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Summary: Leucine‐rich repeat‐receptor‐like kinase (LRR‐RLK) is a large subfamily of plant RLKs; however, its role in cold tolerance is still unknown. A novel cold tolerance LRR‐RLK gene (MtCTLK1) in Medicago truncatula was identified using the transgenic lines overexpressing MtCTLK1 (MtCTLK1‐OE) and mtctlk1 lines with Tnt1 retrotransposon insertion. Compared with the wild‐type, MtCTLK1‐OE lines had increased cold tolerance and mtctlk1 showed decreased cold tolerance. The impaired cold tolerance in mtctlk1 could be complemented by the transgenic expression of MtCTLK1 or its homolog MfCTLK1 from Medicago falcata. Antioxidant enzyme activities and proline accumulation as well as transcript levels of the associated genes were increased in response to cold, with higher levels in MtCTLK1‐OE or lower levels in mtctlk1 lines as compared with wild type. C‐Repeat‐Binding Factors (CBFs) and CBF‐dependent cold‐responsive genes were also induced in response to cold, and higher transcript levels of CBFs and CBF‐dependent cold‐responsive genes were observed in MtCTLK1‐OE lines whereas lower levels in mtctlk1 mutants. The results validate the role of MtCTLK1 or MfCTLK1 in the regulation of cold tolerance through the CBF pathway, antioxidant defense system and proline accumulation. It also provides a valuable gene for the molecular breeding program to improve cold tolerance in crops. Significance Statement: A novel cold tolerance leucine‐rich repeat‐receptor‐like kinase was identified from Medicago truncatula. It confers cold tolerance through regulation on the C‐repeat‐binding factor cold response pathway, antioxidant defense, and proline accumulation. [ABSTRACT FROM AUTHOR]

Auxin induced in root culture (AIR12) is a single gene in Arabidopsis and codes for a mono‐heme cytochrome b, but it is unknown whether plant AIR12 is involved in abiotic stress responses. MfAIR12 was identified from Medicago falcata that is legume germplasm with great cold tolerance. Transcript levels of MfAIR12 and its homolog MtAIR12 from Medicago truncatula was induced under low temperature. Overexpression of MfAIR12 led to the accumulation of H2O2 in apoplast and enhanced cold tolerance, which was blocked by H2O2 scavengers, indicating that the increased cold tolerance was dependent upon the accumulated H2O2. In addition, declined cold tolerance was observed in Arabidopsis mutant air12, which could be restored by expressing MfAIR12. Compared to the wild type, higher levels of ascorbic acid and ascorbate redox state, as well as transcripts of the C repeat/dehydration responsive element‐binding factor (CBF) transcription factors and their downstream cold‐responsive genes, were observed in MfAIR12 transgenic lines, but lower levels of those in air12 mutant. It is suggested AIR12 confers cold tolerance as a result of the altered H2O2 in the apoplast that is signaling in the regulation of CBF cold response pathway and ascorbate homeostasis. AIR12 confers cold tolerance as a result of the altered H2O2 in apoplast that is signaling in the regulation of CBF pathway and its downstream cold‐responsive genes as well as ascorbic acid synthesis and redox state. [ABSTRACT FROM AUTHOR]

Summary: Alfalfa (Medicago sativa L.) is one of the most important forage crops throughout the world. Maximizing leaf retention during the haymaking process is critical for achieving superior hay quality and maintaining biomass yield. Leaf abscission process affects leaf retention. Previous studies have largely focused on the molecular mechanisms of floral organ, pedicel and seed abscission but scarcely touched on leaf and petiole abscission. This study focuses on leaf and petiole abscission in the model legume Medicago truncatula and its closely related commercial species alfalfa. By analysing the petiolule‐like pulvinus (plp) mutant in M. truncatula at phenotypic level (breakstrength and shaking assays), microscopic level (scanning electron microscopy and cross‐sectional analyses) and molecular level (expression level and expression pattern analyses), we discovered that the loss of function of PLP leads to an absence of abscission zone (AZ) formation and PLP plays an important role in leaflet and petiole AZ differentiation. Microarray analysis indicated that PLP affects abscission process through modulating genes involved in hormonal homeostasis, cell wall remodelling and degradation. Detailed analyses led us to propose a functional model of PLP in regulating leaflet and petiole abscission. Furthermore, we cloned the PLP gene (MsPLP) from alfalfa and produced RNAi transgenic alfalfa plants to down‐regulate the endogenous MsPLP. Down‐regulation of MsPLP results in altered pulvinus structure with increased leaflet breakstrength, thus offering a new approach to decrease leaf loss during alfalfa haymaking process. [ABSTRACT FROM AUTHOR]

Abstract: Ethylene responsive factor (ERF) subfamily transcription factors play an important role in plant abiotic and biotic stress tolerance. A cold responsive ERF, MfERF1, was isolated from Medicago falcata, an important forage legume that has great cold tolerance. Overexpression of MfERF1 resulted in an increased tolerance to freezing and chilling in transgenic tobacco plants, whereas down‐regulation of the ortholog of MfERF1 in Medicago truncatula resulted in reduced freezing tolerance in RNAi plants. Higher transcript levels of some stress responsive genes (CHN50, OSM, ERD10C, and SAMS) and those involved in spermidine (Spd) and spermine (Spm) synthesis (SAMDC1, SAMDC2, SPDS1, SPDS2, and SPMS) and catabolism (PAO) were observed in transgenic plants than in wild type. However, neither Spd nor Spm level was accumulated in transgenic plants as a result of promoted polyamine oxidase activity. Transgenic plants had higher activities of antioxidants associated with the induced encoding genes including Cu, Zn‐SOD, CAT1, CAT2, CAT3, and cpAPX and accumulated more proline associated with induced P5CS and reduced PROX2 transcription as compared with wild type. The results suggest that MfERF1 confers cold tolerance through promoted polyamine turnover, antioxidant protection, and proline accumulation. [ABSTRACT FROM AUTHOR]

Dwarfism and drought tolerance are 2 valuable traits in breeding of many crops. In this study, we report the novel physiological roles of cholesterol in regulation of plant growth and drought tolerance. Compared with the wild type, sterol-C24-methyltransferase 1 (SMT1) gene transcript was greatly reduced in a bermudagrass mutant with dwarfism and enhanced drought tolerance, accompanied with cholesterol accumulation, elevated transcript levels of a small group of genes including SAMDC, and increased concentrations of putrescine (Put), spermidine (Spd), and spermine (Spm). Knock-down of OsSMT1 expression by RNA interference resulted in similar phenotypic changes in transgenic rice. Moreover, exogenously applied cholesterol also led to elevated transcripts of a similar set of genes, higher levels of Put, Spd, and Spm, improved drought tolerance, and reduced plant height in both bermudagrass and rice. We revealed that it is Spm, but not Spd, that is responsible for the height reduction in bermudagrass and rice. In conclusion, we suggest that cholesterol induces expression of SAMDC and leads to dwarfism and elevated drought tolerance in plants as a result of the promoted Spd and Spm synthesis. [ABSTRACT FROM AUTHOR]

Abscisic acid (ABA) regulates plant adaptive responses to various environmental stresses, while Lascorbic acid (AsA) that is also named vitamin C is an important antioxidant and involves in plant stress tolerance and the immune system in domestic animals. Transgenic tobacco (Nicotiana tabacum L.) and stylo [Stylosanthes guianensis (Aublet) Swartz], a forage legume, plants coexpressing stylo 9-cis-epoxycarotenoid dioxygenase (SgNCED1) and yeast D-arabinono-1,4- lactone oxidase (ALO) genes were generated in this study, and tolerance to drought and chilling was analysed in comparison with transgenic tobacco overexpressing SgNCED1 or ALO and the wild-type plants. Compared to the SgNCED1 or ALO transgenic plants, in which only ABA or AsA levels were increased, both ABA and AsA levels were increased in transgenic tobacco and stylo plants co-expressing SgNCED1 and ALO genes. Compared to the wild type, an enhanced drought tolerance was observed in SgNCED1 transgenic tobacco plants with induced expression of drought-responsive genes, but not in ALO plants, while an enhanced chilling tolerance was observed in ALO transgenic tobaccos with induced expression of cold-responsive genes, but not in SgNCED1 plants. Co-expression of SgNCED1 and ALO genes resulted in elevated tolerance to both drought and chilling in transgenic tobacco and stylo plants with induced expression of both drought and cold-responsive genes. Our result suggests that co-expression of SgNCED1 and ALO genes is an effective way for use in forage plant improvement for increased tolerance to drought and chilling and nutrition quality. [ABSTRACT FROM AUTHOR]

Nuclear factor Y (NF-Y) is a ubiquitous transcription factor formed by three distinct subunits, namely NF-YA, NF-YB and NF-YC. A stress-responsive cDNA of NF-YC ( Cdt-NF-YC1) was isolated from triploid bermudagrass ( Cynodon dactylon × Cynodon transvaalensis), and its role in abiotic stress tolerance was investigated in this study. Cdt-NF-YC1 transcript was detected in all vegetative tissues with higher levels being observed in roots. Transcription of Cdt-NF-YC1 in leaves was induced by dehydration, salinity, and treatments with abscisic acid (ABA), hydrogen peroxide (H2O2) or nitric oxide (NO), but not altered by cold. The dehydration- or salt-induced transcription of Cdt-NF-YC1 was blocked by inhibitor of ABA synthesis and scavenger of H2O2 or NO, indicating that ABA, H2O2 and NO were involved in the dehydration- and salt-induced transcription of Cdt-NF-YC1. Overexpression of Cdt-NF-YC1 resulted in elevated tolerance to drought and salt stress and increased sensitivity to ABA in transgenic rice. Transcript levels of stress/ABA responsive genes ( OsLEA3, OsRAB16A, OsLIP9 and OsP5CS1), ABA synthesis and signalling genes ( OsNCED3 and OsABI2), and ABA-independent genes ( OsDREB1A, OsDREB1B and OsDREB2A) were substantially higher in transgenic rice than in wild-type plants. The results suggested that that Cdt-NF-YC1 is a good candidate gene to increase drought and salinity tolerance in transgenic rice through modulating gene regulation in both ABA-dependent and ABA-independent pathways. [ABSTRACT FROM AUTHOR]