Gibberellins producing endophytic Aspergillus nidulans DSE-2 biosorbs Cd and down-regulates OsNRAMP5 and OsCd1 genes to improve rice growth in contaminated soil

Abstract

Cadmium tolerant endophytic fungi were isolated from Amaranthus spinosus L. roots. The isolates were screened for gibberellins (GAs) secretion and Cd stress alleviation in rice seedlings. Among the isolates, DSE-2 was selected for its ability to release GAs and alleviate Cd stress in the seedlings. The isolate was identified to be Aspergillus nidulans. When inoculated on rice seedlings, DSE-2 enhanced their relative growth rate and net assimilation rate by 115% and 56.4% compared to the control. Presence of Cd in the soil reduced RGR and NAR to 41 and 68.4 % of the control. However, DSE-2 associated rice seedlings were not affected by the stress, indicating that the inoculant was effective in alleviating Cd stress. When the DSE-2 inoculaed seedlings were treated with GAs inhibitor, uniconazole, efficiency of the inoculant was severely impaired. Expression of the genes involved in Cd uptake (OsNRAMP5 and OsCd1) was significantly reduced in DSE-2 inoculated seedlings compared to the control. However, uniconazole treated seedlings had higher expression of these genes, indicating the involvement of GAs in Cd stress alleviation by the endophyte. This was further supported by the lower accumulation of Cd in endophyte associated seedlings and higher accumulation of Cd in uniconazole treated endophyte associated seedlings. Accumulation of ROS followed an opposite trend, lower in endophyte associated seedlings than those receiving uniconazole. Our results indicate that fungal GAs are important in reducing Cd uptake by rice seedlings accompanied by lower level of ROS.