2017 ASHS Annual Conference

Abiotic stresses reduce the visual quality of ornamental plants and consequently cause economic losses for growers. Plant responses to stress involve several physiological, morphological, and molecular changes. Autophagy, a process of cellular degradation, is important for normal plant development and stress responses. During autophagy, double membrane structures (autophagosomes) capture the cytosolic contents and deliver them to the vacuole. Autophagosome formation is regulated by the autophagy-related (ATG) genes. Here, we describe how the ATG genes of Petunia xhybrida (PhAtg4, PhAtg5, PhAtg6, PhAtg7, PhAtg8a, and PhAtg13) are regulated in response to low fertility and salinity stress. During low fertility stress, upregulation of the ATG genes was accompanied by a decrease in leaf chlorophyll content. In contrast, under salinity stress the ATG genes were either downregulated or not affected even when significant changes were observed in stomatal conductance, leaf temperature, photosystem II efficiency, and electrolyte leakage. To further investigate autophagy, wild type petunia and transgenic RNAi lines targeting endogenous PhAtg6 were grown for six weeks using three irrigation solutions: control (100 ppm N from 15-5-15), low fertility (10 ppm N from 15-5-15), and salinity (100 ppm N from 15-5-15, 80mM NaCl). Growth index (GI), dry weight (DW), days to flower anthesis (DF), number of leaves per plant (LP), leaf area (LA), and chlorophyll content (SPAD) were measured to evaluate the stress responses in wild type and transgenic petunias. Under control conditions, transgenic lines showed lower SPAD values, delayed flowering, a reduction in number of leaves per plant, and an increase in leaf area. Low fertility stress did not affect GI, LP, and LA; however, DW and leaf chlorophyll content were higher in transgenic plants. Salinity treatment reduced growth and leaf area, but not the number of leaves in transgenic lines. Although the autophagy molecular machinery was activated in response to the low fertility treatment, salinity stress did not have the same effect. Disruption of PhAtg6 expression affected normal development of petunia and its ability to tolerate low fertility and salinity stress. By identifying the function of the autophagy related genes, we aim to increase our understanding of plant development and abiotic stress tolerance.