Identification and characterization of a novel stay-green QTL that increases yield in maize.

Jun Zhang,Zhenglin Hou,Stephen P Moose,Hua Mo,Bo Shen,Nick Mongar,Farag Ibraheem,Kankshita Swaminathan,Jennifer Arp,Yang Wang,Angela Bryant,John L Van Hemert,Rajeev Gupta,Kevin A Fengler,William B Allen,Jindong Sun,Renee Lafitte,Bailin Li,Benjamin Weers

doi:10.1111/pbi.13139

Abstract

SummaryFunctional stay‐green is a valuable trait that extends the photosynthetic period, increases source capacity and biomass and ultimately translates to higher grain yield. Selection for higher yields has increased stay‐green in modern maize hybrids. Here, we report a novel QTL controlling functional stay‐green that was discovered in a mapping population derived from the Illinois High Protein 1 (IHP1) and Illinois Low Protein 1 (ILP1) lines, which show very different rates of leaf senescence. This QTL was mapped to a single gene containing a NAC‐domain transcription factor that we named nac7. Transgenic maize lines where nac7 was down‐regulated by RNAi showed delayed senescence and increased both biomass and nitrogen accumulation in vegetative tissues, demonstrating NAC7 functions as a negative regulator of the stay‐green trait. More importantly, crosses between nac7 RNAi parents and two different elite inbred testers produced hybrids with prolonged stay‐green and increased grain yield by an average 0.29 megagram/hectare (4.6 bushel/acre), in 2 years of multi‐environment field trials. Subsequent RNAseq experiments, one employing nac7 RNAi leaves and the other using leaf protoplasts overexpressing Nac7, revealed an important role for NAC7 in regulating genes in photosynthesis, chlorophyll degradation and protein turnover pathways that each contribute to the functional stay‐green phenotype. We further determined the putative target of NAC7 and provided a logical extension for the role of NAC7 in regulating resource allocation from vegetative source to reproductive sink tissues. Collectively, our findings make a compelling case for NAC7 as a target for improving functional stay‐green and yields in maize and other crops.

Highlights

The demand for yield improvement with new technologies is rising because of increasing global demand for food and feed, and the dwindling supply of arable land available for agriculture (Pingali, 2012)
We identified a QTL associated with leaf senescence and nitrogen remobilization from Illinois High Protein 1 (IHP1) 9 Illinois Low Protein 1 (ILP1) crosses
A clear contrast in the rate of leaf senescence was observed between the IHP1 and ILP1 inbred lines in 4-week-old seedlings at the V4 stage (Figure 1a), and these differences were apparent throughout plant development (Figure S1)

Summary

Introduction

The demand for yield improvement with new technologies is rising because of increasing global demand for food and feed, and the dwindling supply of arable land available for agriculture (Pingali, 2012). Crops such as corn, soybean, wheat, rice and canola account for over half of total human caloric intake either through direct consumption or the meat products raised on processed seeds. There are two types of stay-green: cosmetic and functional. Functional stay-green is defined as retaining both greenness and photosynthetic competence significantly longer along senescence (Hortensteiner, 2009). The functional stay-green trait during the final stage of leaf development is important to increase source strength in grain production

Results

Discussion

Conclusion