Developmental and thermal regulation of the maize heat shock protein, HSP101

The plant heat stress protein, Hsp101, and the yeast ortholog, Hsp104, are required to confer thermotolerance in plants and yeast (Saccharomyces cerev isiae), respectively. In addition to its function during stress, Hsp101 is developmentally regulated in plants although its function during developmen t is not known. To determine how the expression of Hsp101 is regulated in c ereals, we investigated the Hsp101 expression profile in developing maize ( Zea mays). Hsp101 protein was most abundant in the developing tassel, ear, silks, endosperm, and embryo. It was less abundant in the vegetative and fl oral meristematic regions and was present at only a low level in the anther s and tassel at anthesis, mature pollen, roots, and leaves. As expected, he at treatment resulted in an increase in the level of Hsp101 protein in seve ral organs. In expanding foliar leaves, husk leaves, the tassel at the prem eiosis stage of development, or pre-anthesis anthers, however, the heat-med iated increase in protein was not accompanied by an equivalent increase in mRNA. In contrast, the level of Hsp101 transcript increased in the tassel a t anthesis following a heat stress without art increase in Hsp101 protein. In other organs such as the vegetative and floral meristematic regions, ful ly expanded foliar leaves, the young ear, and roots, the heat-induced incre ase in Hsp101 protein was accompanied by a corresponding increase in Hsp101 transcript level. However, anthers at anthesis, mature pollen, developing endosperm, and embryos largely failed to mount a heat stress response at th e level of Hsp101 protein or mRNA, indicating that Hsp101 expression is not heat inducible in these organs. In situ RNA localization analysis revealed that Hsp101 mRNA accumulated in the subaleurone and aleurone of developing kernels and was highest in the root cap meristem and quiescent center of h eat-stressed roots. These data suggest an organ-specific control of Hsp101 expression during development and following a heat stress through mechanism s that may include posttranscriptional regulation.