Molecular and functional characterization of Arabidopsis thaliana VPNB1 gene involved in plant vascular development.

Armadillo (ARM) repeat containing proteins constitute a large family in plants and are involved in diverse cellular functions, like signal transduction, proliferation and differentiation. In animals, ARM repeat proteins have been implicated in cancer development. In this study, we aimed in characterizing the VPNB1 gene from Arabidopsis thaliana and its role in plant development, by implementing a number of genetic and molecular approaches. AtVPNB1 encodes for an ARM repeat protein of unknown function, exclusively expressed in the cambium as well as in the differentiating xylem and phloem cells of the vascular system. Subcellular localization experiments showed that VPNB is confined in nucleoplasmic speckle-like structures unrelated to cajal bodies. Transgenic VPNB-impaired plants exhibit a slower growing phenotype and a non-canonical pattern of xylem tissue. On the contrary, VPNB overexpression lines display an inverted phenotype of increased growth, accompanied by an increased deposition of phloem and xylem cell layers. In line with the above data, qPCR analysis revealed a deregulation of several key master genes of secondary wall biosynthesis, underlining the involvement of VPNB1 in the regulation and differentiation of the root and shoot vascular tissue.

APRF1 promotes flowering under long days in Arabidopsis thaliana.

Arabidopsis thaliana flowering time mutants revealed the function of numerous genes that regulate the transition from vegetative to reproductive growth. Analyses of their loci have shown that many of them act as chromatin modifiers. In this study, a combination of molecular and genetic approaches have been implemented, to characterize the function of APRF1 (ANTHESIS POMOTING FACTOR 1) gene in A. thaliana and to investigate its role in plant development. APRF1 encodes for a low molecular weight nuclear WDR protein which displays functional homology to the Swd2 protein, an essential subunit of the yeast histone methylation COMPASS complex. Compared to WT plants, total loss-of-function aprf1 mutants exhibited shoot apical meristem (SAM) alterations and increased growth rates. However, the vegetative phase of aprf1 plants was prolonged and bolting was delayed, indicating an impairment in flowering under long days (LD). On the contrary, overexpression of APRF1 accelerates flowering. Consistent with the late flowering phenotype, the molecular data confirmed that FLC and SOC1 expression were significantly altered in the aprf1 mutants. Our data suggest that APRF1 acts upstream of FLC and promotes flowering under LD.