RICE GERMINATION UNDER SUBMERGENCE

Submergence is one of three natural calamities, together with drought and salinity, which affects crops in term of damage or complete yield loss. Crop species and developmental stage can influence the plant response. Most crops are very sensitive to flooding patterns, especially at germination stage. Therefore, flood events can affect global food security. Current and future climate change scenarios increases the concerns about the impact of excess flooding on crops growing areas. Rice is the only cereal which can germinate and grow well under water submergence and anoxic conditions. The trait of anaerobic germination capacity is characterized by the possibility to use starch under low oxygen and to elongate the coleoptile under water to reach the air surface. This ensures a fast seedlings establishment in paddy fields. Many studies were conducted to clarify the mechanism behind this trait. Recently, trehalose 6 phosphate phosphatase 7 (TPP7) gene availability at chromosome 7 was identified to have a key role in a higher capacity for rice to use starch under germination and thus to growth vigorously when flooded. In our first work, using a panel of japonica rice selected in Italy, we identified the presence of TPP7 gene in the majority of the accessions. A genome-wide association study (GWAS) was conducted on the rice panel in order to find specific chromosomic regions associated to investigated traits. Among the genes polymorphisms identified on 11 significant marker-trait associations (MTA) detected across all the 12 rice chromosomes, we identified a subgroup of genes whose allelic variation could affect the phenotypic response and thus the final coleoptile length under submergence. In a second work, taking advantage from the GWAS results, we investigated the role of auxin in determining the length of rice coleoptile under flooded condition. Our study suggest that, while starch catabolism is necessary for seed germination and coleoptile elongation of japonica rice under submergence, auxin transport plays a role in the development of a long coleoptile under these conditions.