Cattle tick; Entomopathogenic fungi; Abiotic factors

Metarhizium spp. is one of the most used entomopathogenic fungi to control agricultural pests and also presents positive results in tests against ticks, especially Rhipicephalus microplus. However, these agents can be negatively affected by biotic and abiotic factors, such as solar irradiation, especially the UV-B fraction, which causes serious damage to fungi, decreasing their effectiveness in controlling pests. Thus, this work analyzed the M. pingshaense isolate LCM S10 with the objective of: 1) verifying the UV tolerance of conidia, blastospores and microsclerotia of the isolate LCM S10; 2) to evaluate the survival of engorged females of R. microplus treated with M. pingshaense blastospores and exposed to UV-B radiation for three consecutive days (total daily fluency of 4.0 kJ/m²); 3) analyze the transcriptoma of the M. pingshaense isolate LCM S10 after being exposed to UV-B radiation. The propagules (conidia, blastospores and microsclerotia) were exposed to UV-B radiation with a total fluency of 4.0 kJ/m². Conidia were evaluated for germination 24h after exposure to UV-B. Microsclerotia and blastospores were evaluated for the presence of colony forming units (CFU) 24 and 72h after exposure to UV-B, respectively. All three propagules demonstrated high tolerance to ultraviolet radiation. The bioassay to verify the mortality of engorged females of R. microplus, as well as the analysis of the biological parameters, showed that there was no statistical difference between the control and the group of females treated with blastospores and exposed to UV-B for three consecutive days (total fluency daily of 4.0 kJ/m²), proving that ultraviolet radiation damages fungal propagules. Regarding female survival, there was a statistical difference and females in the group treated with blastospores and not exposed to UV-B survived, on average, 12 days, while females treated with blastospores and exposed to ultraviolet radiation for three consecutive days had a median survival of 18.5 days. All females in the control group had a mean survival of 23 days. To understand how UV-B light regulates gene expression in M. pingshaense blastospores, we performed a transcriptional analysis, where differential expression analysis identified 728 genes differentially expressed, 320 genes induced and 408 genes suppressed in the presence of UV-B. The functional categories where the genes that were most suppressed are: transport and metabolism of aminoacids; transport and metabolism of carbohydrates; and post-translational modification, proteins turnover and chaperones. The functional categories where the most induced genes are found are: biosynthesis, transport and catabolism of secondary metabolites; transport and metabolism of coenzymes; and post-translational modification, proteins turnover and chaperones. Data on the UV-B tolerance of a fungal isolate reveal important information about its intrinsic tolerance. This is the first work analyzing the blastospore transcriptoma of M. pingshaense when exposed to UV-B. This study aims to help future research on the discovery of fungal isolates and promising propagules for biological control.