Genetic dissection of ovule and embryo abortion in heat-stressed pea

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Pea plants and crops are sensitive to stress like heat and drought, and readily abort flowers and young pods, lowering yields. An ovule is a potential pea seed within a pod before it is fertilized by pollen. On successful pollination, each fertilized ovule contains a small embryo that develops into a seed. Flower and seed loss is likely because ovules are susceptible to heat damage. While pollination is known to be fussy about heat and high temperature days, we know far less about how ovules and young embryos fare in heat. This project looks at pea varieties and develops methods to measure heat stress on ovules hidden inside flowers. We are first using two traditional methods on tiny pods and their ovules, collected from plants four days after a flower is open. Here we can view ovule health with a fluorescent stain under the microscope that highlights wound tissue, called callose, on the ovule surface. We also use a purple stain that allows us to see inside an ovule to the developing embryo in an embryo sac. We plan to measure the amount of callose and size of the embryo and its embryo sac, with and without heat stress. Our project will then enable us to view ovules even earlier in development, and see if the DNA is damaged in cell nuclei. If we see ovules starting to die, we can determine if abortion was caused by heat damage to DNA or if the mother pod was starving the ovules. We also plan to look at gene expression of pollen, tiny pods, their ovules and young embryos, with and without heat stress. We plan to find a way using gene expression from RNA sequencing to identify ovule susceptibility to stress even earlier to the open flower stage. We will use our microscopy methods to measure 18 pea varieties to find the best varieties that can keep ovules alive in a heat wave, so they can be used to develop future pea varieties that can stand up to our warmer summers. Ultimately, our results will identify the best varieties with the most ovule heat-resistance, and even better, add some new experimental methods we can use to simplify and automate for finding better and robust seeds. This research is an industry partnership between the University of Saskatchewan and Saskatchewan Pulse Growers, with collaboration from the federal government.