Transcriptional Profile of Sod Genes in Sunflower under Broomrape Stress

Maria Duca, Angela Port, Steliana Clapco, Ana Mutu

Center of Functional Genetics, Moldova State University, Chişinău

Keywords: sunflower, broomrape, Orobanche cumana, pre-attachment, superoxide dismutases, genes.

Abstract: Sunflower broomrape (Orobanche cumana Wallr.) is an obligate, chlorophyll-lacking root parasite and one of the most destructive pathogens of sunflower in Eastern Europe and the Mediterranean region, including the Republic of Moldova. The continuous emergence of new, more virulent races following the cultivation of monogenic resistant varieties (Or1-Or7) has shifted research focus toward understanding non-specific, quantitative polygenic resistance mechanisms.
Reactive oxygen species (ROS) are inevitable byproducts of cellular metabolism that function both as signaling molecules and as mediators of oxidative damage during plant stress responses. Superoxide dismutases (SODs) represent the first enzymatic defense against ROS, catalyzing the dismutation of superoxide radicals into hydrogen peroxide and molecular oxygen. Despite their essential role, the transcriptional regulation of SOD genes during the early stages of broomrape infection remains largely unexplored.
This study aimed to investigate the expression dynamics of SOD-encoding genes in the roots of three sunflower F₁ hybrids - Favorit and P64LE20 (resistant) and Performer (susceptible) - during the pre-attachment phase of O. cumana infection. Plants were exposed to germinated broomrape seeds and sampled at 2, 6, 12, and 24 h post-inoculation. Gene expression levels were analyzed using quantitative real-time PCR.
Comparative analysis of SOD gene expression revealed distinct patterns between resistant and susceptible sunflower hybrids. In the absence of biotic stress, transcriptional activity followed the pattern Cu/Zn-SOD II > Cu/Zn-SOD I > Mn-SOD II > Mn-SOD I, with more pronounced variations in the susceptible Performer. Upon infection, the resistant Favorit showed rapid, oscillating up- and down-regulation of Mn-SOD I, Mn-SOD II, and Cu/Zn-SOD II during the first 12 hours, stabilizing by 24 hours, reflecting fine-tuned early redox control. P64LE25 exhibited a gradual and sustained activation, particularly of Mn-SOD I and Cu/Zn-SOD II, indicative of a delayed but stable oxidative homeostasis. In contrast, the susceptible Performer displayed moderate early activation followed by strong repression of Cu/Zn-SOD isoforms, culminating in a marked reduction of Cu/Zn-SOD II at 24 h, signaling transcriptional loss of control and oxidative overload.
The results provide a molecular basis for the use of SOD genes as early markers of resistance to Orobanche cumana infestation. Differential expression profiles can be integrated into marker-assisted breeding programs, facilitating the early identification of tolerant genotypes and accelerating the development of resistant sunflower cultivars.

Acknowledgments: This study was supported by the subprogramme 011101 Genetic and biotechnological approaches to the management of agroecosystems in the conditions of climate change, funded by the Ministry of Education and Research.