The interaction of plant biotic and abiotic stresses: from genes to the field

Belowground inter-ramet water transport capacity in Populus euphratica, a Central Asian desert phreatophyte

Populus euphratica Oliv. is a widespread phreatophytic tree species that forms riparian forests in (hyper-)arid regions of Central Asia. Its recruitment strongly relies on vegetative propagation from 'root suckers' that emerge from underground root spacers. The water transport through the spacers, although decisive for emerging ramets, has only rarely been quantified, but is crucial for the vegetative regeneration of the forests. In root spacers with different diameters collected from a mature poplar forest in northwest China, we calculated the hydraulic conductivity (k_c ) from anatomical investigations on the basis of a modified Hagen-Poiseuille equation and measured it (k_m ) with a perfusion solution in the laboratory. The k_m values were compared with the water use by young and mature P. euphratica trees determined in previous studies. We obtained a significant correlation between k_m and k_c (which, however, was higher by at least one order of magnitude). Due to the extensive occurrence of tyloses, particularly in older conduits and thicker spacers, and because the conduit area did not increase with spacer diameter, neither k_c nor k_m increased with an increase in spacer diameter. The water supply through the spacers would be sufficient to meet the water demand even of mature trees. Our results provide a mechanistic explanation for the observed occurrence of P. euphratica clones across large areas and, provided that they are also valid for stands with larger distances to the water table, for the sustained growth and vegetative reproduction of P. euphratica stands growing at larger distances from the groundwater.

Phenotypic analysis combined with tandem mass tags (TMT) labeling reveal the heterogeneity of strawberry stolon buds

BACKGROUND

Ramet propagation in strawberry (Fragaria × ananassa) is the most effective way in production. However, the lack of systematically phenotypic observations and high-throughput methods limits our ability to analyze the key factors regulating the heterogeneity in strawberry stolon buds.

RESULTS

From observation, we found that the axillary bud located in the first node quickly stepped into dormancy (DSB), after several bract and leaf buds were differentiated. The stolon apical meristem (SAM) degenerated as the new ramet leaf buds (RLB), and the new active axillary stolon buds (ASB) differentiated continually after the differentiation of the first leaf. Using the tandem mass tags (TMT) labeling method, a total of 7271 strawberry proteins were identified. Between ASB and DSB, the spliceosome DEPs, such as Ser/Arg-rich (SR) and heterogeneous nuclear ribonucleoprotein particle (hnRNP), showed the highest enrichment and high PPI connectivity. This indicated that the differences in DEPs (e.g., SF-3A and PK) at the transcriptional level may be causing the differences between the physiological statuses of ASB and DSB. As expected, the photosynthetic pre-form RLB mainly differentiated from ASB and DSB judging by the DEP enrichment of photosynthesis. However, there are still other specialized features of DEPs between RLB and DSB and between ASB and DSB. The DEPs relative to DNA duplication [e.g., minichromosome maintenance protein (MCM 2, 3, 4, 7)], provide a strong hint of functional gene duplication leading the bud heterogeneity between RLB and DSB. In addition, the top fold change DEP of LSH 10-like might be involved in the degeneration of SAM into RLBs, based on its significant function in modulating the plant shoot initiation. As for RLB/ASB, the phenylpropanoid biosynthesis pathway probably regulates the ramet axillary bud specialization, and further promotes the differentiation of xylem when ASB develops into a new stolon [e.g., cinnamyl alcohol dehydrogenase 1 (CAD1) and phenylalanine ammonia-lyase 1 (PAL1)].

CONCLUSIONS

By using phenotypic observation combined with proteomic networks with different types of strawberry stolon buds, the definite dormancy phase of DSB was identified, and the biological pathways and gene networks that might be responsible for heterogeneity among different stolon buds in strawberry were also revealed.

Plant Clonal Integration Mediates the Horizontal Redistribution of Soil Resources, Benefiting Neighboring Plants

Resources such as water taken up by plants can be released into soils through hydraulic redistribution and can also be translocated by clonal integration within a plant clonal network. We hypothesized that the resources from one (donor) microsite could be translocated within a clonal network, released into different (recipient) microsites and subsequently used by neighbor plants in the recipient microsite. To test these hypotheses, we conducted two experiments in which connected and disconnected ramet pairs of Potentilla anserina were grown under both homogeneous and heterogeneous water regimes, with seedlings of Artemisia ordosica as neighbors. The isotopes [(15)N] and deuterium were used to trace the translocation of nitrogen and water, respectively, within the clonal network. The water and nitrogen taken up by P. anserina ramets in the donor microsite were translocated into the connected ramets in the recipient microsites. Most notably, portions of the translocated water and nitrogen were released into the recipient microsite and were used by the neighboring A. ordosica, which increased growth of the neighboring A. ordosica significantly. Therefore, our hypotheses were supported, and plant clonal integration mediated the horizontal hydraulic redistribution of resources, thus benefiting neighboring plants. Such a plant clonal integration-mediated resource redistribution in horizontal space may have substantial effects on the interspecific relations and composition of the community and consequently on ecosystem processes.

Reverse engineering: a key component of systems biology to unravel global abiotic stress cross-talk

Understanding the global abiotic stress response is an important stepping stone for the development of universal stress tolerance in plants in the era of climate change. Although co-occurrence of several stress factors (abiotic and biotic) in nature is found to be frequent, current attempts are poor to understand the complex physiological processes impacting plant growth under combinatory factors. In this review article, we discuss the recent advances of reverse engineering approaches that led to seminal discoveries of key candidate regulatory genes involved in cross-talk of abiotic stress responses and summarized the available tools of reverse engineering and its relevant application. Among the universally induced regulators involved in various abiotic stress responses, we highlight the importance of (i) abscisic acid (ABA) and jasmonic acid (JA) hormonal cross-talks and (ii) the central role of WRKY transcription factors (TF), potentially mediating both abiotic and biotic stress responses. Such interactome networks help not only to derive hypotheses but also play a vital role in identifying key regulatory targets and interconnected hormonal responses. To explore the full potential of gene network inference in the area of abiotic stress tolerance, we need to validate hypotheses by implementing time-dependent gene expression data from genetically engineered plants with modulated expression of target genes. We further propose to combine information on gene-by-gene interactions with data from physical interaction platforms such as protein-protein or TF-gene networks.