CaLecRK-S.5, a pepper L-type lectin receptor kinase gene, accelerates Phytophthora elicitin-mediated defense response

Polyphenol oxidases regulate pollen development through modulating flavonoids homeostasis in tobacco

Pollen development is critical in plant reproduction. Polyphenol oxidases (PPOs) genes encode defense-related enzymes, but the role of PPOs in pollen development remains largely unexplored. Here, we characterized NtPPO genes, and then investigated their function in pollen via creating NtPPO9/10 double knockout mutant (cas-1), overexpression 35S::NtPPO10 (cosp) line and RNAi lines against all NtPPOs in Nicotiana tabacum. NtPPOs were abundantly expressed in the anther and pollen (especially NtPPO9/10). The pollen germination, polarity ratio and fruit weights were significantly reduced in the NtPPO-RNAi and cosp lines, while they were normal in cas-1 likely due to compensation by other NtPPO isoforms. Comparisons of metabolites and transcripts between the pollen of WT and NtPPO-RNAi, or cosp showed that decreased enzymatic activity of NtPPOs led to hyper-accumulation of flavonoids. This accumulation might reduce the content of ROS. Ca²⁺ and actin levels also decreased in pollen of the transgenic lines.Thus, the NtPPOs regulate pollen germination through the flavonoid homeostasis and ROS signal pathway. This finding provides novel insights into the native physiological functions of PPOs in pollen during reproduction.

The enhanced Valsa canker resistance conferred by MdLecRK-S.4.3 in Pyrus betulifolia can be largely suppressed by PbePUB36

L-type lectin receptor-like kinases (L-LecRKs) act as a sensor of extracellular signals and an initiator for plant immune responses. However, the function of LecRK-S.4 on plant immunity has not been extensively investigated. At present, in the apple (Malus domestica) genome, we identified that MdLecRK-S.4.3, a homologous gene of LecRK-S.4, was differentially expressed during the occursion of Valsa canker. Over-expression of MdLecRK-S.4.3 facilitated the induction of immune response and enhanced the Valsa canker resistance of apple and pear fruit, and 'Duli-G03' (Pyrus betulifolia) suspension cells. On the contrary, the expression of PbePUB36, RLCK XI subfamily member, was significantly repressed in the MdLecRK-S.4.3 overexpressed cell lines. Over-expression of PbePUB36 interfered with the Valsa canker resistance and immune response caused by up-regulation of MdLecRK-S.4.3. Furthermore, MdLecRK-S.4.3 interacted with BAK1 or PbePUB36 in vivo. In conclusion, MdLecRK-S.4.3 activated various immune responses and positively regulate Valsa canker resistance, which could be largely compromised by PbePUB36. MdLecRK-S.4.3 interacted with PbePUB36 and/or MdBAK1 to mediate the immune responses. This finding provides a reference for studying the molecular mechanism of resistance to Valsa canker and resistance breeding.

Plant lectins: Handymen at the cell surface

Lectins are carbohydrate-binding proteins and are involved in a multitude of biological functions. Lectins at the surface of plant cells often occur as lectin receptor-like kinases (LecRLK) anchored to the plasma membrane. These LecRLKs are part of the plant's pattern-recognition receptor (PRR) system enabling the plant to perceive threats and respond adequately. Furthermore, plant lectins also occur as secreted proteins, which are associated with stress signalling and defence. The aim of this short review is to provide a general perspective on plant lectins and their role at the cell surface.

Potato StLecRK-IV.1 negatively regulates late blight resistance by affecting the stability of a positive regulator StTET8

Plant receptor-like kinases (RLKs) regulate many processes in plants. Many RLKs perform significant roles in plant immunity. Lectin receptor-like kinases (LecRLKs) are a large family of RLKs. However, the function of most of LecRLKs is poorly understood. In this study, we show that a potato LecRLK, StLecRK-IV.1, is involved in plant immunity against Phytophthora infestans. As a negative regulator of immunity, StLecRK-IV.1 is down-regulated by P. infestans and activated by abscisic acid (ABA). The transient expression of StLecRK-IV.1 in Nicotiana benthamiana enhanced P. infestans leaf colonization significantly. In contrast, the disease lesion size caused by P. infestans was reduced in Virus-induced gene silencing (VIGS) of StLecRK-IV.1 orthologue in N. benthamiana, NbLecRK-IV.1, as well as in potato plants with stable RNA interference of StLecRK-IV.1. Tetraspanin-8 (StTET8) was identified to be interacting with StLecRK-IV.1 using a membrane yeast-2-hybrid system, which was further verified by co-immunoprecipitation, a luciferase complementation assay, and a bimolecular fluorescence complementary (BiFC) test. StTET8 is a positive immune regulator that restrains P. infestans infection. The co-expression of StLecRK-IV.1 with StTET8 antagonized the positive roles of StTET8 against P. infestans. Moreover, the co-expression of StTET8 with StLecRK-IV.1 affected the stability of StTET8, which was confirmed by a Western blot assay and confocal assay. Taken together, our work firstly revealed that a potato L-type Lectin RLK, StLecRK-IV.1, negatively regulates plant immunity by targeting a positive regulator, StTET8, through affecting its stability.

Lectin receptor-like kinase LecRK-VIII.2 is a missing link in MAPK signaling-mediated yield control

The energy allocation for vegetative and reproductive growth is regulated by developmental signals and environmental cues, which subsequently affects seed output. However, the molecular mechanism underlying how plants coordinate yield-related traits to control yield in changing source-sink relationships remains largely unknown. Here, we discovered the lectin receptor-like kinase LecRK-VIII.2 as a specific receptor-like kinase that coordinates silique number, seed size, and seed number to determine seed yield in Arabidopsis (Arabidopsis thaliana). The lecrk-VIII.2 mutants develop smaller seeds, but more siliques and seeds, leading to increased yield. In contrast, the plants overexpressing LecRK-VIII.2 form bigger seeds, but less siliques and seeds, which results in similar yield to that of wild-type plants. Interestingly, LecRK-VIII.2 promotes the growth of the rosette, root, and stem by coordinating the source-sink relationship. Additionally, LecRK-VIII.2 positively regulates cell expansion and proliferation in the seed coat, and maternally controls seed size. The genetic and biochemical analyses demonstrated that LecRK-VIII.2 acts upstream of the mitogen-activated protein kinase (MAPK) gene MPK6 to regulate silique number, seed size, and seed number. Collectively, these findings uncover LecRK-VIII.2 as an upstream component of the MAPK signaling pathway to control yield-related traits and suggest its potential for crop improvement aimed at developing plants with stable yield, a robust root system, and improved lodging resistance.

Identification of LecRLK gene family in Cerasus humilis through genomic-transcriptomic data mining and expression analyses

Lectin receptor-like protein kinases (LecRLKs) have been shown to be involved in plants’ responses to various biotic and abiotic stresse factors. Cerasus humilis is an important fruit species widely planted for soil and water conservation in northern China due to its strong tolerance to drought and salinity stresses. In this study, a total of 170 LecRLK family genes (125 G-types, 43 L-types and 2 C-types) were identified in the newly released whole-genome sequences of C. humilis. Furthermore, nine representative LecRLK genes in young plants of C. humilis under varying drought and salinity stresses were selected for qRT-PCR analysis. Our systematic comparative analyses revealed the active participation of these nine LecRLK genes in the salt and drought stress responses of C. humilis. The results from our study have provided a solid foundation for future functional verification of these LecRLK family genes and will likely help facilitate the more rapid and effective development of new stress resistant Cerasus humilis cultivars.

Lectin Receptor-Like Kinases: The Sensor and Mediator at the Plant Cell Surface

Lectin receptor-like kinases (LecRLKs), a plant-specific receptor-like kinase (RLK) sub-family, have been recently found to play crucial roles in plant development and responses to abiotic and biotic stresses. In this review, we first describe the classification and structures of Lectin RLKs. Then we focus on the analysis of functions of LecRLKs in various biological processes and discuss the status of LecRLKs from the ligands they recognize, substrate they target, signaling pathways they are involved in, to the overall regulation of growth-defense tradeoffs. LecRLKs and the signaling components they interact with constitute recognition and protection systems at the plant cell surface contributing to the detection of environmental changes monitoring plant fitness.