Memory over the Generations: Chilling Tolerance at Booting Stage of Next Generation Can be Improved By Abiotic Stresses in Rice.

Stress tolerances of crops are basically controlled genetically, but they can also be affected epigenetically.  Here, we verified a hypothesis that chilling tolerance at the booting stage of rice (Oryza sativaL.) for inducing spikelet sterility in the next generation can be improved by environmental cues in the previous generation.  In the previous generation in 2012, we grew rice plants of two cultivars, Sasanishiki and Hitomebore, on 4L pots in water temperature controlled tubs at 21.5C throughout the season, and exposed the plants to either shading treatment (90%) or salt treatment (EC 9.0mS/s) at either of two periods during vegetative growth (I: 2nd -20th of June, II: 21th June-10th July) at open fields of Iwate University.  During the reproductive growth period, the plants were examined the levels of  chilling tolerance and gene expression of spikelets, and some of the plants were grown under optimal conditions for the next generation experiments. In the next generation in 2013, we investigated the impact of low temperature during reproductive stage inducing spikelet sterility in two experimental fields in Iwate Biotechnology Research Center (IBRC, Iwate Pref., Japan) and National Agric. Res. Center (NARO, Akita Pref., Japan). Total number of spikelets per panicle and the percentage of spikelets sterility were measured.  In the previous generation, both shading and salt treatments significantly increased spikelet sterility induced by low temperature during reproductive growth by about 10 ~ 30% than control for both cultivars and both treatment periods (I or II).  In the next generation, the spikelet sterility by low temperature was significantly reduced by the previous-year’s shade and salt treatments for both cultivars and both treatment periods than control, which was observed at both experimental locations.  We firstly revealed the evidence of epigenetic control of chilling tolerance of rice, and we will discuss about the regulation of genes related to this phenomenon.