Supplementation of Trichoderma improves the alteration of nutrient allocation and transporter genes expression in rice under nutrient deficiencies

Genome-wide identification of kiwifruit K+ channel Shaker family members and their response to low-K+ stress

BACKGROUND

'Hongyang' kiwifruit (Actinidia chinensis cv 'Hongyang') is a high-quality variety of A. chinensis with the advantages of high yield, early ripening, and high stress tolerance. Studies have confirmed that the Shaker K+ genes family is involved in plant uptake and distribution of potassium (K+).

RESULTS

Twenty-eight Shaker genes were identified and analyzed from the 'Hongyang' kiwifruit (A. chinensis cv 'Hongyang') genome. Subcellular localization results showed that more than one-third of the AcShaker genes were on the cell membrane. Phylogenetic analysis indicated that the AcShaker genes were divided into six subfamilies (I-VI). Conservative model, gene structure, and structural domain analyses showed that AcShaker genes of the same subfamily have similar sequence features and structure. The promoter cis-elements of the AcShaker genes were classified into hormone-associated cis-elements and environmentally stress-associated cis-elements. The results of chromosomal localization and duplicated gene analysis demonstrated that AcShaker genes were distributed on 18 chromosomes, and segmental duplication was the prime mode of gene duplication in the AcShaker family. GO enrichment analysis manifested that the ion-conducting pathway of the AcShaker family plays a crucial role in regulating plant growth and development and adversity stress. Compared with the transcriptome data of the control group, all AcShaker genes were expressed under low-K+stress, and the expression differences of three genes (AcShaker15, AcShaker17, and AcShaker22) were highly significant. The qRT-PCR results showed a high correlation with the transcriptome data, which indicated that these three differentially expressed genes could regulate low-K+ stress and reduce K+ damage in kiwifruit plants, thus improving the resistance to low-K+ stress. Comparison between the salt stress and control transcriptomic data revealed that the expression of AcShaker11 and AcShaker18 genes was significantly different and lower under salt stress, indicating that both genes could be involved in salt stress resistance in kiwifruit.

CONCLUSION

The results showed that 28 AcShaker genes were identified and all expressed under low K+ stress, among which AcShaker22 was differentially and significantly upregulated. The AcShaker22 gene can be used as a candidate gene to cultivate new varieties of kiwifruit resistant to low K+ and provide a reference for exploring more properties and functions of the AcShaker genes.

Molecular insights into the mutualism that induces iron deficiency tolerance in sorghum inoculated with Trichoderma harzianum

Iron (Fe) deficiency is a common mineral stress in plants, including sorghum. Although the soil fungus Trichoderma harzianum has been shown to mitigate Fe deficiency in some circumstances, neither the range nor mechanism(s) of this process are well understood. In this study, high pH-induced Fe deficiency in sorghum cultivated in pots with natural field soil exhibited a significant decrease in biomass, photosynthetic rate, transpiration rate, stomatal conductance, water use efficiency, and Fe-uptake in both the root and shoot. However, the establishment of T. harzianum colonization in roots of Fe-deprived sorghum showed significant improvements in morpho-physiological traits, Fe levels, and redox status. Molecular detection of the fungal ThAOX1 (L-aminoacid oxidase) gene showed the highest colonization of T. harzianum in the root tips of Fe-deficient sorghum, a location thus targeted for further analysis. Expression studies by RNA-seq and qPCR in sorghum root tips revealed a significant upregulation of several genes associated with Fe uptake (SbTOM2), auxin synthesis (SbSAURX15), nicotianamine synthase 3 (SbNAS3), and a phytosiderophore transporter (SbYS1). Also induced was the siderophore synthesis gene (ThSIT1) in T. harzianum, a result supported by biochemical evidence for elevated siderophore and IAA (indole acetic acid) levels in roots. Given the high affinity of fungal siderophore to chelate insoluble Fe3+ ions, it is likely that elevated siderophore released by T. harzianum led to Fe(III)-siderophore complexes in the rhizosphere that were then transported into roots by the induced SbYS1 (yellow-stripe 1) transporter. In addition, the observed induction of several plant peroxidase genes and ABA (abscisic acid) under Fe deficiency after inoculation with T. harzianum may have helped induce tolerance to Fe-deficiency-induced oxidative stress and adaptive responses. This is the first mechanistic explanation for T. harzianum's role in helping alleviate Fe deficiency in sorghum and suggests that biofertilizers using T. harzianum will improve Fe availability to crops in high pH environments.

Trichoderma asperellum boosts nitrogen accumulation and photosynthetic capacity of wolfberry (Lycium chinense) under saline soil stress

Trichoderma can promote plant growth under saline stress, but the mechanisms remain to be revealed. In this study, we investigate photosynthetic gas exchange, photosystem II (PSII) performance, nitrogen absorption and accumulation in a medicinal plant wolfberry (Lycium chinense) in saline soil supplemented with Trichoderma biofertilizer (TF). Larger nitrogen and biomass accumulation were found in plants supplemented with TF than with organic fertilizer (OF), suggesting that Trichoderma asperellum promoted plant growth and nitrogen accumulation under saline stress. T. asperellum strengthened root nitrogen (N) absorption according to greater increased root NH4+ and NO3- influxes under supplement with TF than OF, while nitrogen assimilative enzymes such as nitrate reductase, nitrite reductase and glutamine synthetase activities in roots and leaves were also stimulated. Thus, the elevated N accumulation derived from the induction of T. asperellum on nitrogen absorption and assimilation. Greater increased photosynthetic rate (Pn) and photosynthetic N-use efficiency under supplement with TF than OF illustrated that T. asperellum enhanced photosynthetic capacity and N utilization under saline stress. Although increased leaf stomatal conductance contributed to carbon (C) isotope fractionation under TF supplement, leaf 13C abundance was significantly increased by supplement with TF rather than OF, indicating that T. asperellum raised CO2 assimilation to a greater extent, reducing C isotope preference. Trichoderma asperellum optimized electron transport at PSII donor and acceptor sides under saline stress because of lower K and J steps in chlorophyll fluorescence transients under supplement with TF than OF. The amount of PSII active reaction centers was also increased by T. asperellum. Thus, PSII performance was upgraded, consistent with greater heightened delayed chlorophyll fluorescence transients and I1 peak under supplement with TF than OF. In summary, TF acted to increase N nutrient acquisition and photosynthetic C fixation resulting in enhanced wolfberry growth under saline soil stress.

A Salt-Tolerant Strain of Trichoderma longibrachiatum HL167 Is Effective in Alleviating Salt Stress, Promoting Plant Growth, and Managing Fusarium Wilt Disease in Cowpea

Salt stress is a constraint factor in agricultural production and restricts crops yield and quality. In this study, a salt-tolerant strain of Trichoderma longibrachiatum HL167 was obtained from 64 isolates showing significant salt tolerance and antagonistic activity to Fusarium oxysporum. T. longibrachiatum HL167 inhibited F. oxysporum at a rate of 68.08% in 200 mM NaCl, penetrated F. oxysporum under 200 mM NaCl, and eventually induced F. oxysporum hyphae breaking, according to electron microscope observations. In the pot experiment, pretreatment of cowpea seedlings with T. longibrachiatum HL167 reduced the accumulation level of ROS in tissues and the damage caused by salt stress. Furthermore, in the field experiment, it was discovered that treating cowpea with T. longibrachiatum HL167 before root inoculation with F. oxysporum can successfully prevent and control the development of cowpea Fusarium wilt, with the best control effect reaching 61.54%. Moreover, the application of HL 167 also improved the K+/Na+ ratio of cowpea, alleviated the ion toxicity of salt stress on cowpea, and HL167 was found to effectively colonize the cowpea roots. T. longibrachiatum HL167, which normally survives in saline–alkali environments and has the functions of disease prevention and plant growth promotion capabilities, has important research implications for improving the saline–alkali soil environment and for the sustainable development of green agriculture.

Biotic elicitor-induced changes in growth, antioxidative defense, and metabolites in an improved prickleless Solanum viarum

Solanum viarum serves as a raw material for the steroidal drug industry due to its alkaloid and glycoalkaloid content. Elicitation is well-known for measuring the increase in the yield of bioactive compounds in in vitro cultures. The current study was performed for the accumulation of metabolites viz. solasodine, solanidine, and α-solanine in S. viarum culture using microbial-based elicitors added in 1%, 3%, 5%, and 7% on 25^th and 35^th day of culture period and harvested on 45^th and 50^th days of culture cycle. The treatment of 3% Trichoderma reesei and Bacillus tequilensis culture filtrate (CF) significantly increased biomass, alkaloids/glycoalkaloid content, and yield in S. viarum. T. reesei was found to be the best treatment for enhanced growth (GI = 11.65) and glycoalkaloid yield (2.54 mg DW plant^-1) after the 50^th day of the culture cycle when added on the 25^th day. The abundance of gene transcripts involved in the biosynthesis of alkaloids/glycoalkaloids, revealed by quantitative real-time PCR expression analysis correlates with the accumulation of their respective metabolites in elicited plants. Biochemical analysis shows that elicited plants inhibited oxidative damage caused by reactive oxygen species by activating enzymes (superoxide dismutase and ascorbate peroxidase) as well as non-enzymatic antioxidant mechanisms (alkaloids, total phenols, total flavonoids, carotenoids, and proline). The findings of this study clearly demonstrate that the application of T. reesei and B. tequilensis CF at a specific dose and time significantly improve biomass as well as upregulates the metabolite biosynthetic pathway in an important medicinal plant- S. viarum. KEY POINTS: • Biotic elicitors stimulated the alkaloids/glycoalkaloid content in S. viarum plant cultures. • T. reesei was found to be most efficient for enhancing the growth and alkaloids content. • Elicited plants activate ROS based-defense mechanism to overcome oxidative damage.

Fungal Endophyte: An Interactive Endosymbiont With the Capability of Modulating Host Physiology in Myriad Ways

Endophytic fungi ubiquitously dwell inside the tissue-spaces of plants, mostly asymptomatically. They grow either intercellularly or intracellularly in a particular host plant to complete the whole or part of their life cycle. They have been found to be associated with almost all the plants occurring in a natural ecosystem. Due to their important role in the survival of plants (modulate photosynthesis, increase nutrient uptake, alleviate the effect of various stresses) they have been selected to co-evolve with their hosts through the course of evolution. Many years of intense research have discovered their tremendous roles in increasing the fitness of the plants in both normal and stressed conditions. There are numerous literature regarding the involvement of various endophytic fungi in enhancing plant growth, nutrient uptake, stress tolerance, etc. But, there are scant reports documenting the specific mechanisms employed by fungal endophytes to manipulate plant physiology and exert their effects. In this review, we aim to document the probable ways undertaken by endophytic fungi to alter different physiological parameters of their host plants. Our objective is to present an in-depth elucidation about the impact of fungal endophytes on plant physiology to make this evolutionarily conserved symbiotic interaction understandable from a broader perspective.