LS-2-O-3517 Autophagic hallmarks and gene expression accompany programmed cell death in stress-induced pollen embryogenesis and pollen development

The microspore or immature pollen grain follows in vivo the gametophytic program and differentiates to form the mature pollen. At defined stages, the tapetum, anther tissue with a key nursing role during microspore development, undergoes programmed cell death (PCD). In vitro, upon the application of a stress treatment the microspore can be deviated towards embryogenesis leading to plant regeneration, the so-called microspore embryogenesis, a process which represents an important tool in plant breeding to obtain double-haploid plants; <span> the efficiency of the process is affected by cell death of microspores after the stress. Plant programmed cell death (PCD) seems to share some features with both apoptosis and autophagy in animals; nevertheless, recent data on PCD in plants indicate that classification is not clear yet. Increasing evidences indicate that autophagy plays critical roles in both PCD processes, during development and stress responses.

In this work we studied the existence and dynamics of autophagy compartments, machinery and genes, specifically Beclin1/ATG6 and ATG8, in relation to ROS/RNS production, caspase-like activity and ultrastructural rearrangements during two PCD processes of the pollen pathways,: the PCD of microspores in culture after the stress treatment inducing embryogenesis, and the PCD of tapetum during pollen development, in Brassica napus and Hordeum vulgare, by a multidisciplinary approach.

Early after microspore embryogenesis induction by stress treatments, cell death increased together with ROS and NO production, caspase 3-like activity and Beclin1/ATG6 gene expression induction. During pollen development, in tapetal cells at PCD initiation, apoptotic-like features as nuclear condensation, cytochrome C release and high caspase 3-like activity were detected concomitantly with an increase of vesicles, vacuoles and different autophagic-like structures in the cytoplasms, some of them were labelled by ATG8.

Results will be discussed on the light of the participation of autophagy in the PCD during the two pollen developmental pathways.

Rodríguez-Serrano M, Bárány I, Prem D, Coronado MJ, Risueño MC, Testillano PS (2012) NO, ROS and cell death associated with caspase-like activity increase in stress-induced microspore embryogenesis of barley. J. Exp. Botany, 63, 2007-2024.

Solís MT, Chakrabarti N, Corredor E, Cortés-Eslava J, Rodríguez-Serrano M, Biggiogera M, Risueño MC, Testillano PS (2014) Epigenetic changes accompany developmental programmed cell death in tapetum cells. Plant Cell Physiol. 55, 16-29.