Translating auxin responses into ovules, seeds and yield: insight from Arabidopsis and the cereals

Abstract

Grain production in cereal crops depends upon the stable formation of male and female germ cells in the flower. In most angiosperms, the female germ cells are located deep within the ovary, protected by several layers of maternal tissue, including the ovary wall, ovule integuments and nucellus. In the field, germline formation and floret fertility are major determinants of yield potential, contributing to traits such as seed number, weight and size. Despite this, viable gametes are not the sole determinants of yield. Stimuli affecting the timing and duration of reproductive phases, as well as the viability, size and number of cells within reproductive organs also play a role. One key stimulant is the phytohormone auxin, which influences growth and morphogenesis of female tissues during gynoecium development, gametophyte formation, and endosperm cellularization. In this review we consider the role of the auxin signalling pathway during ovule and seed development, first in the context of Arabidopsis and then in the cereals. We summarise the gene families involved and highlight distinct expression patterns that suggest a range of roles in reproductive cell specification and fate. This is discussed in terms of seed production and how targeted modification of different tissues might facilitate improvements.