Abstract
In the recent time, Submergence1 (Sub1)QTL, responsible for imparting tolerance to flash flooding, has been introduced in many rice cultivars, but resilience of the QTL to stagnant flooding (SF) is not known. The response of Sub1-introgression has been tested on physiology, molecular biology and yield of two popular rice cultivars (Swarna and Savitri) by comparison of the parental and Sub1-introgression lines (SwarnaSub1 and SavitriSub1) under SF. Compared to control condition SF reduced grain yield and tiller number and increased plant height and Sub1- introgression mostly matched these effects. SF increased ethylene production by over-expression of ACC-synthase and ACC-oxidase enzyme genes of panicle before anthesis in the parental lines. Expression of the genes changed with Sub1-introgression, where some enzyme isoform genes over-expressed after anthesis under SF. Activities of endosperm starch synthesizing enzymes SUS and AGPase declined concomitantly with rise ethylene production in the Sub1-introgressed lines resulting in low starch synthesis and accumulation of soluble carbohydrates in the developing spikelets. In conclusion, Sub1-introgression into the cultivars increased susceptibility to SF. Subjected to SF, the QTL promoted genesis of ethylene in the panicle at anthesis to the detriment of grain yield, while compromising with morphological features like tiller production and stem elongation.
Highlights
The uncertainty of occurrence, duration, and amount of rainfall affect productivity of the rainfed lowland and flood-prone rice ecosystem[1,2,3]
Deep water rice survives drowning through matchable growth response by promoting internode elongation and keeps afloat the upper leaves above water level for normal gas exchange
Hattori et al.[28] reported that two ERF DNA binding proteins SNORKEL1 and SNORKEL2 allow the plant to adapt to deep water, where ethylene generated in plant organs under submergence down-regulates ABA response, thereby permitting GA action for stem elongation[27]
Summary
The uncertainty of occurrence, duration, and amount of rainfall affect productivity of the rainfed lowland and flood-prone rice ecosystem[1,2,3]. Sub1A gene encoding ERF transcription factor confers tolerance to flooding in rice[8]. It reduces ethylene sensitivity of rice plants under submergence and thereby checks rapid stem elongation and chlorophyll degradation[9,10]. Based on a simple logic that expression of Sub[1] QTL encoding ERF in the Sub1-introgressed rice cultivars under SF can underscore the expression of ethylene response genes and thereby ameliorate adverse effects on grain-filling, an experiment has been designed to evaluate two popular rice cultivars and their Sub1-introgressed near isogenic lines to different levels of SF in simulated conditions
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