A L-type lectin gene is involved in the response to hormonal treatment and water deficit in Volkamer lemon

Aluminium stress tolerance by Citrus plants: a consolidated review

Aluminium, a metallic element abundant in soils as aluminosilicates minerals, poses a toxic threat to plants, particularly in acidic soil conditions, thereby affecting their growth and development. Given their adaptability to diverse soil and climate conditions, Citrus plants have gained significant attention regarding their tolerance to Aluminium toxicity. In the North-eastern region of India, where soils are often slightly acidic with elevated aluminium levels, Citrus species are predominantly found. Understanding the tolerance mechanisms of these Citrus fruits and screening wild Citrus species for their adaptability to abiotic stresses is crucial for enhancing fruit production. Numerous investigations have demonstrated that Citrus species exhibit remarkable tolerance to aluminium contamination, surpassing the typical threshold of 30% incidence. When cultivated in acidic soils, Citrus plants encounter restricted root growth and reduced nutrient and moisture uptake, leading to various nutrient deficiency symptoms. However, promisingly, certain Citrus species such as Citrus jambhiri (Rough lemon), Poncirus trifoliata, Citrus sinensis, and Citrus grandis have shown considerable aluminium tolerance. This comprehensive review delves into the subject of aluminium toxicity and its implications, while also shedding light on the mechanisms through which Citrus plants develop tolerance to this element.

Identification of the Virulence Factors of Candidatus Liberibacter asiaticus via Heterologous Expression in Nicotiana benthamiana using Tobacco Mosaic Virus

Huanglongbing (HLB), also known as citrus greening, is the most destructive disease of citrus worldwide. HLB is associated with the non-culturable bacterium, Candidatus Liberibacter asiaticus (CaLas) in the United States. The virulence mechanism of CaLas is largely unknown, partly because of the lack of a mutant library. In this study, Tobacco mosaic virus (TMV) and Nicotiana benthamiana (N. benthamiana) were used for large-scale screening of the virulence factors of CaLas. Agroinfiltration of 60 putative virulence factors in N. benthamiana led to the identification of four candidates that caused severe symptoms in N. benthamiana, such as growth inhibition and cell death. CLIBASIA_05150 and CLIBASIA_04065C (C-terminal of CLIBASIA_04065) could cause cell death in the infiltrated leaves at five days post infiltration. Two low-molecular-weight candidates, CLIBASIA_00470 and CLIBASIA_04025, could inhibit plant growth. By converting start codon to stop codon or frameshifting, the four genes lost their harmful effects to N. benthamiana. It indicated that the four virulence factors functioned at the protein level rather than at the RNA level. The subcellular localization of the four candidates was determined by confocal laser scanning microscope. CLIBASIA_05150 located in the Golgi apparatus; CLIBASIA_04065 located in the mitochondrion; CLIBASIA_00470 and CLIBASIA_04025 distributed in cells as free GFP. The host proteins interacting with the four virulence factors were identified by yeast two-hybrid. The host proteins interacting with CLIBASIA_00470 and CLIBASIA_04025 were overlapping. Based on the phenotypes, the subcellular localization and the host proteins identified by yeast two-hybrid, CLIBASIA_00470 and CLIBASIA_04025, functioned redundantly. The hypothesis of CaLas virulence was proposed. CaLas affects citrus development and suppresses citrus disease resistance, comprehensively, in a complicated manner. Ubiquitin-mediated protein degradation might play a vital role in CaLas virulence. Deep characterization of the interactions between the identified virulence factors and their prey will shed light on HLB. Eventually, it will help in developing HLB-resistant citrus and save the endangered citrus industry worldwide.

Recurrent water deficit causes alterations in the profile of redox proteins in citrus plants

Plant acclimation to recurrent stress involves profound alterations in multiple genetic, metabolic and physiological processes. Stressful conditions usually implicate imbalance in reactive oxygen species (ROS) production and removal rates, which may lead to oxidative stress. However, the primary cellular targets of oxidative stress and their relevance in plant acclimation to abiotic stresses remains poorly characterized. By comparing redox proteomic and sugar profiles in citrus Valencia (VO) scions grafted onto two rootstocks with different soil water extraction capacities - Rangpur Lime (RL) and Sunki Maravilha (SM) - here we demonstrate that both ROS-mediated post-translational protein modification and changes in sugar composition are associated with acclimation to recurrent drought in citrus. The redox proteomic analysis of the distinct scion/rootstock combinations exposed to one (WD1), two (WD2) or three (WD3) water deficit episodes revealed a total of 32 and 55 redox protein spots present in VO/RL and VO/SM plants, respectively. Mass spectrometry analysis of these protein spots revealed essential targets of ROS-mediated posttranslational protein modification in citrus plants challenged by recurrent drought. The oxidation of cysteine thiol groups into glyceraldehyde 3-phosphate dehydrogenase (GAPDH) was shown to increase in WD3 samples of the VO/RL combination, whereas the opposite was observed for the VO/SM combination. Similarly, recurrent drought promoted the oxidation of catalase thiol groups in VO/SM, but not in VO/RL. Carbohydrate profiling revealed that glucose, fructose and galactose may also contribute to the phenotypic differences observed between the citrus genotypes exposed to drought. These findings reveal for the first time that recurrent drought differentially affects the profile of redox proteomics of citrus, suggesting that this alteration may be part of the stress memory in perennial plants.