A role for the Auxin Response Factors ARF6 and ARF8 homologs in petal spur elongation and nectary maturation in Aquilegia

The petal spur of the basal eudicotAquilegiais a key innovation associated with the adaptive radiation of the genus. Previous studies have shown that diversification ofAquilegiaspur length can be predominantly attributed to variation in cell elongation. However, the genetic pathways that control the development of petal spurs are still being investigated. Here, we focus on a pair of closely related homologs of the AUXIN RESPONSE FACTOR family,AqARF6andAqARF8, to explore their roles inAquileiga coeruleapetal spur development. Expression analyses of the two genes show that they are broadly expressed in vegetative and floral organs, but have relatively higher expression in petal spurs, particularly at later stages. Knockdown of the twoAqARF6andAqARF8transcripts using virus-induced gene silencing resulted in largely petal-specific defects, including a significant reduction in spur length due to a decrease in cell elongation. These spurs also exhibited an absence of nectar production, which was correlated with downregulation ofSTYLISHhomologs that have previously been shown to control nectary development. This study provides the first evidence ofARF6/8homolog-mediated petal development outside the core eudicots. The genes appear to be specifically required for cell elongation and nectary maturation in theAquilegiapetal spur

Dependence of the global dayside reconnection rate on interplanetary magnetic field By and the earth’s dipole tilt

Abstract In the recent years, significant attention has been given to the combined effect of Interplanetary Magnetic Field (IMF) duskward component (By) and dipole tilt on the global magnetosphere-ionosphere system response. Numerous studies have pointed out that when the Earth’s magnetic dipole is tilted away from the Sun (negative dipole tilt during northern winter), and IMF has a positive By component, the effects on ionospheric currents, particle precipitation, ionospheric convection, and average size of the auroral oval, is significantly more enhanced, compared to when IMF By is negative. Furthermore, this IMF By polarity effect reverses when Earth’s dipole is tilted in the opposite direction. The underlying cause has remained unclear. Our analysis shows that substorms tend to be stronger during the same IMF By and dipole tilt polarity combination. Taken together with earlier results showing also more frequent substorms during the same conditions, our observations suggests that when IMF By and dipole tilt have opposite signs, there is a more efficient global dayside reconnection rate. We also show analysis of the occurrence frequency of periods of Steady Magnetospheric Convection, substorm onset latitude, and the isotropic boundary of proton precipitation, that are all consistent with our conclusion that the combination of IMF By and dipole tilt polarity affect the global dayside reconnection rate