Seed yield, a major determinant for the commercial success of grain crops, is dramatically reduced by environmental stresses, such as drought, salinity, and extreme temperatures. Salinity, in particular, is a major problem for crop yield known to affect about 20% of all arable land and cause huge economic losses worldwide. Flowering plants are particularly sensitive to environmental stress during sexual reproduction, and even a short exposure to stressing conditions can severely hamper reproductive success, and reduce crop yield. Since proline is required for pollen fertility and accumulates in plant tissues in response to different abiotic stresses, a role of proline in pollen protection under salt stress conditions can be envisaged. In this project, we aim to specifically raise the levels of proline in Arabidopsis pollen grains, to evaluate the feasibility of this biotechnological strategy to stabilize seed yield under saline conditions.
Despite the large body of information on the effects of drought and heat stress on pollen development, the effects of salt stress on reproductive development have received relatively less attention. Most of the available information focused on and describes the effects of salt stress at the germination stage or on overall plant growth. The reduction of productivity often reported under salinity conditions was usually considered as the final consequence of damage suffered in earlier developmental stages.
However, most of the yield reduction caused by environmental stress can be accounted for by hampered pollen viability and consequently reduced ovule fertilization. In maize, for example, a strict correlation between pollen viability and desiccation tolerance was reported by (Barnabas et al., 2008). The sensitivity of the reproductive phase to drought is even more evident in rice, where water stress was reported to dramatically decrease the harvest index mainly because of a strong reduction in grain set (Ekanayake et al., 1989; Garrity and O'Toole, 1994). The sterility of the rice spikelets was found associated with defects in sexual reproduction, such as incomplete pollen development, incomplete anther dehiscence, and precocious grain abortion soon after fertilization (Namuco and O'Toole, 1986). A positive relationship between grain yield and pollen fertility in wheat under drought or heat conditions also has been described in several reports (Lalonde et al., 1997; Yu et al., 2019).
Undoubtedly, harsh conditions with high salinity have poisonous effects on germination and plant growth and ultimately impair fruit or seed yield. Most glycophytic plants are severely stressed, and stop growing at salt concentrations higher than 200 mM. Much more frequently, however, plants experience moderate or temporary saline conditions caused by sudden bursts of high temperatures, prolonged drought periods or insufficient irrigation regimes. In such conditions, plant growth continues, but development is strongly affected and may severely limit seed set and maturation.
This proposal is specifically designed to tackle moderate or transient peaks of salinity occurring during the reproductive phase. To achieve this goal we will exploit the dual properties of the amino acid proline to protect pollen from salt stress as well as to sustain its development and fertility. This strategy represents a novel biotechnological approach, potentially capable to sustain seed productivity under saline conditions.
References
Barnabas, B., Jager, K., and Feher, A. (2008). Plant Cell Environ 31(1), 11-38.
Ekanayake, I.J., De Datta, S.K., and Steponkus, P.L. (1989). Annals of Botany 63(2), 257-264.
Garrity, D.P., and O'Toole, J.C. (1994). Field Crops Research 39(2), 99-110.
Lalonde, S., Beebe, D.U., and Saini, H.S. (1997). Sexual Plant Reproduction 10(1), 40-48.
Namuco, O.S., and O'Toole, J.C. (1986). Crop Science 26(2), 317-321.
Yu, J., Jiang, M., and Guo, C. (2019). International Journal of Molecular Sciences 20(7), 1550.