A Novel Stay-Green Mutant of Rice with Delayed Leaf Senescence and Better Harvest Index Confers Drought Tolerance.

M K Ramkumar,Ashok Kumar Singh,Trilochan Mohapatra,Nagendra Kumar Singh,Kishor Gaikwad,Viswanathan Chinnusamy,Rakesh Pandey,Amitha Mithra Sevanthi,S Senthil Kumar

doi:10.3390/plants8100375

Abstract

Three Ethyl methansulphonate (EMS)-induced stay-green mutants (SGM-1, SGM-2 and SGM-3) and their wild-type (WT), were tested for their Stay-Green (SG) and drought tolerance nature as the relation between these two attributes is not yet established in rice. In the dark induced senescence assay, SGM-3 showed delayed senescence while SGM-1 and SGM-2 showed complete lack of senescence. Mutants showed stable transcript abundance over time, for 15 candidate genes (CGs) associated with senescence, compared to the WT. SGM-3 however showed moderately increasing transcript abundance over time for ATG6a, ATG4a, NYC1, NOL and NYC3. Only SGM-3 performed better than the WT for yield and harvest index under well irrigated as well as drought conditions, though all the mutants showed better performance for other agronomic traits under both the conditions and ascorbate peroxidase activity under drought. Thus, SG trait showed positive correlation with drought tolerance though only SGM-3 could convert this into higher harvest index. Sequence analysis of 80 senescence-associated genes including the 15 CGs showed non-synonymous mutations in four and six genes in SGM-1 and SGM-2 respectively, while no SNPs were found in SGM-3. Analysis of the earlier reported Quantitative Trait Loci (QTL) regions in SGM-3 revealed negligible variations from WT, suggesting it to be a novel SG mutant.

Highlights

Constant decline in the availability of water resources on one hand and increased utilization of the same resources on the other hand has made drought stress a real threat to global food security [1,2].Plants, being rooted to the ground, have developed tolerance mechanisms to drought stress by altering their morphological, physiological and molecular mechanisms [3,4,5]
On physiological maturity, SGM-1 and SGM-2 panicles remained completely green while SGM-3 turned brown with some tinges of greenness (Figure 1D)
Since SGM-3 behaved like a functional mutant in our study with better performance under drought and showed no variations in the 80 candidate genes tested other than a single non-synonymous mutation in ACC oxidase, which was again common to all the 3 mutants, we looked for mutations within the only known main effect Quantitative Trait Loci (QTL) on chromosome 9 reported from the functional SG mutant, SNU-SG1 [46]

Summary

Introduction

Plants, being rooted to the ground, have developed tolerance mechanisms to drought stress by altering their morphological, physiological and molecular mechanisms [3,4,5]. The magnitude of drought stress experienced by a plant depends on the growth stage of the plant and the duration of the stress. Rice (Oryza sativa L.), a monocot with shallow root architecture but huge water requirement for cultivation—is more prone to water deficit stress than other major food crops [6]. Though rice is vulnerable to drought stress, invariably, across all the growth stages, reproductive stage stress causes more adverse effects as grain yield gets compromised [7]. Drought stress destabilizes the photosynthetic machinery, leading to fluctuations in the carbon and nitrogen metabolism

Methods

Results

Conclusion