The Brown Midrib Leaf (bml) Mutation in Rice (Oryza sativa L.) Causes Premature Leaf Senescence and the Induction of Defense Responses

Abstract

Isolating and characterizing mutants with altered senescence phenotypes is one of the ways to understand the molecular basis of leaf aging. Using ethyl methane sulfonate mutagenesis, a new rice (Oryza sativa) mutant, brown midrib leaf (bml), was isolated from the indica cultivar ‘Zhenong34’. The bml mutants had brown midribs in their leaves and initiated senescence prematurely, at the onset of heading. The mutants had abnormal cells with degraded chloroplasts and contained less chlorophyll compared to the wild type (WT). The bml mutant showed excessive accumulation of reactive oxygen species (ROS), increased activities of superoxide dismutase, catalase, and malondialdehyde, upregulation of senescence-induced STAY-GREEN genes and senescence-related transcription factors, and down regulation of photosynthesis-related genes. The levels of abscisic acid (ABA) and jasmonic acid (JA) were increased in bml with the upregulation of some ABA and JA biosynthetic genes. In pathogen response, bml demonstrated higher resistance against Xanthomonas oryzae pv. oryzae and upregulation of four pathogenesis-related genes compared to the WT. A genetic study confirmed that the bml trait was caused by a single recessive nuclear gene (BML). A map-based cloning using insertion/deletion markers confirmed that BML was located in the 57.32kb interval between the L5IS7 and L5IS11 markers on the short arm of chromosome 5. A sequence analysis of the candidate region identified a 1 bp substitution (G to A) in the 5′-UTR (+98) of bml. BML is a candidate gene associated with leaf senescence, ROS regulation, and disease response, also involved in hormone signaling in rice. Therefore, this gene might be useful in marker-assisted backcrossing/gene editing to improve rice cultivars.

Loss function of SL (sekiguchi lesion) in the rice cultivar Minghui 86 leads to enhanced resistance to (hemi)biotrophic pathogens

“…After heating to 90–95 °C for 15 min, the leaves were transferred to a fresh destaining solution and shaked gently overnight. Trypan blue staining was carried out as previously described [ 56 ].…”

Abiotic Stresses Intervene with ABA Signaling to Induce Destructive Metabolic Pathways Leading to Death: Premature Leaf Senescence in Plants

“…In Arabidopsis At4G25080 , At5G54190 , At1G44446 , At3G51820 , PAO-encoded magnesium protoporphyrin IX methyltransferase, protochlorophyllide reductase, chlorophyllide-a oxygenase and bacteriochlorophyll a synthase affect Chl synthesis and leaf development [14,15,16,17,18]. In rice, pentatricopeptide repeat genes regulate the expression of chloroplast genes, resulting in leaf senescence [19], while exogenous ABA has been reported to increase the expression of SAGs [20,21,22].…”

Knocking Out the Gene RLS1 Induces Hypersensitivity to Oxidative Stress and Premature Leaf Senescence in Rice

“…Consistent with this, the abundance of SAG transcripts proved to be higher in rls1 than in WT ( Figure 8 ). The same applied for the SATF s OsWRKY23 , OsWRKY72 and OsNAC2 , all of which are known to be up-regulated during leaf senescence [ 9 , 20 , 29 ]: they were similarly each transcribed more strongly in rls1 than in WT ( Figure 9 ). The autophagy genes OsATG4b , OsATG8a and OsATG18b have also all been shown to be up-regulated during leaf senescence [ 20 ], and again they were all transcribed more abundantly in rls1 than in WT ( Figure 10 ).…”