Understanding the regulation of cereal grain filling: The way forward.

During grain filling, starch and other nutrients accumulate in the endosperm; this directly determines grain yield and grain quality in crops such as rice (Oryza sativa), maize (Zea mays), and wheat (Triticum aestivum). Grain filling is a complex trait affected by both intrinsic and environmental factors, making it difficult to explore the underlying genetics, molecular regulation, and the application of these genes for breeding. With the development of powerful genetic and molecular techniques, much has been learned about the genes and molecular networks related to grain filling over the past decades. In this review, we highlight the key factors affecting grain filling, including both biological and abiotic factors. We then summarize the key genes controlling grain filling and their roles in this event, including regulators of sugar translocation and starch biosynthesis, phytohormone-related regulators, and other factors. Finally, we discuss how the current knowledge of valuable grain filling genes could be integrated with strategies for breeding cereal varieties with improved grain yield and quality.

Plant volatiles guide the new pest Dichelops furcatus to feed on corn seedlings.

BACKGROUND: Recently, in temperate and neotropical regions of South America the generalist stink bug Dichelops furcatus (Hemiptera: Pentatomidae) became a new pest of corn (Zea mays) seedlings. Implementation of no-tillage cultivation system left organic matter covering the soil, which shelters adults of stink bugs during winter. In spring, corn is sowed under soybean stubble and D. furcatus adults start to feed on seedlings. To determine corn-derived volatile organic compounds (VOCs) that attract this stink bug species, we evaluated stink bug preferences from two corn hybrids with contrast germplasm backgrounds, a temperate and a tropical hybrid. RESULTS: Stink bugs preferred to feed on temperate seedlings rather than on the tropical ones. GC-MS and PCA analysis of VOCs suggested that hybrids emitted contrasting blends. Linalool represented 68% of total VOCs emitted from temperate corn, while in the tropical hybrid this compound represented 48%. Olfactometer experiments demonstrated that linalool was attractive to stink bugs. However, 2 h of D. furcatus attack induced emission of 14 additional VOCs in temperate seedlings, and olfactometer bioassay and blend of VOCs emission suggested that perceived volatiles by stink bugs induced feeding avoidance. The increment of VOCs emission was associated with the induction of JA, JA-Ile, ABA, and IAA, and decreasing of SA concentrations. CONCLUSION: This is the first time showing a complete profile of defensive phytohormones induced by stink bugs feeding on corn, and further demonstrating that a blend of corn seedling-associated VOCs, mainly composed by linalool, modulates D. furcatus adults' behavior and feeding preferences. © 2021 Society of Chemical Industry.

Rhizobacteria AK1 remediates the toxic effects of salinity stress via regulation of endogenous phytohormones and gene expression in soybean.

Salinity stress adversely affects the growth and productivity of different crops. In the present study, we isolated the rhizospheric bacteria Arthrobacter woluwensis AK1 from Pohang beach, South Korea and determined its plant growth-promoting potential under NaCl salt stress (0, 100, and 200 mM). AK1 has phosphate-solubilizing activity and produce siderophores, organic acids, and phytohormones such as gibberellic acid (GA) and indole-3-acetic acid (IAA) that significantly alleviate sodium chloride (NaCl) stress and increase all plant growth attributes. Furthermore, inoculation of AK1 significantly decreased endogenous abscisic acid (ABA) content, extensively regulated the antioxidant activities and mitigated NaCl stress. Similarly, inductively coupled plasma mass spectrometry results showed that soybean plants inoculated with AK1 significantly decreased the amount of sodium (Na+) uptake during NaCl stress after 6 and 12 days. Four genes, auxin resistant 1 (GmLAX1), potassium channel AKT2 (GmAKT2), soybean salt tolerance 1 (GmST1), and salt tolerance-associated gene on chromosome 3 (GmSALT3) were up-regulated, while two genes chloride channel gene (GmNHX1) and Na+/H+ antiporter (GmCLC1) were down-regulated in soybean AK1treated plants. In conclusion, AK1 can mitigate salinity stress, increase plant growth and could be utilized as an eco-friendly bio-fertilizer under salinity stress.

Corrigendum: Phytohormone and Putative Defense Gene Expression Differentiates the Response of 'Hayward' Kiwifruit to Psa and Pfm Infections.

[This corrects the article on p. 1366 in vol. 8, PMID: 28824694.].

Phytohormone and Putative Defense Gene Expression Differentiates the Response of 'Hayward' Kiwifruit to Psa and Pfm Infections.

Pseudomonas syringae pv. actinidiae (Psa) and Pseudomonas syringae pv. actinidifoliorum (Pfm) are closely related pathovars infecting kiwifruit, but Psa is considered one of the most important global pathogens, whereas Pfm is not. In this study of Actinidia deliciosa 'Hayward' responses to the two pathovars, the objective was to test whether differences in plant defense responses mounted against the two pathovars correlated with the contrasting severity of the symptoms caused by them. Results showed that Psa infections were always more severe than Pfm infections, and were associated with highly localized, differential expression of phytohormones and putative defense gene transcripts in stem tissue closest to the inoculation site. Phytohormone concentrations of jasmonic acid (JA), jasmonate isoleucine (JA-Ile), salicylic acid (SA) and abscisic acid were always greater in stem tissue than in leaves, and leaf phytohormones were not affected by pathogen inoculation. Pfm inoculation induced a threefold increase in SA in stems relative to Psa inoculation, and a smaller 1.6-fold induction of JA. Transcript expression showed no effect of inoculation in leaves, but Pfm inoculation resulted in the greatest elevation of the SA marker genes, PR1 and glucan endo-1,3-beta-glucosidase (ß-1,3-glucosidase) (32- and 25-fold increases, respectively) in stem tissue surrounding the inoculation site. Pfm inoculation also produced a stronger response than Psa inoculation in localized stem tissue for the SA marker gene PR6, jasmonoyl-isoleucine-12-hydrolase (JIH1), which acts as a negative marker of the JA pathway, and APETALA2/Ethylene response factor 2 transcription factor (AP2 ERF2), which is involved in JA/SA crosstalk. WRKY40 transcription factor (a SA marker) was induced equally in stems by wounding (mock inoculation) and pathovar inoculation. Taken together, these results suggest that the host appears to mount a stronger, localized, SA-based defense response to Pfm than Psa.

The Combination of Trichoderma harzianum and Chemical Fertilization Leads to the Deregulation of Phytohormone Networking, Preventing the Adaptive Responses of Tomato Plants to Salt Stress.

Plants have evolved effective mechanisms to avoid or reduce the potential damage caused by abiotic stresses. In addition to biocontrol abilities, Trichoderma genus fungi promote growth and alleviate the adverse effects caused by saline stress in plants. Morphological, physiological, and molecular changes were analyzed in salt-stressed tomato plants grown under greenhouse conditions in order to investigate the effects of chemical and biological fertilizations. The application of Trichoderma harzianum T34 to tomato seeds had very positive effects on plant growth, independently of chemical fertilization. The application of salt stress significantly changed the parameters related to growth and gas-exchange rates in tomato plants subject to chemical fertilization. However, the gas-exchange parameters were not affected in unfertilized plants under the same moderate saline stress. The combined application of T34 and salt significantly reduced the fresh and dry weights of NPK-fertilized plants, while the opposite effects were detected when no chemical fertilization was applied. Decaying symptoms were observed in salt-stressed and chemically fertilized plants previously treated with T34. This damaged phenotype was linked to significantly higher intercellular CO2 and slight increases in stomatal conductance and transpiration, and to the deregulation of phytohormone networking in terms of significantly lower expression levels of the salt overlay sensitivity 1 (SOS1) gene, and the genes involved in signaling abscisic acid-, ethylene-, and salicylic acid-dependent pathways and ROS production, in comparison with those observed in salt-challenged NPK-fertilized plants.