Identification of a Novel Semi-Dominant Spotted-Leaf Mutant with Enhanced Resistance to Xanthomonas oryzae pv. oryzae in Rice

Abstract

Many spotted-leaf mutants show enhanced disease resistance to multiple pathogen attacks; however, the mechanisms are largely unknown. Here, we reported a novel semi-dominant spotted-leaf mutant 24 (spl24) obtained from an ethyl methane sulfonate (EMS)-induced IR64 mutant bank. spl24 developed tiny brown lesions on the leaf tip and spread down gradually to the leaf base as well as the sheath at the early heading stage. The performances of major agronomic traits such as the plant height, panicle length, number of panicles/plant, and 1000-grain weight were significantly altered in spl24 when compared to the wild-type IR64. Furthermore, spl24 exhibited a premature senescing phenotype with degeneration of nuclear acids, significantly reduced soluble protein content, increased level of malonaldehyde (MDA), and lowered activities of reactive oxygen species (ROS) scavenging enzymes. Disease evaluation indicated that spl24 showed enhanced resistance to multiple races of Xanthomonas oryzae pv. oryzae, the causal pathogen of bacterial leaf blight in rice, with elevated expression of pathogenesis-related genes, salicylic acid (SA) signaling pathway-associated genes revealed by real-time quantitative PCR and high-throughput RNA sequencing analysis. Genetic analysis and gene mapping indicated that the lesion mimic phenotype was controlled by a novel semi-dominant nuclear gene. The mutation, tentatively termed as OsSPL24, was in a 110 kb region flanked by markers Indel-33 and Indel-12 in chromosome 11. Together, our data suggest that spl24 is a novel lesion mimic mutant with enhanced innate immunity and would facilitate the isolation and functional characterization of the target gene.

Identification and characterization of a spotted-leaf mutant spl40 with enhanced bacterial blight resistance in rice

“…A number of lesion mimic mutants show light-dependent initiation of lesions (Huang et al 2010; Chen et al 2018). To determine the effect of light on lesion initiation of spl40 , a second leaf from both WT and spl40 was covered with 2–3 cm aluminium foil for 7 days at the tillering stage.…”

“…The mutation was controlled by a single nuclear recessive gene located on the long arm of chromosome 5. In rice, a number of spotted-leaf mutants are affected in agronomic as well as physiological processes/traits (Huang et al 2011; Feng et al 2013; Chen et al 2018). For example, Spl24 , was affected in major physiological and agronomic traits like photosynthetic pigment content, plant height, seed setting rate and 1000-grain weight (Chen et al 2018).…”

“…In rice, a number of spotted-leaf mutants are affected in agronomic as well as physiological processes/traits (Huang et al 2011; Feng et al 2013; Chen et al 2018). For example, Spl24 , was affected in major physiological and agronomic traits like photosynthetic pigment content, plant height, seed setting rate and 1000-grain weight (Chen et al 2018). Similar to this, spl40 mutant showed decrease in photosynthetic pigment content and content of soluble protein, as well as decrease in important agronomic parameters like number of filled grains per panicle, number of panicle per plant, seed setting rate and 1000-grain weight.…”

“…The rice LIL1 mutant shows remarkable decrease in lesions when the light was intercepted by covering the leaf with aluminium foil (Zhou et al 2017). Similarly, both rice Spl24 and HM47 spotted-leaf mutants also exhibit light-induced formation of lesions under natural light conditions (Feng et al 2013; Chen et al 2018). In spl40 , lesion development was suppressed in the absence of light and appeared again when the light was re-instated.…”

Interaction of the Xanthomonas effectors XopQ and XopX results in induction of rice immune responses

“…A total of 5 µg RNA was reverse transcribed into cDNA using EcoDry™ Premix (Clontech, Mountain View, CA, USA) according to the manufacturer’s instructions. Quantitative real‐time RT‐qPCR of defence genes was performed with 5 × diluted cDNA using the gene‐specific primers of OsPR5 (LOC_Os12g43430; Chanclud et al , 2018), OsPAL3 (LOC_Os02g41670; Chen et al , 2018), OsNPR1 (LOC_Os01g09800; Chern et al , 2005, Yuan et al , 2007), OsPR10 (LOC_Os12g36850; Chanclud et al , 2018), OsPBZ1 (LOC_Os12g36880; Chanclud et al , 2018), OsPOX 8.1 (LOC_Os07g48010; Chittoor et al, 1997), xopQ, xopX and OsGAPDH (LOC_Os04g40950; Jha et al , 2010) as listed in Table S4, using Power SYBR Green PCR Master Mix (Thermo Fisher Scientific) in ViiA 7 Real‐Time PCR System (Applied Biosystems, Foster City, CA, USA). Relative expression was calculated with respect to AGL1‐treated leaves.…”