Phylogenetic relationships among five species of Armeniaca Scop. (Rosaceae) using microsatellites (SSRs) and capillary electrophoresis

The genus Armeniaca Scop. is well known for its popular cultivated edible fruit trees such as Armeniaca vul- garis Lam. and ornamental flowers such as A. mume Sieb. Another species, A. cathayana Fu et al., one of six important dry fruits （kernel-using apricot）, is cultivated for its edible seeds in North China. In the present study, DNA from 70 individuals of A rmeniaca, including 38 of A. cathayana, 18 ofA. vulgaris, 12 ofA. sibirica, 1 ofA. dasycarpa and 1 of A. mume, was extracted and analyzed using microsatellites and capillary electrophoresis. For 20 polymorphic loci selected, 339 alleles and 140.7 effective alleles were detected. The number of alleles per locus ranged from 8 to 28, with an average of 16.95 alleles per locus. The observed heterozygosity （Ho） and the expected heterozygosity （He） ranged from 0.427 to 0.971 and from 0.737 to 0.912, respectively. The polymorphism information content varied from 0.708 to0.905, with an average of 0.827. Based on the genetic similarity among 70 individuals, a UPGMA was used to establish the phylogenetic relationships. The taxonomic positions among five species were clearly revealed, and A. cathayana was more closely related to A. vulgaris than to A. sibirica. The results will provide a scientific basis for research on the taxonomy, germplasm resources and breeding ofArmeniaca, especially for A. cathayana.

Calcium-dependent protein kinases CPK21 and CPK23 phosphorylate and activate the iron-regulated transporter IRT1 to regulate iron deficiency in Arabidopsis

Iron(Fe)is an essential micronutrient for all organisms.Fe availability in the soil is usually much lower than that required for plant growth,and Fe deficiencies seriously restrict crop growth and yield.Calcium(Ca2+)is a second messenger in all eukaryotes;however,it remains largely unknown how Ca2+regulates Fe deficiency.In this study,mutations in CPK21 and CPK23,which are two highly homologous calcium-dependent protein kinases,conferredimpaired growth and rootdevelopment under Fe-deficient conditions,whereas constitutively active CPK21 and CPK23 enhanced plant tolerance to Fe-deficient conditions.Furthermore,we found that CPK21 and CPK23 interacted with and phosphorylated the Fe transporter IRONREGULATED TRANSPORTER1(IRT1)at the Ser149 residue.Biochemical analyses and complementation of Fe transport in yeast and plants indicated that IRT1 Ser149 is critical for IRT1 transport activity.Taken together,these findings suggest that the CPK21/23-IRT1 signaling pathway is critical for Fe homeostasis in plants and provides targets for improving Fe-deficient environments and breeding crops resistant to Fe-deficient conditions.

Tonoplast-associated calcium signaling regulates manganese homeostasis in Arabidopsis

Manganese(Mn)is an essential micronutrient in plants.However,excessive Mn absorption in acidic and waterlogged soils can lead to Mn toxicity.Despite their essential roles in Mn homeostasis,transcriptional and post-transcriptional modifications of Mn transporters remain poorly understood.Here,we demonstrated that high-Mn stress induces an obvious Ca^(2+) signature in Arabidopsis.We identified four calcium-dependent protein kinases,CPK4/5/6/11,that interact with the tonoplast-localized Mn and iron(Fe)transporter MTP8 in vitro and in vivo.The cpk4/5/6/11 quadruple mutant displayed a dramatic high-Mn-sensitive phenotype similar to that of the mtp8 mutant.CPKs phosphorylated the N-terminal domain of MTP8 primarily at the Ser31 and Ser32 residues.Transport assays combined with multiple physiological experiments on phospho-dead variant MTP8^(S31/32A)and phospho-mimetic variant MTP8^(S31/32D)plants under different Mn and Fe conditions suggested that Ser31 and Ser32 are crucial for MTP8 function.In addition,genetic analysis showed that CPKs functioned upstream of MTP8.In summary,we identified a tonoplast-associated calcium signaling cascade that orchestrates Mn homeostasis and links Mn toxicity,Ca^(2+) signaling,and Mn transporters.These findings provide new insight into Mn homeostasis mechanisms and Ca^(2+) signaling pathways in plants,providing potential targets for engineering heavy metal toxicity-tolerant plants.

Ca^(2+)-dependent successive phosphorylation of vacuolar transporter MTP8 by CBL2/3-CIPK3/9/26 and CPK5 is critical for manganese homeostasis in Arabidopsis

Manganese(Mn)is an essential micronutrient for all living organisms.However,excess Mn supply that can occur in acid or waterlogged soils has toxic effects on plant physiology and development.Although a variety of Mn transporter families have been characterized,we have only a rudimentary understanding of how these transporters are regulated to uphold and adjust Mn homeostasis in plants.Here,we demonstrate that two calcineurin-B-like proteins,CBL2/3,and their interacting kinases,CIPK3/9/26,are key regulators of plant Mn homeostasis.Arabidopsis mutants lacking CBL2 and 3 or their interacting protein kinases CIPK3/9/26 exhibit remarkably high Mn tolerance.Intriguingly,CIPK3/9/26 interact with and phosphorylate the tonoplast-localized Mn and iron(Fe)transporter MTP8 primarily at Ser35,which is conserved among MTP8 proteins from various species.Mn transport complementation assays in yeast combined with multiple physiological assays indicate that CBL-CIPK-mediated phosphorylation of MTP8 negatively regulates its transport activity from the cytoplasm to the vacuole.Moreover,we show that sequential phosphorylation of MTP8,initially at Ser31/32 by the calcium-dependent protein kinase CPK5 and subsequently at Ser35 by CIPK26,provides an activation/deactivation fine-tuning mechanism for differential regulation of Mn transport.Collectively,our findings define a two-tiered calcium-controlled mechanism for dynamic regulation of Mn homeostasis under conditions of fluctuating Mn supply.