradation.

Companion cells: a diamond in the rough

Vascular plants have developed highly specialized cells to transport nutrients and developmental signals. The differentiation process includes the degradation of multiple organelles of the sieve element cells (SEs) to facilitate transport and, as a consequence, SEs become dependent on neighboring companion cells (CCs). Despite its importance for phloem function and flowering time control, CCs are still a mysterious cell type. In this review, we gather all the genes known to be expressed in CCs, in different organs and organisms, with the objective of better understanding CC identity and function.

Cloning and functional characterization of the promoter of PsSEOF1 gene from Pisum sativum under different stress conditions using Agrobacterium-mediated transient assay

PsSEOF1, a SEO (sieve element occlusion) gene family protein (forisome) is calcium powered motor protein and is located close to plasma membrane of sieve element. In sieve element (SE) it senses the calcium ion levels and undergoes ATP-independent conformational shifts. Forisome, meaning gate-bodies (Latin foris: wing of a gate; Greek soma: body). Recent reports show that SEO gene family protein can prevent the loss of nutrient rich photoassimilate upon wound injury. The regulation of SEO protein forisome under abiotic/ biotic stress is still unknown. The analysis of cis-regulatory element present in the upstream region is not well understood. Tissue specific promoters guarantee correct expression when it perceives particular stimuli. Here we report isolation of tissue specific promoter of PsSEOF1 was isolated by gene walking PCR from P. sativum (pea) genomic DNA library constructed by BD genome walker kit. In silico analysis revealed several putative cis element within this promoter sequence like wound response, cold, dehydration. Putative elements which might be required for its vascular tissue specificity has also been identified. The GUS activities of PsSEOF1 promoter-GUS chimeric construct in the agroinfiltrated leaves under different environmental stress abiotic and biotic like wound, cold, salt and phytohormones has shown high level of GUS activity. To identify the activity of PsSEOF1 promoter under different stress condition an Agrobacterium-mediated transient expression of tobacco plants were subjected to histochemical GUS staining. Stress-inducible nature of PsSEOF1 promoter opens possibility for the study of the PsSEOF1 gene regulation under stress condition. The isolated promoter sequence could serve as an important candidate for tissue specific promoter in genetic engineering of plant under stress conditions.

Wheat chloroplast targeted sHSP26 promoter confers heat and abiotic stress inducible expression in transgenic Arabidopsis Plants

The small heat shock proteins (sHSPs) have been found to play a critical role in physiological stress conditions in protecting proteins from irreversible aggregation. To characterize the hloroplast targeted sHSP26 promoter in detail, deletion analysis of the promoter is carried out and analysed via transgenics in Arabidopsis. In the present study, complete assessment of the importance of CCAAT-box elements along with Heat shock elements (HSEs) in the promoter of sHSP26 was performed. Moreover, the importance of 5' untranslated region (UTR) has also been established in the promoter via Arabidopsis transgenics. An intense GUS expression was observed after heat stress in the transgenics harbouring a full-length promoter, confirming the heat-stress inducibility of the promoter. Transgenic plants without UTR showed reduced GUS expression when compared to transgenic plants with UTR as was confirmed at the RNA and protein levels by qRT-PCR and GUS histochemical assays, thus suggesting the possible involvement of some regulatory elements present in the UTR in heat-stress inducibility of the promoter. Promoter activity was also checked under different abiotic stresses and revealed differential expression in different deletion constructs. Promoter analysis based on histochemical assay, real-time qPCR and fluorimetric analysis revealed that HSEs alone could not transcribe GUS gene significantly in sHSP26 promoter and CCAAT box elements contribute synergistically to the transcription. Our results also provide insight into the importance of 5`UTR of sHsp26 promoter thus emphasizing the probable role of imperfect CCAAT-box element or some novel cis-element with respect to heat stress.

Multiple cis-regulatory elements are involved in the complex regulation of the sieve element-specific MtSEO-F1 promoter from Medicago truncatula

The sieve element occlusion (SEO) gene family includes several members that are expressed specifically in immature sieve elements (SEs) in the developing phloem of dicotyledonous plants. To determine how this restricted expression profile is achieved, we analysed the SE-specific Medicago truncatula SEO-F1 promoter (PMtSEO-F1) by constructing deletion, substitution and hybrid constructs and testing them in transgenic tobacco plants using green fluorescent protein as a reporter. This revealed four promoter regions, each containing cis-regulatory elements that activate transcription in SEs. One of these segments also contained sufficient information to suppress PMtSEO-F1 transcription in the phloem companion cells (CCs). Subsequent in silico analysis revealed several candidate cis-regulatory elements that PMtSEO-F1 shares with other SEO promoters. These putative sieve element boxes (PSE boxes) are promising candidates for cis-regulatory elements controlling the SE-specific expression of PMtSEO-F1.