Physiological traits determining high adaptation potential of sweet briar (Rosa rubiginosa L.) at early stage of growth to dry lands

The role of invasive plant species in drought resilience in agriculture: the case of sweet briar (Rosa rubiginosa L.)

Sweet briar (Rosa rubiginosa) belongs to the group of wild roses. Under natural conditions it grows throughout Europe, and was introduced also into the southern hemisphere, where it has efficiently adapted to dry lands. This review focuses on the high adaptation potential of sweet briar to soil drought in the context of global climatic changes, especially considering steppe formation and desertification of agricultural, orchard, and horticultural areas. We provide a comprehensive overview of current knowledge on sweet briar traits associated with drought tolerance and particularly water use efficiency, sugar accumulation, accumulation of CO2 in intercellular spaces, stomatal conductance, gibberellin level, effective electron transport between photosystem II and photosystem I, and protein content. We discuss the genetics and potential applications in plant breeding and suggest future directions of study concerning invasive populations of R. rubiginosa. Finally, we point out that sweet briar can provide new genes for breeding in the context of depleting gene pools of the crop plants.

Non-rolling flag leaves use an effective mechanism to reduce water loss and light-induced damage under drought stress

BACKGROUND AND AIMS

The study reports on four different types of flag leaf rolling under soil drought in relation to the level of cell wall-bound phenolics. The flag leaf colonization by aphids, as a possible bioindicator of the accumulation of cell wall-bound phenolics, was also estimated.

METHODS

The proteins of the photosynthetic apparatus that form its core and are crucial for maintaining its stability (D1/PsbA protein), limit destructive effects of light (PsbS, a protein binding carotenoids in the antennas) and participate in efficient electron transport between photosystems II (PSII) and PSI (Rieske iron-sulfur protein of the cytochrome b6f complex) were evaluated in two types of flag leaf rolling. Additionally, biochemical and physiological reactions to drought stress in rolling and non-rolling flag leaves were compared.

KEY RESULTS

The study identified four types of genome-related types of flag leaf rolling. The biochemical basis for these differences was a different number of phenolic molecules incorporated into polycarbohydrate structures of the cell wall. In an extreme case of non-rolling dehydrated flag leaves, they were found to accumulate high amounts of cell wall-bound phenolics that limited cell water loss and protected the photosynthetic apparatus against excessive light. PSII was also additionally protected against excess light by the accumulation of photosynthetic apparatus proteins that ensured stable and efficient transport of excitation energy beyond PSII and its dissipation as far-red fluorescence and heat. Our analysis revealed a new type of flag leaf rolling brought about by an interaction between wheat and rye genomes, and resulting in biochemical specialization of flexible, rolling and rigid, non-rolling parts of the flag leaf. The study confirmed limited aphid colonization of the flag leaves with enhanced content of cell wall-bound phenolics.

CONCLUSIONS

Non-rolling leaves developed effective adaptation mechanisms to reduce both water loss and photoinhibitory damage to the photosynthetic apparatus under drought stress.

Physiological Comparison of Wheat and Maize Seedlings Responses to Water Stresses

The aim of the study was to investigate specific responses of spring wheat (C3 photosynthesis) and maize (C4 photosynthesis) to drought and flooding stress. Analyses of water content, gas exchange intensity, photosynthetic apparatus activity, chlorophyll content, plant height and biological membrane integrity were performed on the 10th day of drought and flooding in both species at the third leaf stage. A specific response of wheat under both drought and flooding conditions involved an increase in ETo/RC ratio, describing electron transport flux converted into a single reaction center in PSII. Correlations between electrolyte leakage and the probability of electron transport beyond the plastoquinone QA, and the amount of energy used for the electron transport were also found. A specific response of maize during flooding was the increase of stomatal conductance. Additionally, a significant correlation between PN/Ci and relative water content was exhibited. Furthermore, the parameters differentiating the studied species only under stressful conditions were rendered. The application of such parameters can be widely used, e.g., for studying the reaction of a potential cultivars to drought and flooding. Providing such information to potential farmers can help better select cultivars for their environmental conditions.

Comparative Transcriptome and Weighted Gene Co-expression Network Analysis Identify Key Transcription Factors of Rosa chinensis 'Old Blush' After Exposure to a Gradual Drought Stress Followed by Recovery

Rose is one of the most fundamental ornamental crops, but its yield and quality are highly limited by drought. The key transcription factors (TFs) and co-expression networks during rose’s response to drought stress and recovery after drought stress are still limited. In this study, the transcriptomes of leaves of 2-year-old cutting seedlings of Rosa chinensis ‘Old Blush’ from three continuous droughted stages (30, 60, 90 days after full watering) and rewatering were analyzed using RNA sequencing. Weighted gene co-expression network analysis (WGCNA) was used to construct a co-expression network, which was associated with the physiological traits of drought response to discovering the hub TFs involved in drought response. More than 45 million high-quality clean reads were generated from the sample and used for comparison with the rose reference genome. A total of 46433 differentially expressed genes (DEGs) were identified. Gene Ontology (GO) term enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that drought stress caused significant changes in signal transduction, plant hormones including ABA, auxin, brassinosteroid (BR), cytokinin, ethylene (ET), jasmonic acid (JA) and salicylic acid (SA), primary and secondary metabolism, and a certain degree of recovery after rewatering. Gene co-expression analysis identified 18 modules, in which four modules showed a high degree of correlation with physiological traits. In addition, 42 TFs including members of NACs, WRKYs, MYBs, AP2/ERFs, ARFs, and bHLHs with high connectivity in navajowhite1 and blue modules were screened. This study provides the transcriptome sequencing report of R. chinensis ‘Old Blush’ during drought stress and rewatering process. The study also identifies the response of candidate TFs to drought stress, providing guidelines for improving the drought tolerance of the rose through molecular breeding in the future.

Phytohormone synthesis pathways in sweet briar rose (Rosa rubiginosa L.) seedlings with high adaptation potential to soil drought

The study aimed to determine the phytohormone profile of sweet briar rose (Rosa rubiginosa L.) seedlings and privileged synthesis pathways of individual hormones including gibberellins, cytokinins and auxins in response to long-term soil drought. We detected eight gibberellins, nine auxins and fifteen cytokinins. Abscisic acid (ABA) was also detected as a sensitive indicator of water stress. Thirty days of soil drought induced significant increase of ABA content and species-specific quantitative changes of other phytohormones. We established preferred synthesis pathways for three gibberellins, six auxins and eight cytokinins. Both an increase and decrease in gibberellin and cytokinin levels may modulate sweet briar's response to soil water shortage. In the case of auxins, induction of effective adaptation mechanisms to extremely dry environments is mostly triggered by their rising levels. Under drought stress, sweet briar seedlings increased their gibberellin pool at the expense of reducing the pool of cytokinins and auxins. This may indicate a specific role of gibberellins in adaptation mechanisms to long-term soil water deficit developed by sweet briar.