Plant nuclear factor Y (NF-Y) B subunits confer drought tolerance and lead to improved corn yields on water-limited acres

Abstract

Commercially improved crop performance under drought conditions has been challenging because of the complexity of the trait and the multitude of factors that influence yield. Here we report the results of a functional genomics approach that identified a transcription factor from the nuclear factor Y (NF-Y) family, AtNF-YB1, which acts through a previously undescribed mechanism to confer improved performance in Arabidopsis under drought conditions. An orthologous maize transcription factor, ZmNF-YB2, is shown to have an equivalent activity. Under water-limited conditions, transgenic maize plants with increased ZmNF-YB2 expression show tolerance to drought based on the responses of a number of stress-related parameters, including chlorophyll content, stomatal conductance, leaf temperature, reduced wilting, and maintenance of photosynthesis. These stress adaptations contribute to a grain yield advantage to maize under water-limited environments. The application of this technology has the potential to significantly impact maize production systems that experience drought.

Fig. 1.

Constitutive expression of AtNF-YB1 confers drought tolerance in Arabidopsis. Representative pots of transgenic plants (Left) and controls (Right) are shown at the end of a dry-down period (Upper) and at 5 days after rewatering (Lower).

Fig. 2.

Arabidopsis transgenic lines have improved drought physiology. Water potential (Upper) and photosynthesis measured under saturating CO₂ conditions (Lower) of Arabidopsis plants measured during a stress treatment applied at the early reproductive stage of development.

Fig. 3.

Agglomerative cluster of all genes (minus hybridization controls) that are differentially expressed in the seedling profiles from 35S::CBF4 plants or 35S::AtNF-YB1 (vs. wild-type) plants, as well as the regulation of those genes at 4 h after treatment with ABA in wild type (vs. mock-treated wild-type plants). Red indicates induction, and green indicates repression. White bars indicate that the gene did not display a significant change in expression (P < 0.01). An ordered list of the genes included in the heatmap and the corresponding expression data can be found in SI Table 3.

Fig. 4.

Quantitative RT-PCR was used to measure AtNF-YB1 transcript accumulation in wild-type plants over a drought timecourse. Relative water contents for the indicated treatments were 0.82 (well watered), 0.81 (mild drought), 0.60 (moderate drought), 0.29 (severe drought), 0.65 (2 h rewater), and 0.81 (23 h rewater). The y axis indicates the 18S RNA-normalized PCR cycle threshold for transcript detection. At severe drought treatment, AtNF-YB1 crosses the detection threshold ≈3.5 cycles before the transcript in well watered conditions, indicating an ≈12-fold increase in expression during severe drought. Error bars indicate the standard deviation measured in two biological replicates. Numbers at the base of each bar indicate the P value resulting from a heteroscedastic two-tailed t test between the well watered and each drought treatment.

Fig. 5.

Transgenic maize plants in greenhouse and field have visually observable improved drought tolerance. In both photographs, controls are in the left flat or row, and transgenics expressing ZmNF-YB2 are in the right flat or row.

Fig. 6.

Three transgenic maize lines demonstrate improved yield in 2 years of yield testing. Values plotted are increase on a percentage basis of transgenics over controls. All differences plotted are significant at P < 0.1. Data from three independent lines are shown with side-by-side comparison of 2 years' results. Base yield (yield of controls) was 4.6 metric tons/hectare (74 bushels/acre) in Year 1 and 6.4 metric tons/hectare (102 bushels/acre) in Year 2.