The Arabidopsis LAZY1 Family Plays a Key Role in Gravity Signaling within Statocytes and in Branch Angle Control of Roots and Shoots.

During gravitropism, the directional signal of gravity is perceived by gravity-sensing cells called statocytes, leading to asymmetric distribution of auxin in the responding organs. To identify the genes involved in gravity signaling in statocytes, we performed transcriptome analyses of statocyte-deficient Arabidopsis thaliana mutants and found two candidates from the LAZY1 family, AtLAZY1/LAZY1-LIKE1 (LZY1) and AtDRO3/AtNGR1/LZY2 We showed that LZY1, LZY2, and a paralog AtDRO1/AtNGR2/LZY3 are redundantly involved in gravitropism of the inflorescence stem, hypocotyl, and root. Mutations of LZY genes affected early processes in gravity signal transduction without affecting amyloplast sedimentation. Statocyte-specific expression of LZY genes rescued the mutant phenotype, suggesting that LZY genes mediate gravity signaling in statocytes downstream of amyloplast displacement, leading to the generation of asymmetric auxin distribution in gravity-responding organs. We also found that lzy mutations reversed the growth angle of lateral branches and roots. Moreover, expression of the conserved C-terminal region of LZY proteins also reversed the growth direction of primary roots in the lzy mutant background. In lateral root tips of lzy multiple mutants, asymmetric distribution of PIN3 and auxin response were reversed, suggesting that LZY genes regulate the direction of polar auxin transport in response to gravity through the control of asymmetric PIN3 expression in the root cap columella.

[Posterior encephalopathy syndrome in two patients after cancer surgery with transfusion].

We here report two patients (58-year-old, 77-year-old women) who presented themselves with generalized convulsion, impaired consciousness and hypertension several days after cancer surgery and transfusion. MRI T2 weighted images show an extensive area of increased signal intensity along the occipital cortex, but the underlying white matter revealed slight high signal intensity on diffusion weighted images. Despite similarities of those two cases to posterior leukoencephalopathy syndrome, they differ since the neuroimaging abnormalities are mostly in the occipital cortex. It is likely that the posterior cerebral cortex and white matter are vulnerable to circulatory, vascular and metabolic/toxic impairments. Depending on the abnormalities of many physiological variables, either the subcortical white matter, cortical gray or both might become a major target of this syndrome.