ABSCISIC ACID-INSENSITIVE 5-KIP-RELATED PROTEIN 1-SHOOT MERISTEMLESS modulates reproductive development of Arabidopsis.

Soil (or plant) water deficit accelerates plant reproduction. However, the underpinning molecular mechanisms remain unknown. By modulating cell division/number, ABSCISIC ACID-INSENSITIVE 5 (ABI5), a key bZIP (basic (region) leucine zippers) transcription factor, regulates both seed development and abiotic stress responses. The KRP (KIP-RELATED PROTEIN) cyclin-dependent kinases (CDKs) play an essential role in controlling cell division, and SHOOT MERISTEMLESS (STM) plays a key role in the specification of flower meristem identity. Here, our findings show that abscisic acid (ABA) signaling and/or metabolism in adjust reproductive outputs (such as rosette leaf number and open flower number) under water-deficient conditions in Arabidopsis (Arabidopsis thaliana) plants. Reproductive outputs increased under water-sufficient conditions but decreased under water-deficient conditions in the ABA signaling/metabolism mutants abscisic acid2-1 (aba2-1), aba2-11, abscisic acid insensitive3-1 (abi3-1), abi4-1, abi5-7, and abi5-8. Further, under water-deficient conditions, ABA induced-ABI5 directly bound to the promoter of KRP1, which encodes a CDK that plays an essential role in controlling cell division, and this binding subsequently activated KRP1 expression. In turn, KRP1 physically interacted with SHOOT MERISTEMLESS (STM), which functions in the specification of flower meristem identity, promoting STM degradation. We further demonstrate that reproductive outputs are adjusted by the ABI5-KRP1-STM molecular module under water-deficient conditions. Together, our findings reveal the molecular mechanism by which ABA signaling and/or metabolism regulate reproductive development under water-deficient conditions. These findings provide insights that may help guide crop yield improvement under water deficiency.

Glucose status within dark-grown etiolated cotyledons determines seedling de-etiolation upon light irradiation.

Exposure of dark-grown etiolated seedlings to light triggers the transition from skotomorphogenesis/etiolation to photomorphogenesis/de-etiolation. In the life cycle of plants, de-etiolation is essential for seedling development and plant survival. The mobilization of soluble sugars (glucose [Glc], sucrose, and fructose) derived from stored carbohydrates and lipids to target organs, including cotyledons, hypocotyls, and radicles, underpins de-etiolation. Therefore, dynamic carbohydrate biochemistry is a key feature of this phase transition. However, the molecular mechanisms coordinating carbohydrate status with the cellular machinery orchestrating de-etiolation remain largely opaque. Here, we show that the Glc sensor HEXOKINASE 1 (HXK1) interacts with GROWTH REGULATOR FACTOR5 (GRF5), a transcriptional activator and key plant growth regulator, in Arabidopsis (Arabidopsis thaliana). Subsequently, GRF5 directly binds to the promoter of phytochrome A (phyA), encoding a far-red light (FR) sensor/cotyledon greening inhibitor. We demonstrate that the status of Glc within dark-grown etiolated cotyledons determines the de-etiolation of seedlings when exposed to light irradiation by the HXK1-GRF5-phyA molecular module. Thus, following seed germination, accumulating Glc within dark-grown etiolated cotyledons stimulates a HXK1-dependent increase of GRF5 and an associated decrease of phyA, triggering the perception, amplification, and relay of HXK1-dependent Glc signaling, thereby facilitating the de-etiolation of seedlings following light irradiation. Our findings, therefore, establish how cotyledon carbohydrate signaling under subterranean darkness is sensed, amplified, and relayed, determining the phase transition from skotomorphogenesis to photomorphogenesis on exposure to light irradiation.

Salinicola tamaricis sp. nov., a heavy-metal-tolerant, endophytic bacterium isolated from the halophyte Tamarix chinensis Lour.

A Gram-stain-negative, rod-shaped bacterium, strain F01T, was isolated from leaves of Tamarix chinensis Lour. The isolate grew optimally at 30 °C, at pH 7.0 and with 5.0 % (w/v) NaCl, and showed a high tolerance to manganese, lead, nickel, ferrous ions and copper ions. The major fatty acids were C18 : 1ω7c and C16 : 0, and the predominant respiratory quinone was Q-9. Polar lipids were dominated by diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, unidentified aminoglycolipids and phospholipids. The DNA G+C content was 65.8 %. Based on multilocus phylogenetic analysis, strain F01T belonged to the genus Salinicola, with highest 16S rRNA gene sequence similarity to Salinicola peritrichatus CGMCC 1.12381T (97.7 %). The level of DNA-DNA hybridization between strain F01T and closely related Salinicola strains was well below 70 %. According to the phenotypic, genetic and chemotaxonomic data, strain F01T is considered to represent a novel species in the genus Salinicola, for which the name Salinicola tamaricis sp. nov. is proposed. The type strain is F01T (=CCTCC AB 2015304T=KCTC 42855T).