Plums are rich in flavonoids, key contributors to fruit coloration and putative health benefits. We studied the impact of changes in ethylene and sugars in flavonoid metabolism-related pathways of the climacteric Santa Rosa and its non-climacteric mutant Sweet Miriam, throughout the postharvest period. Fruits were harvested at optimal maturity, subjected to ethylene treatments, and evaluated during storage. We examined transcript profiles of structural and regulatory genes of flavonoid-related pathways and their associated metabolites in skin and flesh, integrated with multivariate analyses of ethylene and sugar metabolism. Ethylene treatments were positively correlated with anthocyanin and negatively correlated with flavonol and flavan-3-ol metabolism. Sucrose and galactose were positively associated with anthocyanin concentration, while sorbitol, fructose, glucose and minor sugars were correlated with flavonol and flavan-3-ol metabolism. Our results support the notion that ethylene is playing key roles in shifting plum fruit flavonoid profiles, which are also associated with changes in fruit sugars.

The Arabidopsis vacuolar Na⁺/H⁺ transporters (NHXs) are important regulators of intracellular pH, Na⁺ and K⁺ homeostasis and necessary for normal plant growth, development, and stress acclimation. Arabidopsis contains four vacuolar NHX isoforms known as AtNHX1 to AtNHX4. The quadruple knockout nhx1nhx2nhx3nhx4, lacking any vacuolar NHX-type antiporter activity, displayed auxin-related phenotypes including loss of apical dominance, reduced root growth, impaired gravitropism and less sensitivity to exogenous IAA and NAA, but not to 2,4-D. In nhx1nhx2nhx3nhx4, the abundance of the auxin efflux carrier PIN2, but not PIN1, was drastically reduced at the plasma membrane and was concomitant with an increase in PIN2 labeled intracellular vesicles. Intracellular trafficking to the vacuole was also delayed in the mutant. Measurements of free IAA content and imaging of the auxin sensor DII-Venus, suggest that auxin accumulates in root tips of nhx1nhx2nhx3nhx4. Collectively, our results indicate that vacuolar NHX dependent cation/H⁺ antiport activity is needed for proper auxin homeostasis, likely by affecting intracellular trafficking and distribution of the PIN2 efflux carrier.

Improving biological nitrogen fixation (BNF) in cereal crops is a long-sought objective; however, no successful modification of cereal crops showing increased BNF has been reported. Here, we described a novel approach in which rice plants were modified to increase the production of compounds that stimulated biofilm formation in soil diazotrophic bacteria, promoted bacterial colonization of plant tissues and improved BNF with increased grain yield at limiting soil nitrogen contents. We first used a chemical screening to identify plant-produced compounds that induced biofilm formation in nitrogen-fixing bacteria and demonstrated that apigenin and other flavones induced BNF. We then used CRISPR-based gene editing targeting apigenin breakdown in rice, increasing plant apigenin contents and apigenin root exudation. When grown at limiting soil nitrogen conditions, modified rice plants displayed increased grain yield. Biofilm production also modified the root microbiome structure, favouring the enrichment of diazotrophic bacteria recruitment. Our results support the manipulation of the flavone biosynthetic pathway as a feasible strategy for the induction of biological nitrogen fixation in cereals and a reduction in the use of inorganic nitrogen fertilizers.

Receptor-like cytoplasmic kinases (RLCKs) are receptor kinases that lack extracellular ligand-binding domains and have emerged as a major class of signaling proteins that regulate plant cellular activities in response to biotic/abiotic stresses and endogenous extracellular signaling molecules. We have identified a rice RLCK (OsRLCK311) that was significantly higher in transgenic pSARK-IPT rice (Oryza sativa) that exhibited enhanced growth under saline conditions. Overexpression of OsRLCK311 full-length protein (RLCK311FL) and the C-terminus of OsRLCK311 (ΔN) in Arabidopsis confirmed its role in salinity tolerance, both in seedlings and mature plants. Protein interaction assays indicated that OsRLCK311 and ΔN interacted in-vivo with the plasma membrane AQP AtPIP2;1. The RLCK311-PIP2;1 binding led to alterations in the stomata response to ABA, which was characterized by more open stomata of transgenic plants. Moreover, OsRLCK311-ΔN effect in mediating enhanced plant growth under saline conditions was also observed in the perennial grass Brachypodium sylvaticum, confirming its role in both dicots and monocots species. Lastly, OsRLCK311 interacted with the rice OsPIP2;1. We suggest that the rice OsRLCK311 play a role in regulating the plant growth response under saline conditions via the regulation of the stomata response to stress. This role seems to be independent of the RLCK311 kinase activity, since the overexpression of the RLCK311 C-terminus (ΔN), which lacks the kinase full domain, has a similar phenotype to RLCK311FL.