Elucidating the immunity-pathogenesis nexus in rice and Helminthosporium oryzae: Insights from gene expression profiling and phytohormone analysis

Rice (Oryza sativa L.) is a major global staple food and a key crop in Pakistan, however, it is increasingly being threatened by climate change and biotic stresses such as brown leaf spot (BLS).We investigated the role of plant growth regulators in enhancing rice resistance to H. oryzae in four newly developed rice lines and one local variety for resistance to Helminthosporium oryzae by analyzing plant growth regulators and gene expression in young plants after pathogen attack.Salicylic acid (SA) levels in infected plants increased significantly, with the highest levels recorded at 48 hpi in V 3 , followed by V 1 .Abscisic acid (ABA) and jasmonic acid (JA) levels also increased post-infection, with V 3 showing the highest increase for both hormones.Additionally, the expression of defense marker genes OsWRKY24, -30, -45, and -53 was upregulated following infection.OsPR1, OsSIPK, OsPLDα1, and PPO, demonstrated heightened expression, with notable peaks in V 1 , V 3 , and V 4 .ET biosynthetic gene ACS2 alongside elevated SA corresponded with increased expression of PR1 and LOX3.Furthermore, OsERF3 levels significantly increased across all infected rice lines, particularly in V 3 , suggesting a coordinated defensive response.These results revealed that SA, along with specific defense-related genes, crucially mediates rice response to H. oryzae infection, with line V 3 showing the most robust resistance among the tested rice lines.Our findings support the fact that pathogens manipulate hormone signaling pathways and relative expression of genes to disrupt and evade plant defenses.