The Catharanthus roseus RLK1-like kinase (CrRLK1L) family is involved in multiple processes during plant growth. However, little is known about CrRLK1L in the wood of the pear fruit tree Pyrus bretchneideri. In this study, 26 CrRLK1L gene members were identified in pear and were grouped into six subfamilies according to phylogenetic analyses. Evolutionary analysis indicated that recent whole genome duplication (WGD) and dispersed gene duplications may contribute to the expansion of the CrRLK1L gene family in pear. Moreover, tissue-specific expression analyses suggested that CrRLK1Ls are involved in the development of various pear tissues. Subsequent qRT-PCR analyses indicated that CrRLK1Ls might play important roles in pollen tube growth. Finally, experiments with antisense oligonucleotides (ASO) demonstrated that PbrCrRLK1L26 have functions in pollen tube elongation and that PbrCrRLK1L3 regulates pollen tube rupture. These results will be useful for elaborating the biological roles of CrRLK1Ls in pear growth and development.
S-type anion channels (SLAC/SLAHs), which play important roles in plant anion (such as nitrate and chloride) transport, growth and development, abiotic stress responses and hormone signaling. However, there is far less information about this family in Rosaceae species. We performed a genome-wide analysis and identified SLAC/SLAH gene family members in pear (Pyrus bretschneideri) and four other species of Rosaceae (Malus domestica, Prunus persica, Fragaria vesca and Prunus mume). A total of 21 SLAC/SLAH genes were identified from the five Rosaceae species. Based on the structural characteristics and a phylogenetic analysis of these genes, the SLAC/SLAH gene family could be classified into three main groups (I, II and III). The
Theanine (N-ethyl-γ-l-glutamine) is a special nonprotein
amino acid that contributes to the umami taste and health function
of tea. Although recent studies on tea breeding have focused on albino
tea because of its umami taste, a factor of higher theanine concentration,
the mechanism of biosynthesis of l-theanine is still unclear.
In this study, four glutamine synthetase genes (CsGSs) were obtained and functionally characterized by overexpressing
them in Arabidopsis. The enzyme activities
of the purified CsGS proteins from Escherichia coli were detected. The results showed that CsGSs have a dual function
in the synthesis of glutamine and theanine in vivo and in vitro. Interestingly, l-theanine was abundantly synthesized in the tender shoots of
“Huabai 1”. In the white tender shoots, the cytosol CsGS1.2 might exhibit increased expression to compensate
for decreasing levels of chloroplast CsGS2, which
plays a vital role in high accumulation of theanine in “Huabai
1”. In addition, CsGS2 was most likely the
key l-theanine synthases in green tissues of tea. The present
findings will provide basis for and considerably broaden the scope
of understanding the function of CsGSs and the mechanism
of l-theanine accumulation in the tender shoots of “Huabai
1”, and will be useful for breeding and screening tea with
high l-theanine content.
Rapid alkalinization factors (RALFs) are cysteine-rich peptides that play important roles in a variety of biological processes, such as cell elongation and immune signaling. Recent studies in Arabidopsis have shown that RALFs regulate pollen tube growth via plasma membrane receptor-like kinases (RLKs). However, the downstream signal transduction mechanisms of RLKs in pollen tubes are unknown. Here, we identified PbrRALF2, a pear (Pyrus bretschneideri) pollen RALF peptide that inhibits pollen tube growth. We found that PbrRALF2 interacts with a malectin-like domain-containing RLK, PbrCrRLK1L13. The relative affinity between PbrRALF2 and PbrCrRLK1L13 was at the submicromolar level, which is consistent with the values of ligand–receptor kinase pairs and the physiological concentration for PbrRALF2-mediated inhibition of pollen tube growth. After binding to its extracellular domain, PbrRALF2 activated the phosphorylation of PbrCrRLK1L13 in a dose-dependent manner. We further showed that the MAP kinase PbrMPK18 is a downstream target of PbrCrRLK1L13 that mediates PbrRALF2-elicited reactive oxygen species (ROS) production. The excessive accumulation of ROS inhibits pollen tube growth. We show that MPK acts as a mediator for CrRLK1L to stimulate ROS production, which might represent a general mechanism by which RALF and CrRLK1L function in signaling pathways.
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