Closer vein spacing by ectopic expression of nucleotide-binding and leucine-rich repeat proteins in rice leaves

Shuen-Fang Lo,I.-Lun Liu,Samart Wanchana,Anindya Bandyopadhyay,Yue-Ie Hsing,Yu-Pei Chang,Jolly Chatterjee,Pei-Jing Chen,Akshaya K Biswal,Abigail Elmido-Mabilangan,William Paul Quick,Robert A Nepomuceno

doi:10.1007/s00299-021-02810-5

Abstract

Key messageElevated expression of nucleotide-binding and leucine-rich repeat proteins led to closer vein spacing and higher vein density in rice leaves.To feed the growing global population and mitigate the negative effects of climate change, there is a need to improve the photosynthetic capacity and efficiency of major crops such as rice to enhance grain yield potential. Alterations in internal leaf morphology and cellular architecture are needed to underpin some of these improvements. One of the targets is to generate a “Kranz-like” anatomy in leaves that includes decreased interveinal spacing close to that in C4 plant species. As C4 photosynthesis has evolved from C3 photosynthesis independently in multiple lineages, the genes required to facilitate C4 may already be present in the rice genome. The Taiwan Rice Insertional Mutants (TRIM) population offers the advantage of gain-of-function phenotype trapping, which accelerates the identification of rice gene function. In the present study, we screened the TRIM population to determine the extent to which genetic plasticity can alter vein density (VD) in rice. Close vein spacing mutant 1 (CVS1), identified from a VD screening of approximately 17,000 TRIM lines, conferred heritable high leaf VD. Increased vein number in CVS1 was confirmed to be associated with activated expression of two nucleotide-binding and leucine-rich repeat (NB-LRR) proteins. Overexpression of the two NB-LRR genes individually in rice recapitulates the high VD phenotype, due mainly to reduced interveinal mesophyll cell (M cell) number, length, bulliform cell size and thus interveinal distance. Our studies demonstrate that the trait of high VD in rice can be achieved by elevated expression of NB-LRR proteins limited to no yield penalty.

Highlights

Rice is a major staple crop that feeds more of the human population than any other crop
High-throughput screen for leaf vein density (VD), we identified mutant lines with a heritable increase in the number of veins per unit leaf width due to a reduction in the interveinal distance, a phenotype designated as close vein spacing (CVS)
The threshold VD for a mutant to be considered as a Close vein spacing (CVS) candidate was set at 7 veins per mm leaf width, which is above the maximum VD of the WT population

Summary

Introduction

Rice is a major staple crop that feeds more of the human population than any other crop. The rice yield needs to be significantly increased to secure food supplies in the few decades. One important strategy to significantly enhance rice productivity is to introduce C 4 photosynthesis into rice, as C4 crops have higher photosynthetic capacity, reduced water loss, increased nitrogen (N) use efficiency and higher yields, when grown in hot and dry environments (Furbank et al 2009; Hibberd et al 2008). Recent developments in engineering C4 photosynthesis into rice to promote photosynthetic efficiency and yield potential have led to renewed interest in this area (Ermakova et al 2020; Hibberd et al 2008; von Caemmerer et al 2012a, b). The alteration of internal leaf architecture is one of the key prerequisites for establishing the “Kranz anatomy” (Lundgren et al 2014; Sage et al 2014)

Methods

Results

Conclusion