OsTSD2‐mediated cell wall modification affects ion homeostasis and salt tolerance

Salt stress is a major environmental threat to meeting the food demands of an increasing global population. The identification and exploitation of salt adaption mechanisms in plants are therefore vital for crop breeding. We here define the rice mutant (sstm1) whose salt sensitivity was unambiguously assigned to a single T‐DNA insertion through segregational analysis following backcrossing to the wild type line. Insertion was within OsTSD2, which encoded a pectin methyltransferase. The sstm1 and allelic mutants, collectively known as tsd2, displayed higher content of Na+ and lower level of K+ in the shoot, which is likely to lead to reduced salt tolerance. Molecular analysis revealed reduced expression of the genes maintaining K+/Na+ homeostasis in tsd2, including OsHKT1;5, OsSOS1, and OsKAT1. Furthermore, OsTSD2 influenced ion distribution between the hull and the rice seed, which could improve food safety with heavy metal pollution. Amino acid levels tended to be increased in tsd2 mutants, implicating a role of pectin in the regulation of metabolism. Taken together, we have demonstrated an important facet of salt tolerance, which implicated OsTSD2‐mediated cell wall pectin modification as a key component that could be widely applied in crop science. To uncover novel genetic determinants for rice salt tolerance, we performed a genetic screen and identified a salt‐sensitive mutant, carrying a mutation in OsTSD2, which encodes a pectin methyltransferase. Mutation of OsTSD2 led to the high content of Na+ and reduced accumulation of K+ the shoot. We identified the role pectin modification played in ion homeostasis and salt tolerance, notwithstanding that the essential mechanism remains to be explored. Moreover, wider potential applications for quality improvement in rice are suggested due to the influence of OsTSD2 on metabolism, the ion content of seeds, and distribution between the hull and seed.