Glomus mosseae and Pseudomonas fluorescens Application Sustains Yield and Promote Tolerance to Water Stress in Helianthus annuus L

The inoculation of sunflower (Helianthus annuus L.) plants with arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) can significantly enhance its growth and yield in a sustainable manner. Drought tolerance is mediated by a combination of direct AMF and PGPR benefits that boost the plant’s natural ability to cope with stress, whereas drought mitigation is mediated by indirect AMF and PGPR benefits and increased water uptake. An experiment was carried out to demonstrate the interactive effects of AMF (Glomus mosseae) alone or in association with PGPR (Pseudomonas fluorescens) under water-stressed conditions in order to assess their biofertilizer efficiency. Accordingly, various morphological and biochemical parameters were studied, and the results suggested that all the co-inoculation treatments displayed beneficial effects. Still, the combination of G. mosseae + P. fluorescens showed the maximum increment in all the parameters considered, i.e., plant height and weight, leaves length and width, number of leaves per plant, specific leaf weight, relative leaf water content (RLWC), photosynthetic efficiency, seed length, width, and area, seed yield per plant, number of seeds per flower, days to 50% flowering, days to maturity, flower and head diameter, harvest index, oil content, fatty acid composition (palmitic acid, oleic acid, stearic acid, and linoleic acid), and total yield. The improvement in different parameters may be attributed to the increased availability of nutrients due to the symbiotic association of AMF and PGPR with plant roots along with enhanced root structures for more water absorption under stressed conditions. Therefore, the results suggested that they offer a promising bio-control strategy for crop protection as biofertilizers combined in one formulation.

Phytohormones Producing Acinetobacter bouvetii P1 Mitigates Chromate Stress in Sunflower by Provoking Host Antioxidant Response

Different physical and chemical techniques are used for the decontamination of Cr+6 contaminated sites. The techniques are expensive, laborious, and time-consuming. However, remediation of Cr+6 by microbes is viable, efficient, and cost-effective. In this context, plant growth-promoting rhizobacteria Acinetobacter bouvetii P1 isolated from the industrial zone was tested for its role in relieving Cr+6 induced oxidative stress in sunflower. At the elevated Cr+6 levels and in the absence of P1, the growth of the sunflower plants was inhibited. In contrast, the selected strain P1 restored the sunflower growth under Cr+6 through plant growth-promoting interactions. Specifically, P1 biotransformed the Cr+6 into a stable and less toxic Cr+3 form, thus avoiding the possibility of phytotoxicity. On the one hand, the P1 strengthened the host antioxidant system by triggering higher production of enzymatic antioxidants, including catalases, ascorbate peroxidase, superoxide dismutase, and peroxidase. Similarly, P1 also promoted higher production of nonenzymatic antioxidants, such as flavonoids, phenolics, proline, and glutathione. Apart from the bioremediation, P1 solubilized phosphate and produced indole acetic acid, gibberellic acid, and salicylic acid. The production of phytohormones not only helped the host plant growth but also mitigated the harsh condition posed by the elevated levels of Cr+6. The findings mentioned above suggest that P1 may serve as an excellent phyto-stimulant and bio-remediator in a heavy metal-contaminated environment.

Comparative genomic analysis of MYB transcription factors for cuticular wax biosynthesis and drought stress tolerance in Helianthus annuus L

Sunflower is an important oil-seed crop in Pakistan, it is mainly cultivated in the spring season. It is severely affected by drought stress resulting in lower yield. Cuticular wax acts as the first defense line to protect plants from drought stress condition. It seals the aerial parts of plants and reduce the water loss from leaf surfaces. Various myeloblastosis (MYB) transcription factors (TFs) are involved in biosynthesis of epicuticular waxes under drought-stress. However, less information is available for MYB, TFs in drought stress and wax biosynthesis in sunflower. We used different computational tools to compare the Arabidopsis MYB, TFs involved in cuticular wax biosynthesis and drought stress tolerance with sunflower genome. We identified three putative MYB genes (MYB16, MYB94 and MYB96) in sunflower along with their seven homologs in Arabidopsis. Phylogenetic association of MYB TFs in Arabidopsis and sunflower indicated strong conservation of TFs in plant species. From gene structure analysis, it was observed that intron and exon organization was family-specific. MYB TFs were unevenly distributed on sunflower chromosomes. Evolutionary analysis indicated the segmental duplication of the MYB gene family in sunflower. Quantitative Real-Time PCR revealed the up-regulation of three MYB genes under drought stress. The gene expression of MYB16, MYB94 and MYB96 were found many folds higher in experimental plants than control. The present study provided the first insight into MYB TFs family's characterization in sunflower under drought stress conditions and wax biosynthesis TFs.

Phytohormones producing rhizobacterium alleviates chromium toxicity in Helianthus annuus L. by reducing chromate uptake and strengthening antioxidant system

Contamination of agricultural land with heavy metal is a serious biological and environmental issue. Such threat can be challenged by exploring the plant symbiotic microbes that can improve plant growth through phyto-hormones secretion and chromate chelation. In the current study, chromate resistant rhizospheric Staphylococcus arlettae strain MT4 was isolated from the rhizosphere of Malvestrum tricuspadatum L. The strain showed potential to secrete phytohormones and plant growth promoting secondary metabolites under induced chromate stress, making it a best suitable candidate in chromate stress alleviation. Moreover, the rhizobacterium MT4 significantly promoted the net assimilation and relative growth rate of sunflower grown in the presence of chromate (100 ppm). Chromate stress alleviation strategy of MT4 strain was three-fold. MT4 alleviated chromate stress and promoted the sunflower growth by suppressing the chromate intake by the host, modulating phytohormones and strengthening of the host's antioxidant system. The improved antioxidant system was confirmed by noticing lower ROS accumulation and improved ROS scavenging, lower peroxidase activity and higher accumulation of phenols and flavonoids.